Cells Flashcards
5 kingdom classifications of life?
Plantae Fungi Animalia Protista Prokaryotae
Classification mainly based on morphology
3 domain classifications of life?
Bacteria
Archaea
Eukaryota
What are eukaryotic cells and what are prokaryote?
Eukaryote: Plants Animals Fungi Protoctisa
Prokaryote:
Bacteria and Archaea (both are monera)
Organisation of a bacterium?
Pilli Cell wall Plasma membrane Cytoplasm Nucleoid (DNA) (so no nucleus) Ribosomes Flagellum
Organisation of a eukaryotic cells?
Plasma membrane Golgi apparatus Peoxisome Mitochondrium Lysosome Enoplasmic reticulum Nuclear membrane Nucleus
Only cell that doesn’t have cell wall?
Animals
What extra do plants have?
Vacuole
Cell wall
Chloroplast
What extra do fungi have?
Cell wall
What is larger pro or eukaryote?
Eukaryote by far, also more complicated so theory that they developed after prokaryotes
A catalytic RNA molecule is called a?
Riboenzyme
Evidence RNA earlier than proteins?
RNA makes protein
RNA fundamental part of ribosome, whereas protein have just been added
How were the building blocks or RNA generated?
Random early earth conditions (eg lightening)
What could ribonucleotides bind together to form?
Replicase ribozymes which could make new replicases after polymerising on a clay surface
So can duplicate, due to temperature changes
How was a the lipid bi-layer in a cell made?
In Geysers, minerals catalyse the formation of fatty acids from hydrogen and carbon monoxide
Which have one end which hydrophilic (outside) and one is hydrophobic (inside) in a droplet known as micelles
Vesicle formation triggered by acidic pH or clay surfaces
What then occurs within the vesicle to from a protocell?
Flipping of fatty acids could bring in molecules, so they accumulate within the vesicle
The RNA replicase uses ribonucleotides to make a copy of another RNA replicase
Micelles fuse with the vesicle and enlarge it until it becomes unstable and divides
Random mistakes could lead to better replicases which could make protocol grow and divide faster
Protocell competes for resources driving evolution
What is the optical resolution limit and what does it rely on?
Minumum distance that allows recognition of object details
The optical resolution depends on the wave length of the light/beam used (smaller wave length = better resolution)
Features of light microscope?
Visible light ( wave length 390-700nm)
Glass lenses focus light
Resolution limit is 200 nm
Advantage is cells alive
Features of electron microscopy?
Electron beam ( wave length 0.0025 nm)
Electromagnetic lenses focus beam
Resolution limit 0.05 nm
Advantage is high resolution
Difference between scanning electron microscopy (SEM) and Transmission electron microscopy (TEM)?
SEM:
Electron beam scans over surface of sample
Can produce 3d images
Image shown on monitor
TEM:
Electron pass through THIN sample
Samples specially prepared
2D image shown on fluorescent screen
What is freeze fracture electron microscopy?
Freeze cell in resin, cut in half and analysis
What is averaging in microscopy?
Averaging many images together allowing reconstruction of the ultra-structure
What is fluorescence?
The emission of light by a substance that has absorbed light
The emission will be at a higher wavelength than excitation (the initial light), energy is lost before light is emitted
Allows visualisation of single molecules
What is GFP?
A reporter to analyse proteins in the living cell
It fuses to the DNA which will make the protein - which are normally still functional
These proteins are transcribed
They are exposed to blue light and will appear green
Different colours discovered so can observe interactions between different proteins
Also quantitive information as brightness represents how many there are
Advanced use of fluorescent proteins
FRAP (fluorescent recovery after photobleaching):
High energy sent in, which photobleaches the gfp molecules so can’t reflect light, if molecules are moving they will move into it and it will light up again, if not then nothing is moving
FLIP Fluorescent loss in photobleaching:
Used to see if one protein moves to another, so photo bleach, and then see if this photo bleach area appears in the place we think it will move
Photoactivation (photo-activatble GFP):
400nmlaser light induces a chemical reaction
About 100 fold increase in fluorescence after photo-activation
So allows you to identify the proteins you want to, as they will give lots of light off as their gfp has been activated
Features of plasma membranes?
Contains specific proteins, lipids and sugars
Surrounds the cell
Phospholipids are amphiphatic (hydrohphillic and hydrophobic) and assemble into bio-membranes in the presence of water
Fatty acid tails are hydrophobic, phosphate groups are hydrophilic
Cholesterol reduces membrane fluidity at moderate temperature and avoids solidification at low temperature (Temperature buffer)
Cholesterol also serves as a hormone
What’s a lipid raft protein?
Membrane regions that assemble specialised lipids and proteins to perform a certain task (Normally show reduced fluidity)
Types of protein in plasma membrane?
Transporters
Enzymes
Receptors
Cell-cell recognition
Intracellular joining
Attachment to the extracellular matrix and intracellular cytoskeleton
What does bio-membranes being semipermeable lead to?
Uncharged and hydrophobic molecules can pass through the membrane
However charged or polar cannot pass, so require a mechanism to get in and out
Such as protein channels, which can be open or gated
Also can go through via facilitated diffusion (protein changes shape not let molecule through, it can’t go back and no ATP needed
Pumps can pump molecules through requires ATP
4 types of gated channels?
Voltage
Mechanically
Temperature
Ligand
What charge is in the inside of the membrane normally and how is it created?
-50 to -70mV
SOPI pumps, and leakage channels
Example of non excitable and an excited cell?
Epithelial
Muscle cells and neurones
What do cells in an epithelium establish?
Tight lateral and basal contact to withstand friction
Tight junctions are formed hold membranes of the cells together, functions as a diffusion barrier, and consists of plasma membrane proteins that interact
There are also here’s junctions, consists of cadherin and catenin, cadherins bridge between the cells, catenins link to the actin cytoskeleton, they both control actin organisation
Gap junctions allow diffusion from cytoplasm of one epithelial cell to another, made up of connexins
There are desmosomes, contain specialised Catherine proteins that interact with each other and with intermediate filaments, they resist shear force in epithelia
They are hemidesmosomes which contain man proteins that interact with the extracellular membrane, they anchor the epithelia cell to the basal lamina ( extracellular matrix underneath the epithelium, probably also used in signalling
Extracellular matrix is fibres of secreted proteins, and they hold tissue together, provides strength and directing cell migration
Describe a simple intracellular signalling pathway?
Extracellular signal molecule
Receptor protein, on plasma membrane of target cell
Intracellular signalling molecules released, either will be via phosphorylation of proteins by protein kinases and phosphatases, or signalling by GTP-binding proteins
Effector proteins:
Metabolic enzymes - altered metabolism
Gene regulatory protein - altered gene expression
Cytoskeleton - altered cell shape or movement
Describe signalling via GTP-binding proteins?
G-proteins are molecular switches
They are activated by a Guanine nucleotide exchange factor (GEF), and inactivated via a GTPase-activating protein(GAP)
Small monomeric G-proteins receive signals from many receptors
Large trimeric G-proteins interact with G-protein coupled receptors
What’s a kinase?
An enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates
Process is known as phosphorylation
What are phosphatases?
An enzyme that removes a phosphate group from a protein, a process called dephosphorylation
What can occur to protein kinases for the signal to be amplified and spread to other pathways?
Get phosphorylated themselves
Creates signalling cascade
Function of Cdk kinase?
Control of cell cycle progression
Function of Src-type kinase?
Control or regulate various biological functions
What do the particles and molecules undergo in cytoplasm?
Brownian motion - flickering movement due to collisions
What does diffusion in cytoplasm depend on?
Size of the molecule/organelle
Smaller they are the more they move
Diffusion is very limited to larger objects as it’s too crowded
Features of ribosomes?
Consist of 2 subunits (small and large) made from ribosomal RNA and proteins
Prokaryotes have 70 S (smaller)
Eukaryotes have 80 S (larger)
S (Svedbery value) stands for sedimentation rate of a particle - depends on mass density and shape
Translate information from mRNA into proteins
Basic steps of protein translation?
Matching tRNA to mRNA codon
Release of elongation factor
Formation of peptide bond
Elongation factor G triggers a forward movement of ribosome
What is a polysome?
Numerous ribosomes operating along a single mRNA molecule
What is the nucleus linked to?
The endoplasmic reticulum
Parts of the nucleus?
Euchromatin
Heterochromatin
Lamina
Nuclear pore
Features of nuclear pores?
have 8 fold symmetry
Made up of numerous proteins and control nuclear transport
Made up of nuclearporins
Gated, control what goes in and out
What goes in and out of the nucleus through the nuclear pores?
In (import):
Proteins
Out (export):
Proteins
RNAs
Ribosomal subunits
What happens to the nucleus during mitosis?
It releases its content so has to re-import it’s nuclear proteins
Also the nuclear envelope and the nuclear lamina disassemble:
Phosphorylation of lamins - breakdown
Dephosphorylation of lamina
Fusion of nuclear envelope fragments
Fusion of enveloped chromosomes
What’s the nuclear lamina and it’s functions?
Forms a network at the inner nuclear membrane
Consists of intermediate filaments (cytoskeleton)
It organises chromosomes and supports transcription of genes
Also anchors nuclear pores and prevents clustering
What does the nucleolus do?
Forms ribosomes
Contains granular components which is the ribosome assembly site
Contains fibrillar centres where rRNA transcription occurs
Ribosomal proteins are imported into the nucleolus, the assembled ribosomes are then exported into the cytoplasm
It’s not membrane bound just a gathering of material
DNA associates with proteins into?
Chromatin
Features of DNA in the nucleus?
Heterochromatin:
- Remains packed after mitosis
- Transcriptionally less active
- 8% of DNA
- 2 types
Consecutive Heterochromatin - Always packed, non-coding DNA near centromere and telomers)
Faculative heterochromatin - Variable between cell type and development stages
Then there is euchromatin which is 92% of DNA and transcriptionally active
When is all the DNA tightly packed?
Mitosis, makes it easier to transport
What does packing DNA require?
Being wrapped around positively charged proteins called histones
Organised into nucleosomes - which loosen during transcription
What does RNA polymerase 1 form?
rRNA
What does RNA polymerase 11 form?
mRNA
What does RNA polymerase 111 form?
tRNA
What does RNA polymerase in plants form?
siRNAS required for heterochromatin formation
Basic Principle of transcription?
Numerous transcription factors bind to the TATA box in the promoter (upstream of the gene)
RNA polymerase binds to the template strand and synthesises an exact copy of the coding strand (except thymines are replaced with uracil)
RNA is released, further processed and the released from the nucleus bound to RNA binding proteins
Do prokaryotes have a nucleus, and how does this make them different to Eukaryotes?
NO, so transcription and translation occur in the compartment, and many genes on one mRNA
Whereas in eukaryote transcription and translation are compartmentalised and, one mRNA per gene
What does the endomembrane system contain?
Nucleus Endoplasmic Reticulum Golgi apparatus Lysosome/vacoule Endosomal compartment Transport vesicles
All the compartments of the endomembrane system are connected by transport vesicles that serve material exchange
What do molecular motors do?
Transport vesicles and organelles within the cell, this is called membrane trafficking
They are enzymes that use ATP to walk along the cytoskeleton
What happens at membrane with transport vesicles?
Exocytosis or endocytosis
What is secretory pathway?
Going out of cell
What is the endocytic pathway?
Outside to a vesicle inside
2 types of endoplasmic reticulum?
Smooth (no ribosomes)
Rough (studded with ribosomes)
Function of smooth ER?
Calcium storage for signalling
Lipid synthesis
Detoxification of poisons
Metabolism of carbohydrates
What is the Golgi apparatus?
Disc shaped stack of membranes
Has Cis end which receives transport vesicles from ER
Trans end releases the secretory vesicles
What do oliogosacchardides do (sugar chains on membrane) and where are they processed?
Provide protection against pathogens
Serves in cell-cell recognition and signalling
Marks progression of protein
Helps folding and interaction with other proteins
Made in the golgi apparatus
2 ways oligosaccharides can be linked to proteins?
Asparagine (N-linked)
Threonine (O-linked)
3 types of endosomes which are involved in processing endocytose material?
Early endosome
Recycling endosome
Late endoscope
Describe endocytosis?
Formation of a vesicle at the plasma membrane
Fusion of vesicle with early endosome
Decision - degradation or recycling
If recycling - pH drop removes ligand, and the rest is taking out
Or Maturation of early endoscope to late endosome - which can send material to Golgi
Or Lare endosome could turn into a lysosome - this is degradation
Describe lysosomes ( can also be called vacuoles in certain circumstances)?
Serves as a disposal container
pH far lower in lysosomes due to acid hydrolyses such as proteases, and lipases creating small building blocks
pH is low due to H+ pumps, which requires ATP
3 pathways to degradation in lysosomes?
Bacterium taken up via phagocytosis, then broken down in the lysosome
Pinocytosis and receptor mediated endocytosis, small particles go to lysosome and are broken down
Autophagy, lysosomes break down own cytosol , eg if starved
What are peroxisomes?
Single membrane bound organelles that contain many enzymes
Major site of oxygen utilisation
Detoxification produces Hydrogen peroxide which is degraded by catalase
Play important role in lipid metabolism
What are lipid droplets?
Fat storage droplets
Vary in size and are enclosed by a monolayer
Associated proteins regulate the metabolism of the fat droplets
Created at the endoplasmic reticulum
What is a nucleomorph?
When algae have a DNA containing relict of an engulfed eukaryote
What does Fat-acid-binding protein (FABP) do?
Makes fatty acids water soluble
Features of transport vesicles?
Carry cargo
50 types of integral proteins
Membrane speciality is provided by SNARE receptors
Most common vesicle is v-SNARE
Steps of fusion of a vesicle with a target membrane?
Therthering:
Rab-GTP on vesicle binds to Rab-binding tethering factor on membrane
Docking:
V-snare from vesicle forms complex with tT-snare on membrane
Fusion:
Cargo is unloaded into membrane
Features of vesicles having a coat?
Clathrin coat
COP1 coat
COP11 coat
Different coats are specific for particular places in endocytic and exocytic pathways
Coat concentrates specific proteins in patches
Features of extracellular vesicles?
Transport vesicles released from cells
Found in body fluids
Contain RNAs and proteins provided by the donor cell
Deliver their contact to recipient cells
Features of micro vesicles?
500-1000nm diameter
Formation at donors plasma membrane
Transfer proteins mRNASs and miRNAs that control protein expression
Uptake via fusion with plasma memrbrane
Features of exosomes?
40-100nm diameter
Formed at early endosome, released from late endoscopes
Transfer proteins, mRNAS and miRNAS that control protein expression
Uptake via endocytosis or fusion with recipients plasma membrane
Functions of exosomes and micro vesicles?
In immunology
In blood
In CNS
In bone
Also can spread cancer
What provides tracks that link the regions of the cell?
Cytoskeleton
Definition of the cytoskeleton?
Consists of filamentous bio-polymers ( microtubules, F-actin and intermediate filaments) and of associated proteins that are modulating the activity, dynamics, or organisation of the cytoskeleton
Why is the cytoskeleton called this?
Connects all of parts of the cell
Supports motility
Helps spatial organisation
3 filaments that make up the cytoskeleton?
F-Actin - Short range transport, cell migration, 7-9nm
Microtubuli - Long-range transport, Chromosome inheritance (mitosis and meiosis), 25nm
Intermediate filaments - mechanical strength, 10nm
Types of actin?
Filamentous actin (F-actin) Actin bundles (stress fibres) Actin monomers (G=Actin pool)
Where do you find Microtubules?
Coming from the centrosome - microtubule organising centre, near the nucleus
Where do you find F-actin?
Gathered on One side of the cell
Where do you find intermediate filaments?
Everywhere in cell
Describe the structure of F-actin?
G-actin Protein subunits that forms 2 Protofilaments wrapped around each other
Structure of microtubules?
Have dimers which are made of Beta tubulin and alpha tubulin, which forms protofilaments which form microtubulus
Describe polymerisation of a microtubule?
GTP-bound tubulin dimers get added to the positively charged end (polymerisation)
A cap of GTP tubulin stabilises the growing microtubule
Describe pausing of a microtubule and what can occur after?
Stops growing as GTP-Tubulin cap has all been hydrolysed by tubulin behind forming GDP-tubulin + phosphate
Then a rapid depolymerisation will occur:
The microtubule becomes unstable, this moment is known as a catastrophe
However then polymerisation can occur again, GTP-tubulin can bind creating a new cap, this is known as a rescue attempt
The switch between growth and shrinking is known as dynamic instability
Why is dynamic instability useful?
Allows the microtubule to reorganise
How has speckle microscopy proven dynamic instability?
If label some tubulin with GFP then will appear in patches on microtubule
What do plus-end binding proteins do?
Control the dynamics of microtubules and participate in intracellular motility
What do animal centrosomes contain, and what do they do?
They contain centrioles and the PCM
Centrioles consist mainly of microtubule
Become the basal body of flagella and cilia
They organise the pericentriolar material (PCM) and ensure it’s inheritance
Fungi and plants do not have centrioles
Do centrioles replicate during the cell cycle?
Yes
What does PCM contain?
Gamma tubulin which nucleates (making) the microtubules
General function of intermediate filaments?
Providing mechanical strength and in organising cytoplasmic architecture
Interact with microtubules and F-actin
Structure of intermediate filaments?
Made up of protein subunits which form a coiled coil made up of alpha helices
alpha helices are often amphipathic (charged at one side) which serves protein interaction
Extra facts on intermediate filaments?
Only found in animal cells
Do not require ATP or GTP for assembly, but rather self assemble into an apolar filament (2 bind to each other due to being amphipathic
They can disassemble into subunits to allow cell movement
Have different types of sun units
What forms the nuclear lamina and what does it do?
Intermediate filaments
Lamina provides stability and organises the nucleus
Example of an intermediate filament?
Keratin - makes nails
Some intermediate filaments also determine the optical properties of the eye lens
What drives cell motility and examples?
Molecular motors which are mechanical enzymes (protein complexes that utilise ATP to walk along the cytoskeleton)
Microtubule associated:
Kinesin
Dynein
Actin associated:
Myosin
How do molecular motors move across cytoskeleton?
They walk
Antony van Leeuwenhoek is famous for?
the discovery of microbes using a simple microscope
According to the “RNA World Hypothesis, the protocell had the following features?
It was surrounded by a lipid-bilayer (a bio-membrane)
It contained ribozymes and RNA
Which of the following structures confer resistance against shear forces and thereby ”strengthen” epithelial tissues?
Desmosomes
Hemidesmosomes
Tight junctions
What does the nucleus contain?
Heterochromatin
Euchromatin
A nucleolus
Organelles of the endomembrane system communicate with each other by?
Transporting vesicles
What does the endosomal compartment consist of?
early endosomes
recycling endosomes
late endosomes
Lipid droplets are fat storage compartments that are generated at the?
Smooth ER
Fusion of transport vesicles with a target membrane involves?
tethering of the vesicle to factors in the target membrane
docking of the vesicle to the target membrane
What do motors take through the cell?
Vesicles and organelles
Principle how a motor works?
Weak binding
Tight binding due to ATP-binding
Hydrolysis and power stroke
Release of ADP and Pi
Which molecular motors walk towards the plus end, and which walk towards the minus end?
Plus:
Kinesin
Myosin
Minus:
Dynein
How are motors recycled?
For example Kinesin and dynein would bind to the same cargo on either side of it
Then Kinesin would take it to plus end, when it reaches there will flip over to other side and dynein can take it back
How are collisions between Kinesin and Dynein avoided?
Dynein can move to avoid the Kinesin, as can move to another protofilament on the track
Kinesin just moves forward
What is the motility in neurones known as?
Axonal transport - Dynein and Kinesin working together
What does skeletal muscle mainly consist of?
Myosin, and F-actin in sarcomers
What do thick filaments consist of?
Myosin 11
What do thin filament consist of?
F-actin (sandwich the thick filaments)
How is muscle contraction controlled?
Stimulus from neutron spreads over the plasma membrane of the muscle cell
Depolarisation of membrane releases calcium from the sarcoplasmic reticulum into the cytoplasm
Binding of calcium to the troponin complex releases the bloke of the myosin binding site on actin
Myosin binds actin and walks towards the Z-disk
Calcium is removed by calcium pumps and myosin releases the actin filament = relaxation of muscle
Features of cardiac muscle?
Spontaneous contractions
Same principle of skeletal just less ordered
Difference between flagella and cilia?
Flagella come in smaller numbers and move the cell, propellar like motion
Cillia are in larger numbers and have function in fluid and particle transport, back and forth movement
Describe the structure of a cilliim/flagella?
Axoneme - The core, made from microtubules
Basal body anchors them to the cell - formed from centrioles
What support the formation and function of the cilium?
Intraflagellar transport along the axoneme:
Kinesin-2 moves building material up
Dynein bring moves material back down
Ultrastructure of cilium and flagellum?
9 pairs of microtubules around edge but on is half attached
1 microtubule pair in the middle
Dynein (slides microtubules against each other- they have protein bridges so results in bending):
Radial spokes (like a bike)
Outer arm dynein
Inner arm dynein
What leads motility in cells?
Actin in treadmilling, so led by the actin side
Steps:
Extension of plasma membrane pushing it forward due to actin polymerisation
Adhesion so doesn’t spread out
Translocation of the body forward
De-adhesion
Process that heals wounds
What occurs in prophase?
Chromosomes condense
Nuclear envelope disrupts
Spindle is formed
What occurs in metaphase?
Microtubules make contact with chromosomes
Chromatids are positioned in one plane
What occurs in anaphase?
Microtubules and motifs pull on chromosomes
Chromatids move to the poles
Rapid elongation of the spindle
Formation of a contractile ring
What occurs in telophase?
Cell middle contracts and separates (cytokinesis)
The chromosomes decondense
The nuclear envelope is formed
3 types of microtubules in the organisation of the mitotic spindle?
Astral microtubules
Polar microtubules
Kinetochor microtubules
How can you test that microtubules are required for mitosis?
Use Nocodazole which is anti microtubule, and see that mitosis can no longer occur
2 mechanisms that microtubules provide the force for chromosome segregation by creating a polar ejection force?
1-
de/polymerization of microtubules
Exerts force on attached chromosome
2-
Molecular motors that act on the microtubules
What’s checked at different checkpoints?
G2 (entering M) - is all DNA replicated, is environment favourable
Metaphase (end of M) - Are all chromosomes attached to the spindle
G1 (entering S) - is environment favourable
How does cytokinesis occur?
A contractile ring localises the area of constriction, near the cortex at the end of anaphase
composed of actin, myosin 11, regulators and actin binding proteins
Main features of mitochondria?
Have a double membrane with inner membrane folds (Cristae) and their own mitochondrial genome
Use sugars fats and oxygen to produce ATP (power house of the cell)
Steps of energy generation in mitochondria?
Uptake of food molecules from the cytosol into the mitchondrial matrix
Oxidation of Acetyl-CoA into carbon dioxide (Citric acid cycle = Krebs cycle); Production of the electron shuttle molecule NADH
NADH transfers the electrons to the respiration chain at the inner membrane; electron flux is used to build up a proton gradient
Back-flow of protons drives ATP synthesis
Do mitochondria and chloroplasts have their own genome?
Yes
What is apoptosis?
Programmed cell death
Occurs in multi cellular organisms
Blocks are recycled after death
It’s triggered by cell damage, apoptotic proteins cause damage to the mitochondria, which release factors that activate the apoptotic enzymes
Features of viruses?
DNA or RNA that is protected by a protein coat (capsid)
1000 x smaller than a human cell
Extracellular form known as a vision
Intracellular form = replication of DNA/RNA to assemble virus
Infecting fungi = mycophaves
Infect bacteria = bacteriophage
They are not alive
They self assemble
What’s a naked virus?
Protein coat (capsid)
Nucleic acid (RNA or DNA)
Enzymes (not always)
What’s an enveloped virus?
Protein coat (capsid)
Nucleic acid (RNA or DNA)
Enzymes (not always)
Biomembrane (lipids from host cell)
Enveloped proteins (from the virus)
What’s a complex virus?
Protein coat (capsid)
Nucleic acid (RNA or DNA)
Enzymes (not always)
Complex protein tail
3 distinct ways viruses enter the host cell?
Endocytosis - enters as a Trojan horse
Membrane fusion
Injection - inject genetic information and leave rest of virus particle behind
Lifecycle of a complex virus?
Virus attaches to surface receptors
The tail contracts, enzymes break the cell wall, and the core needle pinches the cell
The content of the head (proteins, DNA/RNA) is released into the cell
The bacterial metabolism is disrupted and the genomic DNA degraded
Viral DNA is transcribed into mRNA
Viral DNA is replicated
mRNA is translated into viral proteins
Complex virus particle self assembles (50-100)
Cell lysis and release
Lifecycle of an enveloped virus
Entry into the host cell by endocytosis or membrane fusion
Release of DNA into cytoplasm, motors (dynein) can also bind directly to the viral capsid so virus is making use of the intracellular transport machinery
DNA made and translation of proteins occurs, new viruses made
Budding occurs, virus leaves cell taking membrane to form it’s envelope
What are magnetotatics?
Bacteria that navigate along magnetic fields by detecting it
They contain crystals of an iron material called magnetosomes, they use them for magnetotaxis (a compass)
Gram negative
Main actin like proteins in prokaryotes?
MreB - cell shape
ParM - DNA partitioning
MamK- forms filaments
Modes of motility of bacteria and archaea and how they move ?
Swimming
Swarming - on surfaces
Gliding
Twitching
Flagella rotating due to protons generating ATP
Have directly motility for food
Pili retract and grow to allow twitching (creates colonies) or slow gliding
How do bacteria enter mammalian cells?
They force the host cell to take them up
A protein ring assembles into a needle
The needle injects proteins into the human cost cell to manipulate the actin cytoskeleton, thereby forcing uptake
Type 3 or type 6 secretion systems inject the proteins
2 major growth forms of fungi?
Yeast:
Uniceullar and often rounded
Grow by budding
Hyphal:
Usually multi-cellular and elongated
Extend by polarized growth
What does fungal growth rely on?
Delivery of vesicles to the growth region (bud or hyphal tip) via the cytoskeleton and the fungal motors on them
Dynein to negative end, kinesis to positive end
What’s the spitzenkorper?
The apical body involved in hyphal growth
It’s a vesicle cluster at the tip, it serves as a vesicle supply centre
Contains secretory and recycling vesicles
Hyphal growth relies on this structure
Describe hyphal growth?
Transport along the cytoskeleton
Storage of vesicles in the spitzenkorper
Release and fusion with plasma membrane
Function of Woronin bodies?
Prevent if one cell dies in fungal chain the cytoplasm leaking out of all of them
Blocks the gaps between the cell bodies by plugging
They are specialised peroxisomes
Contain hexagonal crystals of the protein Hex1
Why do mushrooms release spores?
For reproduction
What actually is a mushroom?
The organisation of basidiomycete fruiting body
Mechanism of spore discharge in basidiomycetes?
Two water drop are formed Due to secretion of secretion of mannitol and other hygroscopic sugars
on the surface of the spore
The Adaxial drop and the Buller’s drop
Buller’s drop increases in size due to recruitment of atmospheric water
Sudden change of centre of gravity
by fusion of both drops create a propulsive force
How do ascomycetes release spores?
Turgur pressure built up within the ascus and a sudden burst
What are chloroplasts?
Use light, carbon dioxide, and water to produce glucose and oxygen = photosynthesis
Surrounded by a double membrane
Have inner membrane system
Have their own genome
What’s the thylakoid?
membrane compartment; the thylakoid membrane surrounds the thylakoid lumen
What’s a granum?
A stack of thylakoids
Contains light capturing system and ATP synthase
What’s the storm?
Matrix of the chloroplast
Contains fixation enzymes, chloroplast DNA, Ribosomes
Why are plants green?
Doesn’t absorb green light
So they don’t use the visible spectrum very efficiently
But if they did (say there were black) too much heat would be generated
Mainly absorbs blue and red light.
Why do leaves turn from green to yellow to red in autumn?
Sense of reduced photosynthesis
Degradation and recycling of cellular components is induced
Chloroplasts turn into gerontoplasts
Breakdown products get stored in the plant vacuole
Formation of anthocyanin that protect against too much light and oxidative stress (turns them red)
Finally the cells get killed and the recycled cellular components released from the vacuole and delivered to the plant
Are chloroplasts motile? Why?
yes
To avoid photo damage from light
3 steps:
Photoperception - Plant blue - light photoreceptors perceive the light
Signal transduction - Calcium signalling
Chloroplast movement - Motor dependent
What is cytoplasmic streaming?
Occurs independently of chloroplast movement
Depends on energy and requires F-actin
There is a nonmoving cytoplasm (Exoplasm) and a streaming cytoplasm around the vacuole (endoplasm) it’s moving due to sliding theory (so basically just motors moving everything which drags the cytoplasm)
Features of plant cell wall?
Primary wall is flexible and unorganised,
The secondary wall is formed in fully developed cells far more rigid. Contains Lignin (wood)
Both contain cellulose
Cellulose synthase complex forms a rosette in the plant plasma membrane in which a nascent 36 gluten chains are extruded into the wall. These organise the walls
What control expansion of the cell?
Plant vacuole
Generates outward pressure (turgor) that is counter balanced by the cell wall
Variation in cell wall rigidity due to orientation of the cellulose fibres directs cell expansion
What is plasmolysis?
The reversible shrinkage of the plant cell, due to reduced turgor pressure in the vacuole
Reveals cell-cell contacts
What connects plant cells?
Cytoplasmic bridges called plasmodesmata
They allow free passage of small molecules
Can be plugged by formation of callose if one cell is infected
How do plant cells divide?
Microtubules form a plant-specific array called the phragmoplast in the middle
Vesicles then transported to here to form the cell plate by fusing
Endoplasmic reticulum crosses the cell plate (helps form plasmodesmata)
Cell wall in interior fuses with plasma membrane
What is cellular endosymbiosis?
Is when a single cell organism lives in a host cell
What is endosymbiosis theory?
Three fundamental organelles, mitochondria, chloroplasts and basal bodies of flagella were once themselves free-living cells
With the mechanisms of:
Phagocytosis of a prokaryote
Host cell and endosymbiont reproduce
Development of an interdependence
Arguments for endosymbiosis theory?
Mitochondria and Chloroplasts have their own circular genomes
Mitochondria and Chloroplasts have 70S ribosomes which is the same as prokaryotes
Chloroplasts and cyanobacteria (prokaryote) ave thylakoid membranes
Chloroplasts and mitochondria both have a double membrane - derived from incomplete phagocytosis
