Animal and Human Cell Biology Flashcards
What does the plasma membrane contain?
Specific proteins, lipids and sugars, identified from fluorescent microscopy
What does the plasma membrane do?
Surround the cell
What are phospholipids?
Amphiphatic and make biomembranes
in the presence of water, phospholipids assemble to make a lipid bilayer
What affects membrane fluidity?
Steroids but also serve as hormones
Cholesterol reduces it at moderate temp and avoids solidification at low temp
Lipid composition also affects other features such as membrane curvature
What is cholesterol also used?
Vitamin D and hormoes
What is the idea of the fluid mosaic model?
Proteins swim in the lipid biolayer
Describe the plasma membrane
Fluid, plasma membrane of neuronal cell is pulled out with laser tweezers
What are lipid rafts?
membrane regions that assemble specialised lipids and proteins to perform a certain task
Transport across biomembranes
Semipermeable - uncharged and hydrophobic molecules can pass through the membrane, charged molecules cannot
Which proteins are embedded in membranes?
enzymes, receptors, cell-cell recognition, intracellular joining and attachment to extracellular matrix and intracellular cytoskeleton
Membrane potential
Channels cooperate to form a membrane potential over their plasma membrane
More positive charge outside and more negative inside
Non excitable i.e. epithelial cells don’t chain their potential but excitable ones can
What is membrane potential due to
difference in ion permeability of plasma membrane and the activity of the ion pumps
Establishing a resting membrane potential
Potassium leakage channel and sodium potassium pump
4 sodium ions pumped inside - 4 potassium and 7 sodium inside, 6 potassium and 1 sodium in, now potassium equal at 4 and 7 sodium inside and 1 outside
Cell to cell contact
Cells in epithelium establish tight lateral and basal contact
Resist forces, stick together to make sure there is no diffusion
What is a tight junction
Diffusion barrier, hold cells together, consist of plasma membrane proteins that interact, resisting liquid nature of the plasma membrane
What is an adherence junction
Consists of cadherin (bridge between cells) and catenin,(link to the actin cytoskeleton), appear to be involved in controlling actin organisation in epithelial cells, supporting strengthen and resistance against forces
What is a gap junction
Small channels, channels between the cells, each made of connexions, proteins cannot pass unless they are small, transport of ions, communication between cells, interacting very tightly
What is desmosome
Contain specialised Catherin proteins that interact with each other, stabilises the cell, resist shear force in epithelia and in muscle, linking to intermediate filaments
AS a bundle they can provide strength
Where are intemediate filaments not present?
In structures with a cell wall
Hemidesmosome
Half desmosome, don’t interact with another desmosome, they interact with the extracellular matrix, contain proteins including integrins, in skin epithelial cells, anchor epithelia cell to basal lamina
Extracellular matrix
fibres of secreted proteins (collagen, matrix proteins, glycoproteins), holds tissues together, provides strength directly cell migration
What do macrophages do?
Sniff the pathogen and hunt it down, find invaders
What happens when the actin on each cell interact?
They meet and internal reorganisation happens
A simple intracellular signalling pathway
Extracellular signal molecules, receptor protein, intracellular signalling proteins (kinases), effector proteins
Signalling via GTP binding proteins
G protein binds GTP, which binds either as GDP or GTP, GTP can be hydrolysed to GDP, ready to get a signal (2 phosphates)
GEF can change GDP to GTP
Switch this off GAP
Small monomeric G proteins -receive signals from many receptors
Large trimeric G proteins - activated by membrane integrated G protein coupled receptors
Protein Kinases
An enzyme that transfers phosphate groups from high energy donor molecules such as ATP to specific substrates through phosphorylation
Protein Phosphatase
An enzyme that removes a phosphate group from a protein through desphosphorylation
What controls protein activity?
Protein kinase and protein phosphate
How many kinases and phosphatases?
520 kinases and 150 phosphataases
Signalling via phosphorylation and desphorylation
Protein kinase signals on, protein phosphatase signals off, kinases form a signalling cascade
What do kinases do?
integrate info and act as microchips
Describe Cdk kinase
Has this phosphate been removed, has this phosphate been added, is cyclin present
YES= control of cell cycle progression
Describe Src-type kinase
Has this phosphate been removed, has this binding been disrupting, has this phosphate been added
YRS = control of regulate various biological functions
Cytoplasm what does it contain?
proteins and RNA, ribosomes - very dense
What is Brownian motion?
Put pollen grain into water and they flickered around due to random collisions of water molecules with the particle
DEScribe diffusion
not directed, larger objects do not diffuse, a need for active transport by molecular motors In the cytoskeleton
What are the subunits of ribosomes
70S (50 and 30) prokaryotes, 80S (60 and 40) eukaryotes
What is S
Svedberg Unit - sedimentation behaviour of particles, mass, density and shape will determine S
Ribosomes will travel based on centrifugation
developed a technique of analytical ultracentrifugation
What is translation?
matching tRNA to mRNA codon, release of elongation factor TU, formation of peptide bond, elongation factor G triggers a forward movement of ribosome
What is a translation elongation factor?
50s, 30s, confirmational change in ribosome might help walking along the mRNA in order to synthesis a protein, molecular ratchet
What is a polysome?
Numerous ribosomes operate along a single mRNA molecule, can be in the cytoplasm or on other membranes
What does the nuclear contain?
Euchromatin, heterochromatin, lamina, nuclear pore, nuclear envelope (double biomembrane)
Describe nuclear pores
Highly order multi protein complexes, eight fold symmetry, numerous proteins build the pore and control nuclear transport
What are nucleoporins?
proteins that make the nuclear pore
How is the nuclear pore kept in place
by binding to a network of fibres called the nuclear lamina, inside the nuclear envelope
What are the functions of nuclear lamina?
can cause disease, keeps the nucleus in shape, anchoring chromosomes in transcription and control, for animals only
What are the lamina that make the cage?
LaminB1, Lamina A/C, DIC and overlay
What happens to nuclear lamina in mitosis?
It disassembles, nuclear envelope disappears and chromosomes are exposed, nuclear lamina is tough to get rid of
Phosphorylation gets rid of lamina, then it is formed from dephospho rylation, fusion of nuclear envelope fragments
Describe the nucleolus
Forms ribosomes, granular component(ribosome assembly site), fibrillar centres (rRNA transcription), ribosomal proteins are imported into the nucleolus, Assembled ribosomes are released,
Heterochromatin
remains packed after mitosis, transcriptional inactive, 10% of DNA
Euchromatin
Transcriptional active
What results in chromatin
Chromosomal DNA is highly folded involving interactions with structural proteins
What happens to DNA in mitosis
tightly packed during mitosis by which DNA is inherited (condensing)
What are proteases?
Proteins that cleave other proteins
Describe histones?
positively charged proteins, 4 types, H2A, H2B, H3 AND H4
What are the types of RNA polymerase in eukaryotes
1: ribosomal RNA
2: mRNA
3: tRNA
What are the types of polymerase in plants
siRNAS for heterochromatin formation
What type of polymerase is in prokaryotes?
Just RNA polymerase
Describe transcription
Numerous transcription factors bind to the TATA box in the promoter
RNA polymerase binds to to the template strand to make a copy strand and the RNA is released
Where is transcription and translation occurring for pro and eu
Pro: cytoplasm, many genes on one mRNA
Eu: Nuclear, cytoplasm, one mRNA for one gene
Endomembrane systen
Nucleus, ER, Golgi, Lysosome, endosomal compartment, transport vesicles
Compartments of the endomembrane system that are connected by transport vesicles that serve material exchange such as lipids and proteins
Describe transport vesicles
Carry various cargo, very small e.g. synaptic vesicle, molecular motors move them within the cell via membrane trafficking
What are molecular motors
enzymes that use ATP to walk along the cytoskeleton
What are the 3 types of trafficking pathways?
Secretory, endocytic and retrival recycling
Secretory pathway
Nucleus, ER, Golgi, secreted to plasma membrane and some delivery to other organelles e.g. edosomes
Endocytic pathway
Things taken up, degration in lysosome
Control response to ligand by taking up receptors
Retrival
Recycling of molecules that control endocytosis and secretion
Electron microscopy tells us that the organelles exist
ER
membranous synthesis and transport organelle that is the extension of the nuclear envelope, membrane sacs and branched tubules which are motile
What are the two types of ER
smooth and rough
Describe the sER
Production of lipids and steroids, calcium storage, detoxification of drugs, metabolism of carbs
Describe the rER
processing of secretory proteins
Cotranslational translocation into ER
ribosome assembles and binds mRNA
If polypeptide contains a signal sequence its target to the ER membrane
The signal peptide is cleaved off and the protein is translated into the ER lumen where it is folded and further processed
Cytosolic proteins can contain signal sequences that target them to other organelles (nucleus, mitochondria, peroxisomes, chloroplasts)
Golgi apparatus
disc shaped stack of membranes, receives vesicles as cis and releases through trans
Oligosaccharide
provide protection against pathogens, serves in cell-cell recognition and signalling, marks progression of the protein, helps folding and interaction with other proteins
Where are oligosaccharide chains processed?
in the Golgi - most proteins that arrive at cis Golgi contain a N-linked oligosaccharide- in Golgi the chain undergoes a stepwise process in different cisterna
Endosomal compartment
Endosomes are part of the endocytic pathway, sends for recycling or for degradation
What are the 3 types of endoscopes?
early, recycling and late endoscomes
What fuses with the lysosome?
late endosome
Membrane trafficking along endocytic pathway?
formation of a vesicle at the plasma membrane
Fusion of vesicle with early endoscome
degradation or recycling
recycling via recyling endoscome (pH of 6.8)
Maturation of early endoscope to late endosome (pH of 5.5)
pH decreases to pH 4.5
recycling from late endoscope to Golgi
maturation of late endoscope into lysosome (pH of 4.5)
Lysosome
Vacuole, disposal container, pH of 5 - acid hydrolyses e.g. proteases, lipases
What are the pathways for degradation in lysosomes?
Phagocytosis, endocytosis, pinocytose
autophagy
Phagocytosis
in macrophages cleans the body from invading pathogen and damaged cells
some pathogens stop the process and escape the phagosome to infect the host cell
incomplete - underlies the endosymbiont hypothesis
Pinocytose
uptake of salt proteins and molecules
Autophagy
cell death, enclosure of cytosol and organelles into an autophagosome, organelles have a limited life time
Under starvation the cell recycles cytosol by autophagy
Peroxisomes
single membrane bound organelles that contain many enzymes, they are motile, made in endoplasmic reticulum, 50 different enzymes
How are peroxisomes made?
From endoplasmic reticulum, precursor vesicle, growth by uptake of cytosolic proteins and lipids, they split by fission to produce peroxisomes
What are peroxisomes useful for?
Digesting fatty acids
Describe detoxification of peroxisomes?
generates hydrogen peroxide which degrades by catalase
What do glyoxysomes?
in plant seeds convert fats into sugar by glyoxylate cycle
Lipid droplets
vary in seize and are enclosed by a monolayer, lipid bodies are fat storage droplets
What is a triacylglycerol
Fatty acids and lipid
What is a nucleomorph>
DNA containing relict of an engulfed eukaryote
How are lipid droplets made?
made at ER, in-between the bilayer
FABP makes fatty acid water soluble, shield the fatty acid by binding it in a hydrophobic pocket
Transport vesicles
Travel between compartments and plasma membrane, packed with proteins 50 types of integral proteins vSNAREs is most prominent
What is membrane specificity provided by?
SNARE receptors, vSNARE matches to a t-SNARE
Transport vesicle mattches to early endosome
Fusion of a vesicle with target membrane
Tethering, docking, fusion
What are the coats for transport vesicles?
Clathrin, COPI, COPII
How is the clathrin coat formed?
Cargo, cargo receptor and adaptin, 3 heavy chains and a light chain
What is a cargo molecule?
anything that needs to be endocytosed
What type of a vesicle is the transport vesicle?
Naked as the coat gets rapidly lost and interacts with cytoskeleton for intracellular transport
Extracellular vesicles
Transport vesicles released and are found in body fluids, urin, blood, fluid around brain and spinal cord
contains RNAs and proteins provided by donor cell
Deliver their content to recipient cells
Extracellular vesicles interact with the target cell in various ways
Interact with the cell surface - stimulation of target cell, membrane receptor transfer
Deliver material to the cell - protein delivery and reprogramming of target cell
What can spread cancer?
Extracellular vesicles
Ectosomes (microvesicles)
formation at donors plasma membrane, transfer proteins, mRNAS and miRNAS uptake via fusion with plasma membrane
Exosomes
Formed at early endoscopes released from late endoscopes, transfer proteins, mRNA and miRNAs, uptake via endocytosis or fusion with recipients plasma membrane
Overview of extracellular formation pathways
CVV delivered to early endosome, go to MVE to exosomes and go off or can go to lysosome for degradation
Function in cell to cell communication of
trigger intracellular cell signalling, immune responses, modifying enzyme activity, control of neutron function and blood vessel formaiton
Define the cytoskeleton
consists of filamentous bio polymers (microtubules, F actin and intermediate filaments) and associated proteins that are modulating the activity, dynamics or organisation of the cytoskeleton (actin binding or microtubule binding protein i.e. molecular motors)
Describe skeleton of cytoskeleton
connects all parts of cell, supports motility and helps spatial organisation
What are the three classes of filaments make up the cytoskeleton?
F-actin( short range transport, cell migration), microtubules(long range transport, chromosome inheritance) and intermediate filaments (mechanical strength)
Which filaments are part of the trafficking?
F-actin and microtubules as molecular motors do not go along intermediate filaments
What do intermediate filaments interact with?
desmosomes
What does the cytoskeleton provide?
tracks for intracellular trafficking, stability to the cell
What types of actin are there
Actin bundles for when a cell relaxes, F actin and actin monomers
What is actin
binds ATP , globular protein, G-actin is the block protein, protofilament- pearls string of G-actin
How does actin exist?
as monomers and as polymers
What end of actin grows the fastest?
plus end
What end of actin grows the slowest?
Minus end
What are the proteins in actin that control the change from G to F actin?
Cofilin (polymerising), profilin (depolymerising), thymosin (recycling)
ADP to ATP G actin
G actin is kept in an actin pool
Treadmilling of actin
filaments fold, protein stables and cell moves forward
lose subunits in the rear and whole thing moves forward
Where is actin added?
plasma membrane, plus end
How is F-actin organised?
Actin binding proteins, order bundling, dynamic cross linking and cross linking
What does actin form?
Cellular protrusions
Microtubules
Around nucleus, form extended fibres, alpha and beta tubules Dimers form protofilaments Anti polymerisation Bind to GTP 13 protofilaments Dynamic Forward backward Tubulin is added and released at one end of the polymer
Describe the dynamic nature of microtubule
Polymerisation - GTP bound tubules dimers added to plus end, a cap of GTP-tubulin stabilises the growing microtubule
Pausing - GFP to DFP tubules through hydrolysation
Depolymerisation - microtubule becomes unstable and depolymerises in a transition state called a catastrophe
Polymerisation - GTP tubules can bind the shrinking microtubule and establish a new cap called rescue event, microtubules switch between growth and shrinkage
What happens at plus end of microtubules?
Growing and shrinking
Beta tubules is exposed to the plus end
Dynamic behaviour
Extend to cell periphery
How do you see the dynamic behaviour of microtubules and F actin
Speckle microscopy
Incorporation of few GFP labeled monomers results in patchy fluorescence
What is the difference in dynamics between F actin and microtubules
Microtubule ends are dynamic while incorporated tubules remains stationary
F-actin incorporated actin treadmills through the actin filament meshwork
What do MAPs do?
stabilise tracks
What do plus end binding proteins do?
Control the dynamics of microtubules and participate in intracellular motility
attachment of microtubules, control of microtubule and of intracellular trafficking by regulating dynein
Microtubule minus ends
Concentrated near nucleus, centrosomes that contain centrioles
Similar to flagella
Holds nucleating proteins
Describe centrioles
consist of microtubules, become basal body of flagella and cilia, organise the PCM and ensure its inheritance
most fungi don’t have centrioles
Mother and daughter centriole - not membrane bound
PCM contain gamma tubules ring complexes which nucleate the microtubules
What is gamma tubules?
not part of microtubule but part of the nucleating site but is similar to alpha and beta tubulin
Intermediate filaments
Lose mesh work, not the same dynamic behaviour
made of mainly proteins in different parts of the body
But support mechanical strength
Share a coiled coil consisting of alpha helixes which are amphiphatic (charged at one side)
Broad range of coiled coil protein subunits assemble to make them
no ATP or GTP but they self assemble
only in animal cells
can disassemble into subunits to allow movement
What molecular motors are microtubule associated?
Kinesin and Dynein
What molecular motor is associated with actin?
Myosin
What do molecular motors do?
Walk along the cytoskeleton
What are minus molecular motors?
dynein
What are plus molecular motors?
kinesin and myosin
What is the common feature of all eukaryotic cells?
Cells gather material from the environement and duplicate
What are the characteristics of a channel?
It allows passage of molecules in and out and it can be gated
Which are the pathways that deliver material to the lysosome for degradaton?
Endocytosis, autophagy and phagocytosis
What do molecular motors do?
transport cargo along the fibres of the cytoskeleton
mechanical-enzymes
Which molecular motor is needed for Golgi?
dynein
Motor tool box in eukaryotic cells
Molecular motor are large protein complexes that hydrolyse ATP or GTP in order to walk along fibres
How can you prove that motors are mechanical enzymes
Glass slide and coverslip
Pipette myosin molecules, flushed under coverslip, other proteins are washed through with BSA wash
shows actin filaments and add ATP and the motor head moves the actin filament
Use fluorescent microscopy
How are motors recycled?
Kinesinand dynein bind to the same cargo, active in transport
How are collisions avoided
Dynein has the ability to change protofilaments while it moves so it can go lateral, kinesis cannot so two kinesin causes a problem
What is responsible for Intracellular membrane trafficking
Motors
What keeps the cell alive?
motility in neutrons by axonal transport, connects synapse with cell body
Synapse has to communicate with the cell body to keep the neurone alive
Neurons ahne to cope with long distances so axonal transport helps this
Anterograde
- to +
Retrograde
+ to -
