Concept 5+6 Flashcards
(101 cards)
1
Q
What does the cytoplasm consist of? 2
A
1) Cytosol
- jelly fluid, mostly made out of water
2) Cytoskeleton
- system that uses 3 diff types of filaments that all work together
- 1) microtubules 2) microfilaments 3) intermediate filaments
2
Q
Function of the cytosol 4
A
WHAT PROCESSES OCCUR HERE?
1) Site of numerous reactions
2) INTERMEDIATES of reactions are shuttled around here
WHAT DOES IT HOLD?
3) Has many raw materials essential for macromolecule production
4) Holds organelles
3
Q
Cytosol vs cytoplasm 3 differences
A
CYTOSOL
1) Liquid part of the cytoplasm
2) Excludes the organelles - Made up of water, ions, CYTOSKELETON
3) Doesn’t show movement - less dynamic
CYTOPLASM
1) Gel-like substance
2) Contains organelles BUT no nucleus
3) Shows movement - cytoplasmic streaming
4
Q
Cytoskeleton - smallest to biggest
A
Microfilament -> intermediate filament -> microtubule
TIP
- filament = wire
- intermediate = middle
- tube = big!
5
Q
Cytoskeleton - the 3 types - STORY SHAPE
A
MICROTUBULES
- Hollow tubes - pearl necklace wrapped around a finger
MICROFILAMENTS
- 2 pearl necklaces - wrapped around like a braid
- so…DOUBLE HELIX
INTERMEDIATE FILAMENTS
- rope
- fibrous proteins - diff for diff cells
6
Q
Cytoskeleton - the 3 types - made up of what?
A
MICROFILAMENTS
- ACTIN strand, double helix x2
= 1 pearl necklace
INTERMEDIATE FILAMENTS
- FIBROUS proteins
eg. keratin - diff for diff cells
- fibrous proteins are super coiled into these thick cables
MICROTUBULES
- TUBULIN DIMER
(2 units) 2 pearls
- Made up of 13x tubulin strands
7
Q
Microtubules, microfilaments, intermediate filaments - common function 2
A
1) Maintain STRUCURE
2) Maintain CELL SHAPE
- Microfilament + intermediate filament = TENSION BEARING (resist PULLING forces)
- Microtubule = GIRDERS (resist PUSHING/COMPRESSING forces)
8
Q
Microtubules - function 3
A
BIGGEST
- SO ARE ABLE TO MOVE THINGS AROUND!!!
1) OUTSIDE - Form cillia + flagella
- tail/hair, allow for cell to swim
2) INSIDE - Move organelles
3) ORGANELLE - Mitosis
- help move chromosomes
9
Q
Microfilaments - function 4
A
PEARL NECKLACE BRAIDED TOGETHER
VERY FLEXIBLE:
1) Help cells change shape
2) Cytoplasmic streaming
- cytoplasm moves from one area to another
- helps with movement
LIKE A LINE:
4) Cell division - cytokineses
- forms the CLEAVAGE FURROW
- splits the cell into 2 daughter cells
ACTIN:
3) Role in muscle contraction
10
Q
Cytokinesis/cell division differences in plants vs prok vs animals
A
ANIMALS
- microfilament, actin
- pinching of membrane
- forms contractile ring -> cleavage furrow
PLANTS
- vescicles fuse to form a cell plate
PROKARYOTES
- FTSZ protein, cell wall produced
11
Q
Intermediate filaments - function 2
A
STRONG ROPE - HOLDS THINGS INTO PLACE
1) ANCHOR the nucleus + other organelles
- SCAFFOLD
- holds them in place!
2) Form nuclear lamina
- this is a mesh supporting the nucleus’s shape
12
Q
Endomembrane system 3
A
1) Endoplasmic reticulum ER (RER+SER)
(attached to the nuclear envelope)
2) Golgi apparatus
(cytoplasm)
3) Secretory vesicles vs lysosomes
(come out of the golgi apparatus)
13
Q
Endoplasmic reticulum ER - 2 types, structure
A
STRUCTURE:
- Connected to the nuclear envelope
- Made up of CISTERNAE = flattened, sac-like membrane structures
- High SA:Vol ratio
- Can changes in structure -> therefore function
2 TYPES:
1) SMOOTH ER
- Lacks ribosomes
2) ROUGH ER
- Studded with ribosomes
14
Q
ER function
A
BOTH
- Provides SURFACES for the synthesis of proteins, lipids AND glycoproteins, carbohydrates
(Glycoproteins = proteins w/ sugar attached, typically oligosaccharides)
SMOOTH
- Makes the most lipids
ROUGH
- Makes lipids + proteins
15
Q
ER definition
A
Production and assembly of complex carbohydrates like oligosaccharides and polysaccharides, proteins, lipids, glycoproteins
16
Q
Golgi apparatus - structure
A
SAME AS ER…
- Made up of CISTERNAE/GOLGI STACKS = flattened, sac-like membrane structures
- Altogether golgi stacks = golgi apparatus
BUT…
- Exist in the cytoplasm
- POLAR (front + back ends)
Front = cis face
Back = trans face
17
Q
Golgi apparatus - definition
A
collection, packaging, and distribution of molecules synthesized in the ER.
18
Q
Secretory vesicles
A
- DOESN’T STAY IN THE CELL
- Transports molecules (eg. hormones, digestive enzymes) out of the cell via EXOCYTOSIS
19
Q
Lysosomes - structure, conditions
A
- Vesicles, REMAINS IN THE CELL
- Membrane bound
- Contains hydrolytic enzymes
-> come from the RER + Golgi
SO…
- Internal pH is acidic, 4.5
- Optimal for enzymes
20
Q
Lysosomes - function 2
A
- ENZYMES BREAK DOWN THINGS
- BY FUSING WITH ANOTHER VESICLE
1) DIGESTION OF MATERIALS TAKEN IN BY ENDOCYTOSIS
- Via endocytosis, there will be a food vacuole (ie. vesicle) containing food coming INTO the cell
- Lysosome will fuse with the food vacuole
- Hydrolytic enzymes will digest + break down the food particles
2) AUTOPHAGY - RECYCLING OF OLD ORGANELLES
- Vescicle inside the cell will contain damaged organelles
- Lysosome will fuse with this vesicle
- Hydrolytic enzymes will digest + break down the organelle components
21
Q
Lysosomes - animal vs plant
A
- Lysosomes only found in ANIMALS
- EXACT Lysosome version in plants is the VACUOLE
- Lysosome SIMILAR version in plants are MICROBODIES
22
Q
Microbodies, lysosome, vacuole - 3 key differences, 1 similarity
A
LYSOSOME
1) Hydrolytic enzymes
2) Enzymes come from the RER
3) Internal acidic pH
MICROBODIES
1) Oxidative enzymes
2) Enzymes do not come from the RER
3) Internal neutral pH
VACUOLE
1) Hydrolytic enzymes
2) Enzymes come from the RER
3) Internal acidic pH
SIMILARITY = all membrane bound
23
Q
Whole process of the endomembrane system 4
A
ENDOPLASMIC RETICULUM
1) The RER and SER make proteins, lipids, carbohydrates, glycoproteins
2) These are packaged into vesicles
GOLGI APPARATUS
3) Vesicles arrive at the Cis face, -> travel thorugh the Golgi -> leave at the trans face
- Inside the golgi…
- Proteins are biochemically modified
- Sugars can be trimmed or added to glycoproteins
- Polysaccharides made here
- Final products are packaged into NEW vesicles, transported out the trans face
VESICLES
4) These vescicles can either be lysosomes OR secretory vesicles
- one stays in the cell, other leaves
24
Q
Endomembrane system - definition, what it consists of
A
DEFINITION = system of compartments, made up of membrane bound components of the cell that make, package, ship proteins + molecules
Components:
- Nuclear envelope
- Endoplasmic reticulum (ER)
- Golgi apparatus
- Lysosomes / Vacuoles (in plants)
- Vesicles
WHY?
- they are part of the system as they all continue the other organelle’s duty, follow one linear process
- eg. later microbodies won’t be involved as the golgi doesn’t produce this vesicle
25
How did the endomembrane system form?
- INVAGINATION of the plasma membrane around nucleoid of a prokaryote cell
- Forms nuclear envelope
BUT...
- Invaginations with RIBOSOMES led to the formation of ER + eventually the whole endomembrane system
26
Lysosomes don't exist in plants - what do plants replace this with? structure, function
VACUOLES
- Single membrane = tonoplast
SIMILARITIES IN STRUCTURE
- Also contain hydrolytic enzymes
FUNCTION
- Other than breaking down products...
- Store nutrients, pigments
- Main cell pressure (turgidity)
27
Microbodies - general function 3
SAME JOB AS LYSOSOME - BREAKING DOWN MOLECULES/BROKEN ORGANELLES
DIFFERENCES:
- Contains enzymes that DO NOT come from the RER's ribosomes
- Neutral internal pH
- Contain oxidative enzymes
28
Microbodies - 2 types
1) Peroxisomes
- break down amino acids
2) Glyoxysomes
- break down fatty acids
29
Phospholipids - structure
(generic - detailed)
GENERIC:
1) Hydrophilic head
2) 2x Hydrophobic tail
DETAILED: WHY??
1) CHARGED POLAR HEAD
- Choline has a positive charge
- Phosphate has a negative charge
- Phosphate group = highly polar, lots of oxygen atoms
-> we don't look at overall charge, but individual charges that can result in attractions w/ water
- SO...form electrostatic/dipole interactions
2) NON-POLAR FATTY ACID CHAINS
- Nonpolar, won't be attracted to water
- SO...form dispersion forces
30
Why is the membrane = fluid mosaic model
FLUID
- Phospholipids + proteins can move side to side via DIFFUSION
- Particles, ions, molecules can move through the membrane
MOSAIC
- Scattered pattern of cholesterol, carbos, phospholipids etc.
31
Why is the membrane being fluid important? 2
1) Allows entry + exit of substances through the membrane
2) Transport proteins can move to align with molecules
- eg. ion channels move to where ions are
3) Endocytosis
- Membrane must bend to form vesicles
32
Are membranes always enclosed?
Membranes in biological systems are enclosed and never open-ended unless damaged.
33
space inside a membrane
cisterna or vesicle.
34
Why does a phospholipid bilayer form?
- Heads outside, tails inside
- Because there are 2 aqueous environments
1) Extracellular space (outside of the cell)
2) Cytoplasm
HENCE ONE BILAYER = ONE MEMBRANE!!
35
Cholesterol importance in membranes/ phospholipid bilayer?
STRUCTURE
- polar head
- large non-polar body (4 ring structure)
WHERE DOES IT BELONG IN THE MEMBRANE?
- Head WITHIN/AMONG the phospholipid heads
- Tails amongst the other tails
FUNCTION
-REDUCES fluidity of the membrane
- Nonpolar forms dispersion forces w/ fatty acid chains
- Hence fatty acid chains pack more closely - PULLS THEM TGTH
36
Transmembrane proteins - why is there no gaps between this and the phospholipids in the membrane?
- Alpha helix some NON-POLAR R groups sticking out
- Creates dispersion forces w/ fatty acid tails
- Attraction keeps them packed close tgth
37
Identify structures in the bilayer membrane - GDOCS
YELLOW THINGS INSIDE THE MEMBRANE
= cholesterol
BLUE ROPES INSIDE THE CELL
= alpha helix, double strand
= microfilaments
PINK STRUCTURES
= transmembrane proteins (ie. within the membrane)
Y SHAPE
= carbohydrates
= receptors for cell signalling
BEIGE ROPES ON TOP
= cillia
38
Is the phospholipid bilayer fully permeable?
NO. SELECTIVELY PERMEABLE
WHAT CAN PASS:
- Nonpolar/uncharged molecules
- Small enough to pass through polar heads
- Can pass through the nonpolar tails to the other side
WHAT CAN'T PASS:
- Polar/charged molecules
- Cannot pass through the nonpolar tails -> SO...need a TRANSPORT protein!
39
Saturated vs unsaturated fatty acids - which will create a more fluid membrane?
UNSATURATED
- Double bonds exist -> not the maximum number of H bonded
- Double bonds create KINKS (ie. bends in the carbon chain)
- This PREVENTS CLOSE PACKING
- Therefore UNSATURATED = MORE FLUID
Unsaturated = double bond = kink = tails do not pack so closely together
SATURATED
- All single bonds --> maximum number of H bonded
- Single bonds create a STRAIGHT carbon chain
- This CAUSES CLOSE PACKING
- Therefore SATURATED = LESS FLUID
40
Long vs short fatty acid tail - which will create a more fluid membrane?
LONGER
- higher DISPERSION force between each other
- pack more CLOSELY TOGETHER
- less fluid
41
How does increasing temp increase permeability of the membrane?
- adds kinetic energy - causes vibration of phospholipids
- this will DISRUPT the DISPERSION FORCES holding the phospholipids tgth
- therefore membrane will break apart, more permeable
42
Chemical composition vs key features of a cell membrane
- CHEMICAL COMPOSITION = what the membrane is MADE OUT OF
- KEY FEATURES = GENERAL FUNCTION
43
Key features of a membrane
1) Selectively permeable membrane - controls what enters and exits the cell
2) Important in homeostasis - compartmentalisation
3) Communication with adjacent cells + receive signals
4) Structural role, sometimes affects cell shape
44
Chemical composition of a cell membrane + why its called fluid mosaic model
- PHOSPHOLIPID BILAYER
- Consists of phospholipids, cholesterol, carrier + channel proteins
NO NEED TO MENTION PROPERTIES, FUNCTION OF THESE!!
- Mosaic = PROTEINS are irregularly arranged in the bilayer
- Fluid = cholesterol can move laterally within the membrane
45
3 types of transport in the membrane?
1) Diffusion
- High conc to low conc
- Eventually reach DYNAMIC EQUILIBRIUM (solute will still move, but conc remains the same on either side)
2) Osmosis
- Movement of water from an area of high water potential to low water potential
- To resist osmosis, stop change in volume
3) Facilitated diffusion
- Transport of hydrophillic molecules through the membrane
- Using a TRANSPORT PROTEIN (channel, carrier)
4) Active transport
- Transport of substances against a conc gradient (low to high concentration)
- Using a CARRIER PROTEIN
46
2 types of transport proteins
1) Channel proteins
- Ions and hydrophillic substances can pass right through
2) Carrier proteins
- Molecules bind to this
- As molecules bind, they change shape to move the molecules to the inside of the cell
47
Aquaporins
a CHANNEL PROTEIN specifically for water
48
Exchange pump
- active transport (Na+, K+)
- a CARRIER PROTEIN that moves one solute in one direction and another in the opposite direction.
49
Factors Affecting Active Transport (4)
RMB THAT THIS USES A CARRIER PROTEIN!!
1) Availability of the carrier protein.
2) Involvement in transport of other substances.
3) Substrate concentration.
4) ATP availability (for activation).
50
Osmosis and Red Blood Cells
- hypotonic, isotonic, hypertonic
HYPOTONIC:
- Lower solute concentration outside the cell -> higher water potential
- Water flows into the cell.
- Cell ruptures (LYSIS).
ISOTONIC
- Same solute concentration on both sides.
- Water flows in and out freely.
- Cell is normal
HYPERTONIC
- Higher solute concentration outside the cell -> lower water potential
- Water flows out of the cell.
- Cell shrivels
51
Osmosis in Plant Cells
- hypotonic, isotonic, hypertonic
HYPOTONIC:
- Lower solute concentration outside the cell -> higher water potential
- Water flows into the cell.
- VACUOLE fills, cell becomes TURGID
ISOTONIC
- Same solute concentration on both sides.
- Water flows in and out freely.
- Cell is normal - FLACCID
HYPERTONIC
- Higher solute concentration outside the cell -> lower water potential
- Water flows out of the cell.
- Cell becomes PLASMOLYZED
52
3 types of endocytosis
1) Receptor mediated endocytosis 🎯
= Target molecule binds to receptor protein on the cell membrane
- This triggers the formation of a vesicle around the target molecule
2) Pinocytosis 🥤
= Cell drinking
- Membrane SINKS inwards
- Extracellular fluid w/ dissolved nutrients enters the gap, vesicle forms around it
- Vesicle enters the cell
3) Phagocytosis 🍔
= Cell eating
- Membrane SINKS inwards
- Solid particles/cells/bacteria/pathogens enters the gap, vesicle forms around it
- Vesicle enters the cell
(bacteria in this case would be broken down by a lysosome)
53
Exoxytosis
EJECTION of material outside of a cell
- Intracellular vesicles fuse with the membrane
- Contents released into the extracellular space
54
Speed of Receptor-Mediated Endocytosis
1) The number of receptors on the membrane
2) The concentration of the target molecules
55
Sodium-Potassium Pump 3
THIS IS ON A CARRIER PROTEIN!!
1) 3 Sodium ions in the cytoplasm binds to the sodium pump.
2) Na+ binding stimulates the pump to be phosphorylated (add a phosphate) - BY ATP
3) Carrier protein changes shape. New shape means 3Na+ LEAVE the cell, 2K+ ENTERS the cell
- molecule binding will cause a change in shape of the carrier protein
- BUT this change in shape needs ATP.
Carrier protein has an ATP binding site. Protein will hydrolyse it into ADP so that energy can be released. This energy will be used to change shape
56
Cell division is fundamental for? 2
CELL DIVISION = one cell turns into 2, genetically identical
1) Growth + repair
2) Reproduction
57
Is the rate of cell division same among organisms?
NO
Varies greatly based on organism's needs + function
Plants: Quick division during germination.
Microbes (e.g., E. coli): Rapid division, forming colonies overnight.
Animal embryos: Rapid division (e.g., human fertilized egg to organism in 40 weeks).
Certain cells (e.g., neurons): Do not divide and are not repaired.
58
Genome definition - compare in prok vs euk
Genome: The complete set of DNA in a cell. (ALL DNA IN A CELL)
Prokaryotic genomes: Typically have one DNA molecule.
Eukaryotic genomes: Have many DNA molecules
59
Euk vs prokaryotes type of DNA
Eukaryotes
- linear DNA -> chromosomes
Prokaryotes
- plasmids
- circular DNA -> STILL chromosomes, but different
- held in nucleoid
60
For successful cell division 2
1) Genetic material must be copied accurately.
2) Each daughter cell must receive an identical copy of the genome.
61
DNA replication vs mitosis
- DNA replication: The duplication of genetic material
- Mitosis: Nuclear CELL division in eukaryotes - Production of a genetically identical cell
62
Cell division - prokaryotes + eukaryotes
ALWAYS 2 KEY PHASES
EUKARYOTES
1) Interphase:
- G1 phase, S phase, G2 phase
- Not undergoing division.
2) Mitosis: The division phase.
PROKARYOTES
1) "Interphase":
- B phase = gap phase
- C phase = replication phase
2)
- D phase = Binary fission
63
Interphase in eukaryotes 3
3 KEY PHASES:
1) G1 Phase (First Gap Phase):
- Cell grows in preparation for division.
- Restriction points = Cells decide whether to continue dividing or exit the cycle - crucial for preventing uncontrolled division (cancer)
2) S Phase (Synthesis Phase):
- DNA replication occurs.
3) G2 Phase (Second Gap Phase):
- Further increase in cell size.
- Checking for errors in DNA replication.
64
Earliest stage in prokaryotes in cell division 3
1) B = Gap phase:
- No division occurs (similar to interphase in eukaryotic cells).
- This phase is skipped in rapidly dividing cells.
2) C = Replication
- The single DNA molecule is replicated in the nucleoid.
65
Initiation in prok vs euk
PROKARYOTES
- Inactive DNA-A becomes active through ATP
- Binds to binding boxes
- Triggers DNAB (helicase)
EUKARYOTES
- ORC
- Binds to origin of replication
- Triggers helicase
66
Eukaryotic DNA replication - what are we working on? Initation?
WHAT ARE WE WORKING ON?
- Multiple ORIGIN OF REPLICATION
INITIATION:
- Origin Recognition Complex (ORCs), binds to the origin of replication
TRIGGERS HELICASE TO WORK
67
Eukaryotic DNA replication 4
1) Helicase to unzip the DNA
-> So... Forms a REPLICATION BUBBLE with 2 REPLICATION FORKS
2) ONCE DONE...We are left with a leading strand + lagging strand
-> depends on direction of unzipping
-> DNA polymerase works in the 5’ to 3’ DIRECTION
- Leading strand is synthesised CONTINUOUSLY
- Lagging strand is done DISCONTINUOUSLY
3) On the lagging strand...
- DNA primase will lay primers
- Dna polymerase will bind, synthesise DNA
- DNA fragments in between primers = OKAZAKI FRAGMENTS
4) Afterwards...
- RNase H removes primers
- DNA polymerase fills up the gaps
- BUT this will leave NICKS - gaps in dna
- Joined together by DNA ligase
68
extra eukaryotic dna replication - ignore
11)ALL DONE... BUT
- on the REPLICATED LAGGING dna strand, the last primer removed at the end creates an overhanging TEMPLATE/OG DNA
12) Telomerase extends the overhanging TEMPLATE/OGstretch with non coding DNA
- primase binds, dna polymerase binds, replicated DNA strand made
- This prevents the loss of coding DNA in later replication cycles
13) Replication finishes by having replication bubbles merging together
69
What is a problem that can occur as DNA is unzipped during DNA replication? How is this resolved? - for prokaryotes AND eukaryotes (2 problems)
1) GET TANGLED
- Form "hairpin loops"
2) CLOSE BACK UP
- the 2 strands of DNA come back together
SOLUTION
= Single strand binding proteins (SSB) binds to each single stranded DNA
70
Prokaryote DNA replication process - WHERE IS IT DONE, WHAT STARTS IT? INITIATION (4)
WHERE IS IT DONE?
- In prokaryotes there is ONE OriC (Origin of Replication)
INITIATION:
1) Initiation factor DNA A
- BUT only becomes active when ATP binds to it
2) This ALLOWS active DNA A will bind to binding boxes
(Boxes are 9 base pairs upstream of OriC)
3) This will cause the DNA at the OriC region to UNZIP A BIT
(at every 13 base pairs
- These separation points create loops (bubbles) along the DNA structure)
4) DNAB (a helicase enzyme) will FULLY UNZIP the DNA
- DNAB's job is to FULLY OPEN up these DNA loops.
- This opening process is called "melting" the DNA.
///IGNORE?
6) Now that the DNA is open, DNA polymerase can start copying it.
- As DNA polymerase works, it changes DNA A-ATP to DNA A-ADP
- This provides energy for replication
It also reduces active DNA A
-> Ensures new replication doesn’t happen before current replication is complete
71
Prokaryote DNA replication process - difference to eukaryote 2
NO DIFFERENCE EXCEPT...
1) Initiation
- Euk = ORC (origin recognition complex)
- Prok = active DNA-A
2) Completion
- Replication is finished when 2 replication forks will meet at the TERMINATION SITE
- As dna is circular
72
What happens when dna replication occurs on a prokaryotic circular dna?
- Dna ahead of the fork becomes overwound + supercoiled - creates a TORSINAL STRAIN
- Type 1 topoisomerase creates a nick, pulls
another strand to pass through, then ligates the dna molecule back
73
Binary fission - definition
- method of asexual reproduction
- cell splits into two, resulting in two identical daughter cells.
74
Binary fission - process
START WITH REPLICATION
1) Replication starts at the origin of replication (OriC)
2) Replication finishes
- One copy of the origin moves toward the end of the cell. (through ACTIN)
FORMING 2 CELLS, EACH WITH ONE COPY OF OriC
3) Cell Elongation:
- The cell elongates, preparing for division.
4) Membrane Pinching:
- The plasma membrane pinches inward through FTSZ Protein
(SO NOT SAME AS EUKARYOTIC CYTOKINESIS AT ALL!!)
5) Cell Wall Deposition:
- This forms a new cell wall!
FINAL PRODUCT
6) Daughter Cells Formation:
- Two daughter cells are formed
- identical chromosome coiled into a nucleoid.
75
FTSZ protein - what is it similar to, function 2
- Filament temperature-sensitive protein FOUND IN PROKARYOTES
SIMILAR TO
- TUBULIN!!
- it is ACTIN in eukaryotes
FTSZ Function
1) Will form a - RING OF PROTEIN FIBRES WILL CONSTRICT THE CELL
2) Involved in division of chloroplasts and mitochondria
76
# Stages, summary of each stage
Mitosis stages
1) INTERPHASE
2) MITOSIS: 5 stages
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
(PPMAT)
3) CYTOKINESIS
1) PROPHASE
**getting ready to board a flight
- chromatin condenses into chromosomes.
-> These are made up of sister chromatid pairs joined at the centromere
- centrosomes (L-shaped organelles) start migrating to opposite sides of the cell.
- SPINDLE FIBRES BEGIN to extend from each centrosome (microtubules)
2) Prometaphase:
** starting to feel real!
- The nuclear envelope dissolves
- Kinetochores form on both sides of the centromeres, one for each chromatid
- Spindle fibres attach to the kinetochores
3) METAPHASE
LITERALLY - MIDDLE
- The spindle apparatus organizes the chromosomes to line up with the cell's equator
4) ANAPHASE
LITERALLY - AWAY
- Spindle fibres shorten, separating the sister chromatids.
- Now separate, each chromatid is referred to as a chromosome.
5) Telophase
- The spindle apparatus disassembles.
- 2 nuclear envelopes form around genetic material which has loosened
// Cytokinesis:
- Happens at the SAME TIME as telophase.
- The cell is divided to form 2 cells that are genetically identical
77
Cytokinesis in Animal vs. Plant Cells
ANIMAL
- in the middle of the elongated cell / 2 nuclei
- A CONTRACTILE RING forms + separates the cytoplasm
PLANT
- Vesicles fuse to form a CELL PLATE between the daughter cells
- will eventually becomes the cell wall.
SUMMARISED
- Animal = contractile ring
- Plant = vesicles fuse -> cell plate -> cell wall
78
Contractile ring vs cleavage furrow
The contractile ring causes the cleavage furrow by contracting and pulling the membrane inward.
The furrow is the visible consequence of ring activity, not the active machinery itself
79
Cilia vs pilli
CILIA = movement in eukaryotes
PILLI = movement in prokaryotes
80
will prokaryotes or eukaryotes divide a bit when conditions are unfavourable? which will just not divide at all?
- Prokaryotes will typically not divide at all when conditions are unfavorable. They tend to enter a dormant state and wait for better conditions.
-> eg. FOOD
- Eukaryotes, even under unfavorable conditions, have some cells continue dividing
WHY?
- eukaryotes more complex
- some specialised cells may need to still continue to keep on functioning
81
Contractile ring vs cell plate
RING
- made up of actin microfilaments + myosin
CELL PLATE
- made up of golgi vesicles - fused to form a cell plate
82
Difference between DNA replication in prok and euk cells?
1) Origin of replication
- Prok only have one origin
- Euk have more than 1- replication starts at numerous regions
2) No. of chromosomes
- Pro has 1 circular chromosome
- Euk has more than 1 chromosome
3) DNA replication + separation of daughter chromosomes into opposite sides of the cells (segregation)
- Prok occurs right after another, or simultaneously
- Euk separated - totally diff parts of the cell cycle, never overlap
WHY DIFFERENT?
- Separation of DNA is more complicated in eukaryotes
- This ensures less chance of errors in DNA
83
Cell division signals
- these TRIGGER cell division
eg. fructose as reproductive signal
- if fructose conc drops - cell division SLOWS SOWN
- if fructose conc increases - cell division will occur RAPIDLY
** NOT STOP/START - just faster or slower
84
What is there at every stage in mitosis?
RESTRICTION POINTS!!!
- RED LINES = restriction points, 4x total
- makes sure everything is perfect w/ the cell before proceeding to next part of the cell cycle
- OR ELSE CANCER!!
- Check for errors, DNA damage
- At each point cyclin may or may not be produced, but CDK will always be present
85
Cells that do not divide + NOT DOING ANYTHING - what phase they in?
- Cells arrest in G0 phase
86
interphase, PMAT - what regulates this process? 2
1) CDK
- always present
- cyclin dependent kinase
2) Cyclin
- only made at CERTAIN times WHEN IT IS NEEDED
- 4 types, one for each stage of PMAT
- When this binds to CDK, it will ALLOW THE CELL CYCLE TO CONTINUE (NO LONGER BLOCKED)
87
interphase + PMAT - when must this process be regulated? - external factors 3
- Not enough energy/resources/free ATP in the cell
- Not enough organelles to divide
- Cell too small to divide (must have a certain volume)
88
cell cycle checkpoints - DEFINITION
signaling pathways that regulate the cell cycle’s progress (ie. make it pause)
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cell cycle checkpoints + cyclin+CDK
- there are many CELL CYCLE PHASES (g1,g1/s,s,m etc.)
- there are always CHECKPOINTS at each phase
- BUT only specific things will TRIGGER these checkpoints (ie. for the pathways to start)
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What triggers will cause the cell cycle to pause at each checkpoint?
G1
- Checkpoint trigger = DNA damage, when the cell is too small
S
- Checkpoint trigger = Incomplete replication, dna damage
G2
- Checkpoint trigger = DNA damage
M
- Checkpoint trigger = Chromosome unattached to the spindle
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Why might a cell be too small for cell division?
not enough resources, stressful environment
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CDK - HOW DOES IT REGULATE THE CELL CYCLE? - GENERAL STEPS
1) CDK IS ALWAYS PRESENT
- 2 binding sites
2) CYCLIN BINDS TO CDK ON ITS ALLOSTERIC SITE
3) TWO THINGS BIND TO CDK
- ATP + target substrate
4) WHAT HAPPENS TO TARGET MOLECULE?
- Phosphate is a negative charge
- Target molecule change in shape AND function!!!
- Substrate turned OFF OR ON
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CDK - HOW DOES IT REGULATE THE CELL CYCLE? - GENERAL STEPS EXPLAINED
1) CDK IS ALWAYS PRESENT
- Cyclin dependent = needs cyclin
- Kinase = enzyme that adds phosphates (phosphorylation)
- Imagination = 2 binding sites -> one on top (allosteric), one at the bottom (active)
2) CYCLIN BINDS TO CDK ON ITS ALLOSTERIC SITE
- Active site of CDK is now open (exposed)
3) TWO THINGS BIND TO CDK
- ATP + target substrate binds to CDK
- ATP phosphorylates the target molecule
4) WHAT HAPPENS TO TARGET MOLECULE?
- Phosphate is a negative charge
- Target molecule will have a change in tertiary structure
- SO...Change in shape AND function!!!
- SO...phosphate will either turn it OFF OR ON
- If it's function can occur, we say it is ACTIVATED
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CDK - HOW DOES IT REGULATE TRANSITION FROM G1 TO S PHASE? 4
1) CDK IS ALWAYS PRESENT
- 2 binding sites
2) CYCLIN BINDS TO CDK ON ITS ALLOSTERIC SITE
- Specifically G1/S cyclin!!
- Change in active site shape
3) TWO THINGS BIND TO CDK
- ATP + target substrate
- Target substrate is RB!!
- Phosphate is added to RB
4) WHAT HAPPENS TO TARGET MOLECULE?
- RB = bouncer at a night club --> function is to STOP cell going from G1 to S phase!!
- So normally it is ACTIVATED
- RB ALONE = stops cell cycle = so its ACTIVE
- RB WITH PHOSPHATE
ADDED = "given money" = it doesn't block the cell cycle = so its INACTIVATED by phosphate
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CDK - WHAT HAPPENS IF DNA IS DAMAGED IN G1?
DON'T WANT CYCLIN TO BIND, AS THIS ALLOWS THE CELL CYCLE TO CONTINUE
SO...
- p21 protein will act as a COMPETITIVE INHIBITOR
- p21 will bind to the allosteric site of the CDK
- therefore cyclin can't bind
- cell cycle will PAUSE while DNA is being repaired
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Types of cyclin, how many?
FOUR
1) G1 cyclin
2) G1/S cyclin
3) S cyclin
4) M cyclin
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When one stage of the cell cycle is fininshed eg. finished with G1, now moving onto S, what occurs?
We want to make sure that process STOPS - doesn't occur simultaneously!
- G1/S cyclin BREAKS DOWN
- CDK has a change in active site shape
- therefore RB can't bind, won't be inactivated
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Is cyclin and CDK the only way of regulating the cell cycle?
NO!!
1) External signals
- eg. hormones
- can start/stop the cell cycle
2) Growth factors
- proteins that STIMULATE the cell cycle
- eg. proteins inside platelets, released when skin is cut, stimulates growth + cell division of skin cells
- eg. interleukins are growth factors stimulate growth of blood cells
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Growth factors - HOW do they STIMULATE the cell cycle
- activate signal transduction pathways that end with cyclin synthesis (CYCLIN WILL LET CELL CYCLE CONTINUE!!)
- the cyclin will activate CDK and so forth
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If a mutation makes cyclin-CDK complexes more likely to phosphorylate RB, the result will be ___ active RB molecules and ___ cells going through the checkpoint
- RB function = stop cell cycle like a bouncer
- so normally it is ACTIVATED (as cell cycle doesn't occur all the time!)
-if phosphorylated, it will allow cell to pass through mitosis
- therefore it becomes INACTIVATED
HENCE ANS:
- fewer
- more
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