term one Flashcards
1
Q
state the three elements of cell theory
A
- all living organisms are made up of one or more cells
- the cell is the basic unit of life
- cells arise from existing cells by division
2
Q
true or false
- all cells are surrounded by a plasma membrane
- all cells are surrounded by a cell wall
- all cells contain genetic material in the form of DNA
- all cells contain DNA in a nucleus
- all cells perform metabolism
- all cells can move
A
true
false
true and false (exception is red blood cells)
false
true
all cells can move
3
Q
in EUKARYOTIC cells, DNA is contained in
A
the nucleus
4
Q
prokaryotic vs eukaryotic cells
A
PRO:
- no nucleus
- always single cellular
includes both
a) bacteria (formally eubacteria), including cyanobacteria (photosynthetic, formally known as blue-green algae)
b) archaea: many species live in extreme environments (halophiles = high salt, thermoacidophiles)
EUK:
- contain a nucleus
- single or multi cellular
includes
1. plants - multi
2. animals - multi
3. fungi (both single and multicellular - yeast and mould are single)
4. protozoans (single cellular)
5
Q
cell plasma membrane
A
- bilayer of phospholipids, cholesterol and embedded transmembrane proteins
phospholipids = amphipathic = hydrophilic phosphate group and hydrophobic lipid tails - dynamic lipid rafts: specialised platforms were specific transmembrane proteins are concentrated
4 main roles
1. barrier
2. communication
3. import and export
4. electrical capacitor
6
Q
cytoskeleton
A
system of filaments that are present in the cytoplasm of eukaryotic cells
3 main filaments make up a network of protein fibres
1. actin filaments
2. intermediate filaments
3. microtubules
main roles
1. maintenance of shape, stability
2. adaption of shape
3. cell division
4. motility
5. movement of particles within cells
7
Q
cytoplasm (cytosol)
A
- aqueous solution of defined pH of 7.2 and ion composition
also contains
1. a high concentration of proteins (metabolic enzymes, intracellular messengers)
2. tRNAs
3. free ribosomes
4. inclusion bodies (eg glycogen granules)
5. mitochondrial DNA
8
Q
the nucleus
A
- surrounded by two layers of membrane (two lipid double layers) which form the nuclear envelope
- contains nucleoplasm
- contains chromosomal DNA + packaging proteins (histones) and gene regulatory proteins
- site of RNA synthesis and processing (RNA splicing)
- nucleolus: site of ribosome synthesis (and signal recognition particle), can capture gene regulatory proteins (nucleolar detention)
9
Q
endoplasmic reticulum
A
- network of interconnected membrane vesicles (cisternae), continuous with the outer nuclear membrane
- rough er: synthesis of secreted and transmembrane proteins, contains ribosomes
smooth er: synthesis of lipids and steroid hormones, detoxification (liver), release of glucose from the liver
10
Q
mitochondria
A
- often oval or sausage shaped
- 1.5-1 x 1-2 micro metres
- double membrane: inner membrane folded into cristae (high transmembrane protein content)
- contains circular DNA (mtDNA) and ribosomes in matrix
- own genetic code
functions
1. respiration/ oxidative phosphorylation (electron transport chain)
2. citric acid (krebs) cycle
3. heat production
4. Ca2+ storage
5. programmed cell death (apoptosis)
mitochondrial disorders: mutations in mtDNA (eg Kearns-Sayre syndrome) defects in nuclear genes that encode mitochondrial proteins (hereditary spastic paralegia)
11
Q
golgi apparatus
A
- stack of flattened membrane vesicles
- modification of proteins destined for secretion and transmembrane proteins
pathway of a secreted protein: rER - cis golgi - trans golgi - secretory vesicles
12
Q
lysosomes
A
- membrane bound organelles found in animal cells
- degrade unwanted proteins and particles taken up by the cell, and membranes and organelles that are no longer needed
- acidic pH = 4.5-5 is the optimal environment for degradative enzymes
- degradation of pathogens by macrophages
13
Q
peroxisomes
A
- degrade fatty acids and toxic compounds
- fatty acid oxidation produces precursors for biosynthetic pathways
- oxidation produces H202 (corrosive)
the enzyme catalase neutralises H202:
2H202 = 2H20 + O2
detoxification of ethanol in the liver
C2H5OH + H2020 = CH3CHO + 2H20
14
Q
conditions on earth before life forms existed
A
- lots of methane
- increased amounts of co2
- little/ no oxygen
- higher temps
- lots of lightning and volcanic eruptions (energy)
- no UV protection from atmosphere (no ozone)
- these conditions promoted spontaneous reaction
- promoted the formation of carbon compounds
- living organisms then changed these spontaneous conditions
15
Q
where did the first cell come from
what did the first cell contain
A
- ideal reaction conditions (high temp and pressure)
- catalysts (metals) lead to the self-assembly of polymers and self replicating molecules (RNA)
- compartmentalisation: phospholipids formed partially permeable membranes
- rna
- membrane enclosed rna
- lipid membrane
16
Q
what was the first genetic material
A
RNA
- can store genetic information
- is self-replicating
- can act as an enzyme
- mutates at a higher rate and is more prone to mutations
17
Q
evolution of LUCA (the last universal common ancestor of cells)
A
- simple molecules such as HCHO, HCN, cyanamide etc providing all the right conditions
- minerals acted as catalysts, in high temperature environments in hydrothermal vents
- then we have the RNA world
- over time, DNA became the more stable genetic material
- membrane formation: lipid bilayers spontaneously formed vesicles, providing a compartment for early cellular processes
18
Q
bacteria and archaea
A
- one cellular compartment, no membrane bound organelles
- specialisations eg flagella
- huge variety - 1 billion species
- achaea can adapt to extreme environments and sources of energy
- reproduction: error prone but fast
19
Q
The Endosymbiotic Theory:
A
scientific explanation for the origin of certain organelles in eukaryotic cells, particularly mitochondria and chloroplasts.
20
Q
how did mitochondria and chloroplasts evolve?
A
mitochondria:
1. There was an early eukaryotic cell that didn’t use oxygen to make energy
2. This cell engulfed a smaller bacterium that did use oxygen. The bacterium provided the cell with extra energy.
3. The bacterium and cell started living together in a symbiotic relationship
4. Over time, the bacterium evolved into the mitochondrion.
chloroplast:
1. The cyanobacterium turned into chloroplasts
Photosynthesis happens in 2 steps: photosystem I and II.
- Photosystem I is similar to what we find in green sulfur bacteria and heliobacteria
- Photosystem II is similar to the system found in purple bacteria and green filamentous bacteria.
- These bacteria contributed their ability to do photosynthesis when they became part of the eukaryotic cell, eventually helping the chloroplasts do photosynthesis efficiently.
21
Q
protozoans
A
- single celled eukaryotes
- motility, predation
- not animals, plants or fungi
22
Q
ex ovo omnia
asexual reproduction
sexual reproduction
A
everything from the egg
- yeast and hydra
- can include parthenogenesis - eggs can give rise to an organism without undergoing fertilisation - only contains maternal genetic information
- Embryogenesis: process of forming a new organism from a fertilised egg. Requires precise control over cell division, tissue formation (morphogenesis), and cell specialization (differentiation) to create a properly functioning organism.
- formation of an organism involves cell proliferation, differentiation and morphogenesis
23
Q
origins of multicellularity
A
volvox: example to explore multicellularity
- In volvox, there are two types of cells with specialised roles: somatic and germ cells
Somatic: differentiated, non-reproductive cells. They are mortal
Germ: reproductive cells that give rise to new individuals. They are immortal as they can regenerate.
24
Q
origins of social behaviour
A
- dictyostelium discoideum: mold, social amoeba
display characteristics of multicellular organisms:
- motility and chemotaxis
- cell adhesion
- phagocytosis
- pattern formation
- cell death
25
pathogens
- disease causing microorganisms or infectious agents
- examples include bacteria, viruses, fungi, and protozoans
26
viruses
virion: the form of a virus outside of a host cell
- contains DNA or RNA, protein coat + sometimes a lipid envelope
- retroviruses and lentiviruses: convert RNA into DNA. DNA integrates into host's genome causing mutagenic events
- lentiviruses: dormant, eg herpes
- usually very small and only visible in EM
- origins
Origins of viruses:
1. Virus first hypothesis: suggests that viruses originated before cells, as self-replicating molecules
2. Cellular origin hypothesis: proposed that viruses originated from cellular genetic material that became parasitic over time
27
which organisms are always unicellular
protozoans
bacteria
yeast
28
three classes of cytoskeleton
actin filaments:
- polymer of actin monomers, 7nm in diameter
- globular protein arranged in a helix
- major contractile component of muscle cells
- found in all eukaryotic cells
Intermediate filaments:
- 8-12nm in diameter
- structural protein in eukaryotic cells
microtubules
- filament of tubulin monomers
- 23nm in diameter
- play a role in cell structure, organisation, mitosis and movement
29
how is actin organised
what are the roles of actin
- organised in bundles or meshed networks/ branched arrays
- defines the shape of cells and cellular sub-structures
- exerts force
- cell movement
- cell division
30
actin based structures in motile cells: these structures are critical in cell motility
1 stress fibres: contractile actin-myosin bundles in the cytoplasm
2. lamellipodium: thin, sheet like extension that contains a dense network of actin filaments
3. filopodia: transient, finger like protrusions that contain loose bundles of actin filaments
31
the actin molecule
- most abundant protein in eukaryotic cells
- 375 amino acids
- 55kDa monomer (G-actin)
- two similar domains
- binds ATP/ADP
- mutations cause multiple disorders including muscular dystrophy and haemolytic anaemias
32
dynamic polymerisation of actin filaments
- G-actin monomers reversibly polymerises G-actin into F-actin filaments, forming a double helical structure
- diameter = 5-8nm
- plus and minus end (barbed and pointed end)
- addition of subunits happens faster at the barbed end
- therefore, actin monomers seem to migrate from the barbed end to the pointed end - this is actin treadmilling
- ATP is hydrolysed to ADP
- approx 60 actin binding proteins regulate this process eg preventing polymerisation or stopping polymerisation
33
how does actin relate to cell division and muscle fibres
Cell division: actin filaments generate contractile forces that divide the cell into 2 daughter cells.
Muscle fibres: in muscle contraction, actin filaments interact with myosin to generate force during contraction.
Actin-myosin = actomyosin (filaments in muscle fibres)
34
sarcomere
- the basic unit of muscle contraction
- composed of both actin and myosin
35
role of actomyosin and myosin II in muscle contraction
The dark bands (A-bands) contain thick filaments (myosin).
The light bands (I-bands) contain thin filaments (actin).
The Z-discs mark the
boundaries of the sarcomere, the functional unit of muscle contraction.
The M-line is in the center, anchoring the thick filaments.
Myosin heads attach to actin, forming actomyosin cross-bridges. Using ATP, myosin pulls actin filaments toward the center, shortening the sarcomere (contraction). This cycle repeats for continued contraction.
myosin II is a motor protein that interacts with f-actin
- Myosin heads bind to actin filaments, pulling them toward the center of the sarcomere.
36
intermediate filaments
- what do they do
- where are they
- provide stability and cohesions against stretch
- stretching a sheet of cells with intermediate filaments keeps cells remaining intact and together
- in the cytoplasm and the nucleus
- cytoplasm:
1. in epithelia: keratins
2, in connective tissue, muscle cells and glial cells: vimentin and vimentin-related
3. in nerve cells: neurofilaments
- nucleus
1. in all animal cells: nuclear lamins
37
keratin monomers as intermediate filaments
- keratin monomers are fibrous filaments
- Primary structure = long chain of amino acids arranged in a specific sequence.
- Secondary structure = forms an alpha helix for strength
- Tertiary and quaternary structure = helices intertwine to form coiled-coils, which assemble into larger filament structures
- mutations in keratin can cause epidermolysis bullosa (EB)
38
nuclear lamins
an intermediate filament protein that forms a mesh-like network called the nuclear lamina.
maintains the shape of the nucleus
This lines the inner side of the nuclear envelope in eukaryotic cells and provides structural support and various regulatory functions
39
microtubules
- cylindrical, hollow structure made of protein subunits called tubulin. Major component of the cytoskeleton
- main component of the mitotic spindle
- Composed of dimers of a- and b- tubulin which polymerise end-to-end to form 13 parallel protofilaments.
- Polarity: b-tubulin has the plus end where rapid growth occurs
- Microtubules originate in MTOCs (microtubule organising centres) such as the centrosome. The centrosome is an MTOC- it becomes duplicated during mitosis.
- Microtubules are the substrate of organelle transport and the major component of cellular cilia
- microtubule-associated proteins regulate microtubule stability
40
motor proteins
- proteins that help to move the cargo along the microtubule network
- can also speed up axonal transport in neurons
- kinesins: carry cargo from the minus end to the plus end
- dynein: from plus to minus end
- utilise ATP to generate kinetic energy
- cargo: proteins, RNA's, vesicles, organelles etc
41
dynein and cilia
- a form of dynein enables cilia to beat
1. beating cilia on epithelia eg for the removal of mucus
2. cilia as signalling antennae
3. cilia in sperm motility
- all these roles can be affected by ciliary mutations including those in ciliary dyneins = Bardet-Biedi Syndrome
42
what are the motor proteins that interact with actin
1. myosin I: transport a vesicle or organelle
2. myosin II: generates a contractile force
43
centrosome definition
the cell's organising centre for microtubule growth
44
what factors destabilise microtubules
Nocodazole,
Colchicine,
Vinblastine
45
what are the two types of extracellular matrix and where are they found
1. basal lamina/ basement membrane
- 2D sheet on which epithelial cells reside
- epithelium
- in the epithelium, cells are tightly packed binding to each other
2. fibrillar matrix
- mesencyhme
- cells are sparse
- 3D matrix composed of various fibres, in which cells such as fibroblasts are buried
46
basal lamia
- underlies epithelia and surrounds some non-epithelial cells such as muscle and the kidney glomerulus
- main components are:
collagen IV, laminin, nidogen, and perlecan
47
fibrillar matrix
- deposited and constantly re-modelled by embedded cells
- main components are:
collagen I
fibronectin
elastin
proteoglycans
48
4 main types of junctional complexes
occluding junctions: eg tight junctions
cell-cell anchoring junctions: eg adherens junctions and desmosomes
cell-matrix anchoring junctions eg focal adhesion and hemidesmosomes
channel forming junctions:
eg gap junctions
49
desmosomes vs hemidesmosomes
desmosomes: pairs of dark, disk structures at cell-cell contacts
- 500nm high
hemidesmosomes: at cell-ECM interface
- 100nm wide
- both are linked to intermediate filaments and help with stability of cells
50
tight junctions
- surround the apical surface of epithelial cells
- cell to cell junction
- tight junction proteins include: claudin and occludin which maintain the barrier function
51
gap junctions
- form pores that allow small molecules and ions to pass between cells
- cell to cell junctions
- Couple cells via permeable pores which allow small molecules and ions to pass between cells = chemical and electrical coupling
52
adherens junctions
- linked to the actin cytoskeleton
- cell to cell junctions
53
focal adhesions
- half an adherens junction
- link the actin cytoskeleton to the ECM via integrins
- form transiently during cell movement
54
cadherins
- ca2+ dependent adhesion molecules that mediate cell-cell adhesion in tissues.
E-cadherin: many epithelia
N-cadherin: neurons, heart, skeletal, muscle, lens and fribroblasts
P-cadherin: placenta, epidermins, breast epithelium
VE-cadherin: endothelial cells
55
which junctions are not based on homophilic interactions
hemidesmosomes
focal adhesions
56
the nervous system
- the main controlling and communicating centre of the body
- coordinates and controls all essential bodily functions
- processes information from the environment and enables the body to respond accordingly
- provides us with higher functions such a memory, emotions and learning
57
are neurons transcriptionally and translationally active
yes
however, they are also postmitotic - chromatin remains in a diffused state
once specialised, they do not divide
58
axonal transport
neuronal components are transported via motor proteins along axonal microtubules
- kinesins:
100-400mm a day
mitochondria and vesicles are transported
- dyneins
50-250mm a day
tranport aging mitochondria and endocytic vesicles
59
what are axons myelinated by
- specialised glial cells
de-myelination in MS
- autoimmune disease of uknown aetiology
60
why is myelination important
-it speeds up nerve conduction: saltatory conduction
61
coverings of peripheral nerves
endoneurium:
delicate connective tissue layer surrounding axon and associates Schwann cells
perineurium:
connective tissue layer surrounding groups of axons forming fasicles
epineurium:
robust connective tissue layer surrounding individual fasicles, contains blood vessels and forms the nerve itself
62
chromatolysis
dissolution of Nissl substance in response to ischemia, axotomy, cell toxicity, infections etc
63
functional classification of neurons
sensory/afferent neurons: send signals towards the CNS
motor/efferent neurons: send signals away from the CNS, into the periphery
interneurons: act locally, within the CNS, and connect neurons with each other
64
structural classification of neurons
multipolar: most neurons in the CNS(eg motor neurons)
bipolar: eg sensory neurons in the retina
(pseudo)unipolar: neurons with a single process that often splits into a peripheral and central branch (eg sensory neurons)
65
3 types of synapse
axo-dendritic
axo-somatic
axo-axonic
66
Convergence vs divergence
Convergence: multiple neurons converge onto a single neuron, allowing integration of multiple inputs from one output
Divergence: a single neuron branches to effect multiple neurones, allowing one signal to have multiple outputs
67
PNS Neuroglia
CNS Neuroglia
- satellite cells and schwann cells
- ependymal cells, oligodendrocytes, astroyctes and microglia
68
fibrous vs protoplasmic astrocytes
fibrous: white matter, support axons, longer processes
protoplasmic: grey matter, homeostatic and other roles. short and dense processes
69
roles of astrocytes
Structural support
Extracellular electrolyte homeostasis (ions, water, pH)
Energy storage (glycogen, glucose, lactate)
Effects of endothelial cells and angiogenic factors = blood-brain-barrier regulation
Glia limitans
Uptake and regulation of neurotransmitters
Glutamate regulation (glutamate/glutamine transport)
Neurotrophic factors neuronal survival, myelination
Neurogenesis and synaptogenesis through modification of the ECM
Inhibition of axon regeneration
Immune modulation (with microglia)
70
astrocytes and buffering K+ ions
astrocytes have important roles in buffering K+ ions, they can siphon them, thereby preventing K+ ion build up and toxicity
71
oligodendrocytes
- a single oligodendrocyte can myelinate multiple different axons
- they inhibit axon regeneration in the CNS
72
microglia
- immune defence and removal of cellular debris in the brain
- pro-inflammatory
- once activated, they retract their processes and become phagocytotic
73
ependymal cells
- found in the lining of the ventricular system and spinal canal
- secrete, monitor and aid in the circulation of CSF
ependymocytes: cilia and microvilli
chloroid plexus: specialised cuboidal epithelium in all ventricles; secretes CSF
74
PNS glia
Schwann cells:
- myelination of PNS axons
- rapid removal of myelin debris by phagocytosis
- promote axon regeneration by producing permissive ECM components and neutrophins
satellite cells:
- structural and metabolic support
75
how are electrode potential measured
1. extracellular recording (electrode outside cell)
2. intracellular recording (electrode inside cell)
3. patch clamping (electron sealed to cell surface)
76
at rest the inside of the membrane is...
when cells become activated...
more negatively charged than the outside (hyperpolarised)
the inside of the membrane becomes more positively charged (depolarised)
77
the electrochemical gradient across a membrane is established because...
1. specialised pumps move ions against their concentration gradients
2. the membrane is relatively permeable, so the movement of ions is restricted to specialised channels in the membrane
3. the membrane acts to separate and store ionic charge differentials between the outside and inside of the cell
78
Na+/K+ ATPase pump
the pump uses energy (ATP) to actively pump three sodium and two potassium ions out and into the cell, respectively, maintaining a more depolarised internal environment
79
the resting membrane potential
-70mV
determined by Na+ and K+ ions
the equilibrium position of an ion is the membrane voltage required to prevent the movement of an ion down its concentration gradient
if the inside of the cell is very negative, K+ will be prevented from leaving
if the inside of the cell is very positive, Na will be prevented from entering
80
how do you calculate membrane voltage potential due to a specific ion
the Nernst equation
81
sodium and potassium channels
- sodium channels permit the rapid influx of sodium into the cell upon opening, with resultant depolarisation (more positive)
- potassium channels permit the rapid efflux of potassium out of the cell upon opening, with resultant hyperpolarisation (more negative)
- the specific ionic distribution across the membrane sets the resting membrane potential
- ions are under two specific forces, the electrostatic force and the force of diffusion
82
action potential: basic principles
1. resting membrane potential
2. depolarising stimuli
3. depolarisation reaches threshold: voltage gates sodium channels open and sodium ions enter neuron
4. rapid Na+ entry depolarises neuron further
5.potassium ions move out of the neuron
6. potassium channels remain open and more K+ leaves the neuron, hyperpolarising it
7. Kv channels close, some K+ enters cell through leak channels
83
functional states of ion channels
1. closed (resting)
2. open (active)
3. inactive (refractory)
- v gated Na channels have all 3
- v gates K channels have no inactivation state
84
two refractory periods
absolute: results from the inactivation of Na+ channels, and lasts until the resting membrane potential is restored
relative: results from the hyperpolarisation phase, during which a greater stimuli is needed to reach threshold
- The membrane potential of the axon is more negative than -70 mV
- results from the delayed closing of potassium channels
85
myelination in the PNS vs the CNS
PNS: schwann cells
CNS: oligodendrocytes
86
Why is the resting potential of a neuronal membrane much closer to the equilibrium potential of K+ than to that of Na+?
The membrane is more permeable for K+ ions at rest because it has a larger number of K+ channels.
87
what would be the membrane potential for a positively charged ion if the concentration outside and inside of the cell are identical?
0mv
88
what is optogenetics
Experimental manipulation of membrane potentials using light-triggered ion channels
89
What establishes the resting potential of a neuron?
The energy-dependent activity of the Na+/K+-ATPase
90
which organelles within a cell have internal membranes
lysosome
mitochondrion
peroxisome
golgi apparatus
endoplasmic reticulum
vesicle
nuclear envelope
91
biological membranes are selectively permeable barrier
- block the passage of almost all water soluble molecules (in and out of cells and organelles)
eg glucose, sucrose
- ions cannot cross
- charged polar molecules cannot cross eg amino acids and ATP
- small uncharged or hydrophobic (lipid soluble) molecules can freely traverse the bilayer by simple diffusion down their concentration gradients eg o2, n2, benzene, short chain fatty acids
- charged polar molecules require specialist proteins to carry them across the membrane eg H20, C02, urea, glycerol
92
TRANSPORT MECHANISMS
do these transport mechanisms
a) need a carrier protein
b) go with or against the concentration gradient
c) require energy
d) give an example
simple diffusion
facilitated diffusion
primary active transport
secondary active transport
no
with
no
H20
yes
with
no
glucose (GLUT)
yes
against
yes (ATP hydrolysis)
Na+/K+- ATPase
yes
against
yes, electrochemical gradient
Na+/glucose transporter in the intestine
93
rate of diffusion depends on..
the octanol/water partition coefficient (Kw) of the solute
94
Kow =
the equilibrium constant for partitioning of a molecule between oil (octanol) and water
- the higher the value for Kow, the more lipid soluble it is
95
different types of gating on ion channels
voltage gated
ligand gates (extracellular ligand)
voltage gated (intracellular ligand)
mechanically gated
96
transport of one solute vs coupled transport
one solute = uniport
coupled transport = symport and and antiport
97
J max =
Km =
maximum rate at which a transporter protein can move a substance across the membrane
affinity constant
higher Km = a lower affinity
98
facilitated glucose transporters
- facilitated glucose transport is medicated by a family of 12 distinct transporters (GLUT1-12)
GLUT 1:
- location: ubiquitous; highly expressed in the BBB and erythrocytes
-Km = 1-2mM
- basal glucose uptake
GLUT 2:
- location: liver, kidney, intestinal epitherlium, pancreatic B cells
-Km: 15-20mM
- glucose sensing and transport when blood glucose is high
GLUT 3:
- locations: neurons
- Km: 1-2mM
- basal glucose uptake
GLUT 4:
- location: muscle
- Km: 5mM
- regulated by insulin
99
regulation of GLUT4 by insulin
1. insulin binds to membrane receptor
2. signals to intracellular pool of GLUT4
3. translocation of GLUT4 to membrane
4. when insulin levels fall GLUT4 recycled back to intracellular pool
100
primary active transport
- energy supplied by the hydrolysis of ATP
- ATP = ADP + Pi
- for example in Na+/K+-ATPase in plasma membrane, the H+-ATPase in lysosomal membrane and the Ca2+-ATPase in plasma membrane; endoplasmic/sarcoplasmic reticulum
101
functioning of the Na+/K+-ATPase
1. Na+ binds to intracellular site
2. this triggers an autophosphorylation of the pump
3. phosphorylation causes a conformational change to release Na+ to the exterior and to expose a K+ binding site
4. binding of K+ triggers dephosphorylation of the pump
5. pump returns to original confirmation and K+ is discharged into the interior of the cell
this is an electrogenic process
102
the NA+/K+-ATPase is a drug target for treatment of congestive heart failure
- in the heart muscle, the Na+/Ca2+ antiporter contributes to the removal of Ca2+ from cytosol allowing cardiac relaxation to occur
- source of digitoxin and digoxin = foxglove
1. oubain inhibits the Na+/K+-ATPase by preventing K+ binding, decreasing the rate of Na+ extrusion from cardiac muscle cells
2. this increases the intracellular Na+, which reduces the activity of NCX, resulting in slower Ca2+ efflux and therefore prolonged high cytostolic Ca2+ to maintain cardiac muscle contraction
103
secondary active transport example
- SGLT1 and SGLT2 are sodium glucose symporters
- utilisation of an electrochemical gradient
important in
1. SGLT1: intestinal epithelial cells for the adsorption of dietary glucose
2. SGLT2: epithelial cells in proximal tubules of the kidney for readsorption of glucose from the primary urine
104
cholera toxin causing electrolyte and fluid losses in the intestine
1. Cholera toxin (CT) binds to the GM1 ganglioside receptor on the apical membrane of intestinal cells
2. CT is internalised by endocytosis and transported through the Golgi to the ER
3. In the ER subunits of the toxin are split and the A1 subunit escapes to the cytosol.
4. A1 binds to and overactivates the heterotrimeric GTPase Gsα, leading to an activation of Adenylyl Cyclase and an increase in cAMP levels
5. This activates the CFTR Cl- channel leading to large Cl- secretion
6. Na+ follows the electrical gradient
7. H2O follows the osmotic gradient
105
role of the Na+/glucose cotransporter in electrolyte replacement therapy in cholera
replacement therapy includes a high concentration of glucose which drives Na+ back into the intestine through the Na+/glucose symporter SGLT1
106
types of synapses
axodendritic
axosomatics
axoaxonic
107
synaptic communication
1. resting synapse
2. AP arrives, V-gated Ca2+ channels open
2. Ca2+ entry triggers exocytosis of synaptic vesicle content
3. NT diffuses across the synaptic cleft and activates postsynaptic cell
108
EPSP
IPSP
excitatory postsynaptic potential
- add to generate depolarisation (more likely to fire an action potential)
inhibitory postsynaptic potential
- add to generate hyperpolarisation (less likely to fire an action potential)
EPSP's and IPSP's act to cancel each other out
109
receptor types
ionotropic:
- ligand activated ion channels
- fast acting, opens and closes quickly
- generates post-synaptic potential
EPSP : Na+, IPSP: K+,Cl-
metabotropic:
- combined to a g protein
- slower acting
- generates a longer lasting more varied response
110
explain the knee jerk reaction
Reflex hammer hits patellar tendon
Stretch receptors in the quadricepts femoris muscle are activated
An action potential travels along an afferent sensory axon that enters the spinal cord through the dorsal root
The afferent sensory axon synapses onto a motor neuron in the ventral horn of the spinal cord; incoming signals result in firing at this synapse and excitation of the motor neuron
The motor neuron projects an axon that exits the spinal cord ventrally and that terminates on the homonymous quadricepts femoris muscle
Firing along the efferent motor fibre results in excitation and contraction of quadriceps femoris
The patient accidentally (reflexively) kicks the physician - ouch!
111
What are mechanisms that terminate trans-synaptic signalling
Enzymatic degradation of neurotransmitter
Neurotransmitter re-uptake by the pre-synapse
Passive diffusion of neurotransmitter
Neurotransmitter uptake into local capillaries
Neurotransmitter uptake by glial cells
112
The cell bodies of which neurons lie outside of the CNS?
sensory neurons
113
Which cellular organelles can be found in pre-synaptic nerve endings?
mitochondria
vesicles
114
organisation of the nervous system
CNS and PNS
CNS:
Brain and spinal cord
PNS:
somatic and visceral
1. Somatic nervous system: controls voluntary movement
contains:
- motor fibres: general somatic efferents
- sensory fibres: general somatic afferents, special senses
2. Visceral/ Autonomic nervous system: controls involuntary movement
Autonomic/visceral nervous system
1. sympathetic
2. parasympathetic
- motor fibres: general visceral efferents
- sensory fibres; general visceral afferents
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a CNS neuron is
a neuron that is entirely contained within the brain or spinal cord
- if any part of a neuron projects outside of the CNS, then it is a PNS neuron
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white and grey matter
white matter: mostly axons
grey matter: cell bodies (ortical layers or clusters of neurons = nuclei)
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folded surface of the cerebrum
ridg es = gyri
grooves = sulci
deep grooves = fissures
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what is the hindbrain split into
pons
cerebellum
medulla oblangata
119
what is the brainstem made of
the midbrain, pons and medulla oblangata
120
what is the forebrain made of
cerebrum, thalamus and hypothalamus
121
foreman
openings (holes) in the skull or brain structures that allow the passage of nerves, blood vessels, and cerebrospinal fluid (CSF).
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frontal lobe
parietal lobe
occipital lobe
temporal lobe
executive functions (thinking, planning, emotion, behaviour, personality, motor control)
sensory processing, arithmetic, spelling
vision
memory, language
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spinal nerves
31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal)
- the first spinal nerve emerges between the skull and vertebra C1
- C8 emerges between vertebrae C7 and T1
- spinal cord is shorter than the vertebral column - cauda equina
- lumbar puncture at L3/4
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ventricular system
- four ventricles and central canal
- filled with cerebrospinal fluid
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CSF
- made by chloroid plexus epithelium
- chloroid plexus is highly vascularised
- recycled into venous blood via arachnoid granulations
- drainage of CSF: drains out of foramen of luschka and magendie into the sub arachnoid space
functions:
1. buoyancy
2. protection
3. removal of waster products
4. growth and signalling factors
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meningeal layers
the cns has three layers of meninges:
1. the innermost pia mater
2. the intermediate arachnoid mater
3. the outermost dura mater
CSF leaves the ventricular system of the brain through apertures and is released into the space between layers one and two - the sub-arachnoid space
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pia mater
- protects the CNS
- a fine vascular membrane that allows entry of blood vessels into the CNS
- provides an impermeable layer for containing CSF
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arachnoid mater
- protects the CNS
- a cobweb like membrane that forms the upper limits of the sub arachnoid space
- closely associated with the dura mater
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dura mater
protects the CNS
in the skull, composed of two layers which separate in places to form sinuses carrying venous blood
surrounding the brain, the dura mater is closely attached to the periosteum of the cranium; surrounding the spinal cord it hangs loosely only attached at the foramen magnum
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circulation of CSF
1. produced by chloroid plexus
2. lateral ventricles
3. interventricular ventricles
4. third ventricle
5. cerebral aqueduct
6. fourth ventricle
7. foramina of luschka, foramina of magendie or central canal of spinal cord
8. subarachnoid space
9. arachnoid granulations
10. superior sagittal sinus
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Where is the most likely place for a CSF blockage?
cerebral aqueduct
132
what is the purpose of the cell cycle
to copy the genome and partition the copies equally between the daughter cells (uni and multicellular organisms)
to enable a multicellular organism to grow to adult size
to maintain the total cell number of an adult organism
to replace lost or damaged cells
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how do prokaryotes divide
- by binary fission
1. DNA attached to cytoplasmic membrane at the nucleoid
2. cell enlarges and DNA duplicates
3. septum forms
4. cell divides in two, DNA partitioned into each cell
5. cells separate
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which pathways must be coordinated in cell division of prokaryotes
1. replication of DNA (and the partition of the two copies)
- circular chromosomes of prokaryotes has one origin of replication (ori)
- two replication forks form at the origin; replication is bidirectional
- two identical copies of the circular chromosome
2. cytokinesis (cell separation)
- FtsZ is distributed randomly throughout the cytoplasm of the cell
- early step in bacterial cytokinesis is the formation of a ring of protein, FtsZ, on the inner surface of the cytoplasmic membrane at the future division site
- FtsZ ring contracts and separates
HOWEVER
- the cell cycle of rapidly growing bacteria is shorter than the time needed to copy DNA
- cell division takes 20 minutes, DNA replication takes 40 minutes
: this implies that some cells will not contain DNA because DNA replication cannot keep up with cell division
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paradox of replication in prokaryotic cells - what happens instead?
- resolved by DNA replication being initiated before completion of the previous round - this is multifork replication
- ensures that at least one round of replication is finished before cytokinesis
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eukaryotic cell cycle additional complications
1. genome is composed of multiple linear chromosomes (necessitating co-ordinated replication of all of them as well as their faithful segregation)
2. multicellularity: cells in the context of organs and tissues
3. numerous organelles (must partition into daughter cells)
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universal characteristics of the cell cycle
- DNA must be faithfully replicated
- replicated chromosomes must be accurately segregated
138
phases of the cell cycle
G1: growth phase, doubling the mass of organelles and protein, including synthesis of enzymes that will drive DNA replication
S: DNA synthesis phase, chromosome duplication
- at the end of S phase, each replicated chromosome consists of a pair of identical sister chromatids
- they must not be allowed to separate, otherwise bipolar attachment to the mitotic spindle would be difficult to achieve
- cohesin ensures they do not drift apart
G2: preparation for mitosis. the beginning of mitosis is marked by two events
1. chromosome condensation: condensin encircles loops of DNA and compresses the sister chromatids to give a compact structure
2. formation of mitotic spindle: a bipolar array of microtubules
- kinetochore: complex or proteins attached to the centromere
- the nuclear membrane must breakdown early in mitosis so that the spindle has access to the chromosomes
cytokinesis: once the sister chromatics have reached opposite poles of the cell:
- nuclear membrane begins to reform
- cytoplasm is divided in two by a contractile ring of filaments composed of actin and myosin II
- the contractile ring divides the cytoplasm from the outside in
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variations of the cell cycle from organism to organism
1. timing
2. early embryonic cycles: have division with no growth. somatic cells grow after each division
3. nuclear envelope dynamics:
- unicellular organisms operate a closed mitosis: the nuclear envelope remains intact
- multicellular organisms: open mitosis - nuclear envelope breaks down and then reforms
4. polarity: some cells divide asymetrically
140
aspects of cell cycle control
anchorage dependence: cells must be attached to a substratum in order to divide
density independent inhibition: in which cells stop dividing once they contact each other
141
the cell cycle control system:
1. the cell cycle engine: protein complex that drives the cycle
2. co-ordination
3. checkpoints: the cycle will stop if the cell is deprived of nutrients or DNA is damaged, or if chromosomes fail to attach to the spindle
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cell cycle engine
- phases of the cell cycle are driven by the action of a protein kinase, the cyclin dependent protein kinase
- levels of the kinase remain constant
- the activity of the kinase activates the phases of the cycle
- the kinase is only active when complexed with the protein, cyclin
- cyclins are the key to regulating the cell cycle
they
1. undergo cycles of synthesis and degradation
2. there are different CDK's and cyclins, each pair activating a different phase of the cell cycle
eg G1/S phase cyclin = cyclin E
M phase cyclin = cyclin B
- promotes entry into mitosis by activating condensin and inducing nuclear membrane breakdown
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checkpoints
- surveillance mechanisms operate to ensure next phase is not initiated unless the previous one is completed
1. In G1: restriction point (R). a positive signal (growth factor) from the outside will instruct the cell to divide
2. At G2/M: is DNA synthesis complete? cell cycle is suspended if not
3. spindle checkpoint: is each chromosome attached to the spindle?
4. DNA damage checkpoint: arrests cycle while damage is repaired
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co-ordination of the cell cycle
- phases of the cell cycle must occur in the proper order
- existence of mechanisms for this was proven using cell fusion experiments eg
1. fusing an S phase with a G1 phase cell:
- the S phase nucleus continues DNA replication
- the G1 DNA is instructed to enter S phase
2. fusing an S phase with a G2 phase cell:
- the S phase nucleus continues DNA replication
144
consequences of checkpoint failure
failure of DNA damage checkpoint:
- cycle keeps turning despite DNA damage and mutations accumulate
- leads to cancer
if spindle checkpoint fails:
- unequal segregation of chromosomes
- causes down syndrome
145
different modes of intercellular communication
1. endocrine via a hormone
2. paracrine via a local mediator
3. neuronal via a neurotransmitter
4. contact-dependent via a membrane bound signal molecule
146
different types of receptors for cell signalling
1. cell surface receptors: bind ligands with high selectivity and high affinity
2. intracellular receptors: receptor is either within the cytoplasm or the nucleus. cytoplasmic receptor: ligand complexes can translocate to the nucleus
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major membrane receptor families
ion channels
G protein-coupled receptors
enzymes
148
GPCR signalling at the membrane
1. signal binds to receptor, receptor undergoes a conformational change
2. heterotrimeric G protein associates with receptor
3. Galpha-GDP exchanges GDP for GTP
4. G protein dissociated into Ga-GTP and Gby subunits. Both subunits are abled to activate other proteins
5. Ga-GTP activated effector enzyme (adenylyl cyclase)
6. effector enzyme produces second messenger (cAMP)
7. Ga subunit (GTPase) hydrolyses GTP to GDP, Gaby complex re-associated, signal terminates
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cAMP
- a second messenger (messenger that amplifies the signal)
- derived from ATP
- inactivation by hydrolysis
- cAMP activates protein kinase A (PKA)
- PKA is heterodimeric - 2 subunits that are structurally and functionally different
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adrenaline response in muscle cells
- adrenaline binds to beta-adrenergic receptor (a GPCR receptor) in muscle cells
- GPCR signalling
- cAMP levels increase, activating PKA
- PKA phosphorylates glycogen synthase, inhibiting glycogen synthesis
- increases glucose
- PKA also phosphorylates glycogen phosphorylase
- glycogen phosphorylase stimulates
- increase glycogen degradation = more glucose
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Which signalling factors bind to members of the G protein coupled receptor superfamily
Adrenalin, Acetylcholine, Retinal in photoreceptors
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why do cells need endocytosis
lipid bilayer is poorly permeable to ions and macromolecules
small and large molecules can enter through protein pumps, carriers or channels
macromolecules can enter only through membrane bound carriers = endocytosis
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endocytosis definition
the process of uptake of outside material by invagination of the plasma membrane followed by pinching off and intracellular vesicle formation
154
different types of cellular uptake mechanisms
macropinocytosis
clathrin-coated vesicle
noncoated vesicle
caveolae
phagocytosis
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phagocytosis
example
function
mechanism
phagocytosis of a yeast cell by a macrophage
ingestion/ removal of bacteria
- phagocytic cells have receptors that can bind antibodies that tag bacteria
- receptors that bind bacteria become activated
- activation of F-actin polymerisation
- plasma membrane protrudes and 'zippers' around particle and phagosome is sealed off
- F-actin disassembles
- phagosome is transported into the cell
- fuses with lysosome = phagolysosome
- degradation of content
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examples of pathogenic bacteria that induce their own phagocytosis to get inside mammalian cells
1 bubonic plague
2. listeria
3. shigella
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macropinocytosis
- function
- uptake of fluid for feeding and removal or large number of growth factors from plasma membrane
- growth factors stimulate actin driven protrusion of the plasma membrane called ruffles that are taken up as large vesicles
- can be triggered by some bacteria for uptake eg salmonella
- cancer cells use this for nutrient uptake
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clathrin mediated endocytosis
- function
- 2 types
- structure
- receptor mediated endocytosis allows the cell to take up specific macromolecules which are not abundant in the extracellular fluid via more than 25 different receptors
- requires clathrin and adaptor molecules
- constitutive receptor mediated:
iron uptake - tranferrin receptor
cholesterol uptake - LDL receptor
- ligand induced receptor mediated
modulation of growth factor signalling
example: EGF receptor
three legged structure - 3 light chains and 3 heavy chains
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clathrin mediated endocytosis: mechanism
1. coat assembly and cargo selection: adaptin recruitment
2. bud formation: adaptin recruits clathrin
3. vesicle formation: recruitment of dynamin, N-WASP = Arp2/3 = actin polymerisation
4. uncoating: HSC70 auxillin
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clathrin mediated endocytosis: dynamin
- large (100kDa) protein
- can oligomerise into spirals
- required for the fission of vesicles
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clathrin mediated endocytosis: role of F-actin polymerisation
- supporting role in vesicle scission
- transport of vesicle away from plasma membrame
162
caveolin mediated endocytosis
- caveolae: small 50nm invaginations enriched in cholesterol and caveolin
- caveolin self associated to form a coat and together with cholesterol in the membrane causes membrane invagination
- internalisation of caveolae required dynamin and F-actin
- now thought to function as a plasma membrane reservoir to balance membrane tension
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membrane traffic along the endocytic pathway: rab proteins
- rab proteins: regulate compartmental specificity
- Rab-GTP recruit motor proteins that transport carriers on actin filaments or microtubules
- Rab-GTP recruit effectors: targeting and docking components (eg SNARE's)
- Rabs and effector proteins are primary determinants of compartmental specificity
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membrane traffic along the endocytic pathway: SNARE's
- function
- mechanism and recycling
SNAREs are transmembrane proteins
recruited by Rabs and are specific for compartments
v-SNARES and t-SNAREs on opposing membranes form trans-SNARE complex
- conversion if trans-SNARE to cis-SNARE complex provides energy for fusion of vesicle with target membrane
- NSF, an ATPase dissociate cis-SNARE complex and recycles SNAREs
165
Which endocytosis mechanisms involve actin
phagocytosis
macroprinocytosis
receptor-mediated endocytosis
ligand-independent endocytosis
caveolin mediated endocytosis
166
What is the role of HSC70 during endocytosis?
It helps uncoat an internalised vesicle
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the cytoplasmic pathway
1. mrna attaches to cytoplasmic ribosome
2. protein completed and released in folded form to cytoplasm to make a cytoplasmic protein, be transported into peroxisomes or into the nucleus
3. or protein completed and released in unfolded form into cytoplasm. then transported into mitochondria where it folds
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the endoplasmic reticulum pathway
endoplasmic reticulum
transport vesicles
golgi
cis/trans golgi : faces towards and away from the ER
secretory vesicles fuse with plasma membrane and empty contents
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two possible destinations of the protein
- protein ends up in ER lumen or is transported further to other vesicular compartments or secreted from cell
- protein ends up embedded in membrane
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transport vesicles
- how do they fuse and empty their contents
- vesicle contains v-SNARE
- membrane contains t-SNARE
- SNARES fuse together to enable docking of the transport vesicle
- specificity of vesicular fusion to the plasma membrane is regulated by SNARE proteins
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protein modifications in the ER and the golgi
ER:
-protein folding - lumen of ER
- formation of disulphide bonds
- quality control - eliminated at the ER
Golgi:
- glycosylation by glycosyl transferases
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blood group antigens
glycosyltransferases = enzymes in golgi that add sugars to proteins
- humans have three different alleles of glycosyltransferases that glycosylate the proteins on the surface of red blood cells: O,A,B
OO = universal red blood cell acceptor
AB= universal plasma donor
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the lysosomal postcode
- mannose-6-phosphate added to proteins in the golgi
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lysosomal postcode disorder
inclusion cell disease = mucolipidosis
- autosomal recessive
- proteins fail to make it into lysosomes, are secreted instead
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4 possible destinations for proteins in the mitochondria
1. outer membrane
2. inner membrane space
3. inner membrane
4. matrix
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nuclear cytoplasmic trafficking
nuclear localisation signal: short and contains positively charged amino acids
importin
exportin
the small GTPase Ran couples export with GTP hydrolysis
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different forms of cell death
1. necrosis: traumatic cell death from acute injury
2. apoptosis: involves activation of a death programme/suicide
3. excitotoxicity: in neural tissue only
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necrosis vs apoptosis
causes
necrosis: injury/insult
- ischemia
- hypoxia
apoptosis: withdrawal of growth factors, chemotherapy, contact with cytotoxic T cells, following a developmental programme
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necrosis vs apoptosis
characteristics
necrosis:
- membrane damage
- chromatin flocculation
- energy levels rapidly depleted, leakage of cellular contents and inflammatory response
apoptosis:
- intact membrane with blebbing
- chromatin condensation
- energy levels maintained or depleted slowly, no leakage and no inflammatory response
- rapidly engulfed by phagocytes
blebbing: when the cytoskeleton separates from the cell membrane, causing spherical protrusions
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apoptosis follows a pre-determined path
1. chromatin condensation and membrane blebbing
2. cell fragmentation into apoptotic bodies
3. phagocytosis
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why cells commit apoptosis
1. during metamorphosis
2. elimination of cells that have served their purpose during development
3. cells infected by viruses
4. cancer cells
5. cells bearing excessive DNA damage
6. to promote self tolerance
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biochemical characteristics of apoptosis
1. DNA is cleaved by an endonuclease to give a ladder pattern when the DNA is resolved by electrophoresis
- fragmentation means that many new free ends of DNA will be generated: these can be detected by the TUNEL assay. the transferase recognised the free ends and adds dUTPS that are labelled with a marker
2. phosphatidylserine is exclusively located on the inner leaflet of the plasma membrane lipid bilayer: in apoptotic cells it flips to the outer leaflet and can be detected by annexin V
3. apoptotic cells lose the electrochemical potential that exists across the inner mitochondrial membrane - this change in membrane potential can be measured using fluorescent dyes
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externalised phosphatidylserine does what for cells...
- it is an 'eat me' signal
- attracts motile phagocytes
- receptors on the phagocyte bind to externalised phosphatidylserine stimulating...
1. the release of antiinflammatory cytokines
2. engulfment of the dying cell
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enzymes that drive apoptosis in multicellular organisms
caspases
- proteases with cysteine at the active site, which cleave their substances at specific aspartate sites
- eg ICAD
- found in all mammalian cells
- their premature activation is lethal
- robust mechanisms are in place to control activation including
1. synthesis of caspases as inactive zymogens
2. highly evolved upstream regulatory pathways including the presence of endogenous inhibitors
183
examples of caspase targets
1. structural proteins eg lamins and gelsolin
- cleavage of lamins leads to nuclear shrinkage and fragmentation
184
two apoptotic pathways
1. extrinsic
- responding to extracellular signals
- involves transmembrane death receptors which are members of the tumor necrosis factor receptor superfamily
- also called the death receptor pathway
2. intrinsic
- apoptotic stimuli cause mitochondrial membranes to become leaky, leading to release of cytochrome c into cytoplasm. cytochrome c activates caspase.
- also called the mitochondrial pathway
- responsive to
1. cytotoxic drugs that have entered the cell
2. dna damage
185
damage caused by UV irridiation
- UV-B is the major mutagenic factor of sunlight
- induces chemical bonds between adjacent thymines, distorting DNA and causing problems in DNA replication leading to point mutations
- DNA damage leads to UVB-induced apoptosis which limits the development of skin cancer
186
what does excessive and insufficient apoptosis lead to
excessive:
-heart attacks and strokes can feature loss of cells by apoptosis
- type one diabetes mellitus: underlying cause is apoptosis of pancreatic b cells
insufficent:
- autoimmune diseases are characterised by large numbers of lymphocytes in spleen and lymph glands. stimulating the loss of these cells by apoptosis could limit the extent of the reaction against the individuals own tissues
187
excitotoxicity
when excessive glutamate acts on an excitatory receptor and causes cell death
- this is due to an increase in intracellular ca2+
188
why is prolonged activation of receptors dangerous
1. glutamate binds to NMDA and AMPA
2. activated AMPA receptors allow Na+ to enter the cell, depolarising the plasma membrane
3. this dislodges Mg2+ from the NMDA receptor, permitting entry of Ca2+
4. prolonged exposure of glutamate leads to prolonged entry of Ca2+
5. leads to activation of Ca2+ dependent enzymes involved in breakdown of protein, phospholipids, nucleic acid. plus the activation of enzymes that lead to elevated levels of reactive oxygen species which also react with the above biomolecules
189
what can excitotoxicity lead to
stroke, trauma, epilepsy, and neurodegenerative disorders
190
how do germ cells form in development
- germline cells are specified and set apart in the early embryo
- functional sperm and egg cells are only produced in the adult
- egg and sperm cells derive from germ cells
1. primordial germ cells first seen in proximal epiblast pre-gastrulation
2. during gastrulation they migrate to the posterior end of the embryo
3. PGCs then migrate to the gonads
- PGC tend to express a different set of genes to somatic cells
- migration controlled by chemical signals
4. PGCs enter the hindgut endoderm and then migrate via the dorsal mesentery to reach the genital ridges and differentiate into eggs and sperm
191
why do PGCs not remain in initial location
- to exclude them from the process of laying down the body plan
- a way to select healthiest ie those that survive migration
192
how does meiosis ensure that gametes have the correct amount of genetic material
- germ cells undergo meiosis: gametes with half the number of chromosomes are produced, therefore the zygote will have the correct number of chromosomes
- meiosis has two cell divisions: chromosomes are replicated before the first cell division but not before the second so the number is reduced by half
- prophase: replicated homologous chromosomes pair up and undergo recombination
193
oogenesis
- germ cells undergo some mitotic division as they migrate to the ovaries and continue to divide in the ovary
- once meiosis begins, primary oocytes arrest in prophase
- the first meiotic division not completed until after ovulation in the adult
- second meiotic division after fertilisation in the oviduct
- polar body: small cell which is a product of meiosis during the development of the egg, contributes to parthenogenesis
194
spermatogenesis
- germ cells enter the embryonic testis where they will become sperm; arrest at G1 stage of the cell cycle
- after birth, they divide by mitosis, forming a population of stem cells (spermatogonia)
- spermatogonia stem cells give rise to differentiating spermatocytes which undergo meiosis giving rise to spermatids that mature into fully developed sperm
195
hypotheses to explain mammalian fetal ovarian germline death
1. apoptosis is actively suppressed by growth factors which act through receptors that are expressed on the germ cell surface
2. failure of meiotic recombination results in germ-cell death by defect
3. in germ cell cysts that form during development, 'nurse' germ cells transport macromolecules and organelles into one germ cell, which is destined to become the oocyte
196
how does fertilisation occur in mammals
fertilisation: fusion of the egg and sperm to initiate development
- occurs in the fallopian tube
look at pics
197
structure of human sperm
acrosome: enzymes to digest protective coat around the egg
plasma membrane: proteins that bind to egg and facilitate entry
flagellum: movement
mitochondria: energy
once sperm are deposited in the female reproductive tract, they undergo capacitation which facilitates fertilisation
capacitation: membrane remodelling and removal of certain inhibitory factors
198
fertilisation of a mammalian egg
1. sperm penetrates sticky layer of hyaluronic acid and somatic follicle cells - cumulus cells
2. sperm binds to zona pellucida
3. penetrates the zona pellucida - layer of fibrous glycoproteins via acrosomal reaction
4. plasma membrane of sperm fuses with egg plasma membrane
5. sperm nucleus enter the egg cytoplasm
199
calcium wave at fertilisation
- makes the outer layer of the egg harden, preventing other sperm from entering
- fertilising sperm triggers wave
- calcium needed for the fusion of cortical granules with the cell membrane
200
cortical granule exocytosis
- due to high conc of Ca2+, cortical granule membrane fuses with the egg membrane
- contents of cortical granules released into space between cell membrane and vitelline envelope
- enzymes from cortical granules harden the envelope and release sperm bound to it
201
parthenogenesis
- development of an embryo from an unfertilised egg cell
eg in the development of komodo dragon and female and male honey bees
bees:
- they have a haploid-diploid sex determination system. females are produced sexually from fertilised diploid cells, and males arise from unfertilised haploid eggs
202
What do the cortical granules of the egg cell contain?
hyalin
203
stem cells are non specialised cells with which two characteristics
- can self renew
- can differentiate
204
characteristics of stem cells provide us with the potential to:
1. understand early human development
2. understand control of cell division
3. cell based drug screening platform
4. cell based therapies
- replace damaged cells for treatment of diseases such as parkinson's
- reduce need for organ and tissue donors/transplants
205
embryonic stem cells
- where do they come from
- how to study them in the lab
- come from the inner cell mass of the blastocyst
- can be grown indefinitely in the lab
- have the potential to generate all cell types (pluripotent)
- differentiation can be controlled in culture to generate specific cell types
206
how do we ensure that cultured cells are embryonic stem cells
- inspect cells through a microscope to see if they look healthy and undifferentiated
- ensure that the cells are capable of long term self renewal
- ensure they are genetically normal via karyotyping and expression of pluripotency markers
- ensure the cells can differentiate
207
tissue stem cells
- generated from ES cells
- multipotent
- generate tissues of the body during development
- can be grown in the lab
- includes stem cells isolated from fetal and cord blood
- retained in adult tissues where they are involved in repair and replacement
208
what can tissue stem cells form
1. haematopoietic stem cells: isolated from blood or bone marrow
2. mesencyhmal stem cells: isolated from the bone marrow
3. neural stem cells
209
two neurogenic regions in the adult brain
1. subventricular zone lining the lateral ventricles
- neurons formed here involved in sensory info associated with olfaction and memory
2. subgranular zone of the hippocampal dentate gyrus
- neurons formed here are involved in spatial awareness, pattern separation, cognitive flexibility, mood
210
the stem cell niche
microenvironment around stem cells that provide support and signals regulating self renewal and differentiation
- anchor the stem cells and factors secreted by niche cells concentrating them and presenting then to the stem cells
- blood vessels that carry nutritional support and systemic signals to the niche from other organs
- neural inputs promote the mobilisation of cells out of the niches
211
current applications of stem cells
- tissue stem cells = treat blood diseases and burns
- umbilical cord stem cells = leukaemia in children
- limbal stem cells = repair corneal damage
- iPSC = age related macular degeneration
212
iPS and ES cells can also be used for
organogenesis
213
What are the core pluripotency factors?
KLF4, C-MYC, OCT4 and SOX2
214
the immune system represents a number of surveillance mechanisms:
how does it do this?
1. responds to infection by microorganisms
2. helps repair damaged tissues
3. helps slow cancer development
- the system is capable of recognising self vs non self
- can secrete protective substances into bodily fluids (humoral immunity)
- can launch a cellular response (cellular immunity)
215
mechanisms which protect the body before the immune system is invoked
barriers: both physical and chemical in nature
- the skin, mucous membranes and cilia are examples of physical barriers
- chemical barriers include mucous and the acidic properties of the stomach
- surface epithelia can secrete microbicidal substances eg lysozyme and phospholipase in saliva and tears, and cryptidins and defensins in the gut
- blood also contains antimicrobial substances
216
the 2 arms of the immune system
innate immunity
adaptive immunity
217
innate immunity
- non specific
- rapid
- response to infection
- response to altered self
- can be humoral
- can be cell mediated
218
adaptive immunity
- specific
- slower to develop
- response to infections and altered self
- can be humoral or cell mediated
- has memory
219
cells of the innate immune response
macrophage and neutrophil
- highly phagocytic
- contain lysosomal and microbiocidal proteins which destroy engulfed bacteria, cellular debris or foreign particulate matter
- neutrophils die after having disposed of their target
- macrophages can produce new lysosomes and continue to engulf and destroy foreign material
220
macrophages
- can reside in a tissue or wander and survive for several weeks or months
specific names in certain locations
1. liver = kupffer cells
2. bone - osteoclasts
3. kidney = mesangial cells
4. brain = microglia
- also found in the lung, lymphoid organs and connective tissue
221
adaptive immune cells: lymphocytes
- make up 30% of WBC population
- different classes
1. B cell
2. T cell
- circulate in the blood and lymph and because activated in secondary lymphoid organs
222
B cell vs T cell
B cells
- arise in bone marrow
- mature in the bone marrow
- activated in secondary lymphoid organs
- secrete antibodies specific to the target antigen
- long term immunity maintained by memory B cells
T cells
- arise in bone marrow
- mature in the thymus
- activated in secondary lymphoid organs
- activated to induce a cell mediated adaptive immune response
- long term immunity maintained by memory T cells
223
T cells
- direct and recruit other cells of the immune system, as well as attacking diseased cells directly
- specific T cell receptors are responsible for recognition of the antigen
Four Subsets:
1. helper T cells: can activate B cells
2. cytotoxic T cells: specifically kill infected cells
3. regulatory T cells: help modulate responses
4. memory T cells
224
antigens
- substance that may or may not be harmful which activates the immune system
- can be a protein, carb or nucleic acid
- can induce a T cell or B cell response
224
B cells
- activated by antigen and helped along by T helper cells
- secrete antibody when activated
antibodies either
1. neutralise the pathogen
2. facilitate uptake by phagocytes (opsonization)
two subsets
1. plasma cells
2. memory cells
225
antibodies
- glycoprotein that interacts with a specific antigen
- can neutralise the antigen or coat it to induce phagocytosis by macrophages
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