Section 2: Cell Structure & Function Flashcards
Central dogma
DNA –transcribed–> RNA –translated–> Protein
DNA: heritable material
RNA: intermediary / messenger
Proteins: workers
Prokaryote vs eukaryote cell
Both have: Plasma membrane Cytosol DNA RNA Protein Ribosomes
Eukaryotic cells:
Membrane-bound organelles
Much larger
Prokaryote cells:
Lack membrane-bound nucleus
Cytoplasm - description + major organelles
Everything inside the plasma membrane except for the nucleus
Endomembrane system
Mitochondria
Ribosomes
Endomembrane system
Consists of: Nucleus Endoplasmic reticulum (smooth and rough) Golgi apparatus Lysosomes
Along with plasma membrane, they work together to package, label, and ship molecules
Plasma membrane
A selectively permeable barrier controlling passage of substances in and out of cell
Double layer of phospholipids with embedded proteins
Physical barrier separating inside and outside of cell
Body and fats - hydrophilic and hydrophobic
Much of our body is hydrophilic (water-loving)
Fats are hydrophobic (water-hating), so tend to cluster together to exclude water
Fats in cell membrane provide barrier to water
Phospholipid
Hydrophilic polar heads (phosphate)
Hydrophobic lipid tails (fatty acids)
Arranged as double layer around cytoplasm - tail to tail
2 sheets/double layer naturally forms a water-excluding membrane
Plasma membrane proteins
Mediate movement of hydrophilic substances
Often amphipathic
Allow cell-cell identification and facilitate intercellular communication
Some proteins may form channels - a pathway through the protein for hydrophilic things to go through
Integral proteins
Peripheral membrane proteins
Define amphipathic
Have both hydrophilic and hydrophobic regions
Integral proteins
Embedded (partially or fully) into membrane
Transmembrane: goes through both layers of cells
Peripheral membrane proteins
Associated with membrane, but not actually embedded in it
What plasma membrane proteins do, i.e. types of plasma membrane proteins
Transport - channels may be general or selective, gated or not, passive or require energy
Enzymatic activity - carry out chemical reaction, may be part of a team of enzymes
Signal transduction - external signaling molecule causing transduction of information to inside of cell
Cell-cell recognition - use of glycoproteins as molecular signatures of extracellular side of cell
Intercellular joining - e.g. junctions
Attachment to cytoskeleton and ECM - e.g. fibronectin mediates contact between cell surface integrins and ECM facilitates movement
Cell-specific (spatial) and dynamic (temporal) repertoire of membrane-bound proteins: depends on job of cell, and what’s happening in the cell at that time
Glycoproteins
Carbohydrate + protein
Fluid Mosaic model
The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
Nucleus
Largest organelle
Enclosed by nuclear envelope
Entry and exit through nuclear pores
Functions:
- House/protect DNA in eukaryotic cells
- Make RNA and assemble ribosomes
- Nucleus and cytoplasm separate –> molecule segregation to allow temporal and spatial control of cell function
Nuclear envelope
Double lipid bilayer
Continuous with rough ER
Nucleolus
rRNA production
Assembly of small and large subunits of ribosomes
In the nucleus: DNA (deoxyribonucleic acid)
The nucleic acid that encodes phenotype
Must be packed to fit into nucleus:
DNA wrapped 2x around group of 8 histones to form nucleosomes, collectively known as chromatin
As cell prepares for cell division, condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes
Most of the time, DNA present as chromatin and chromatin fibres
Chromosome
Comprised of many genes
Gene
A DNA segment that contributes to phenotype/function
Humans - diploid
2N = 46
23 pairs of chromosomes, one from each parent
22 autosomes, 2 sex chromosomes
Packaging of nucleus
All DNA in one cell stretches out to ~2m
Accessibility determined by extent of coiling
Condensed chromosomes easier to organize than chromatin
Ribosomes
2 subunits, small and large made of rRNA in complex with many proteins
No membrane - would be inefficient
Function: protein production
Found in 2 places within cell:
- Free in cytoplasm - making proteins to be used in cytosol
- Attached to rough ER - making non-cytosolic proteins/endomembrane
rRNA
Ribosomal RNA
Subunits assemble in nucleolus, leave through nuclear pores
Endoplasmic reticulum
An extensive network of tubes and tubules, stretching out from nuclear membrane/envelope
Two types: rough and smooth
Rough ER
Continuous with nuclear envelope
Dotted with attached ribosomes
Main function is production of:
Secreted proteins
Membrane proteins
Organelle proteins
Rough ER - proteins
Proteins enter lumen within rough ER for folding
Rough ER membrane surrounds protein to form transport vesicles destined for golgi
Smooth ER
Extends from rough ER
Lacks ribosomes - doesn’t make proteins
Major function:
Housing unit for proteins and enzymes
Synthesizes lipids
Storage of cell-specific proteins (not all cells make all proteins)
Produces sex hormones
Functions vary greatly from cell to cell - very cell/tissue-type specific
Golgi apparatus/complex/body - description, function, formation of…
The ‘warehouse’
Made up of 3-20 cisternae, stacked on top of one another
Modify, sort, package and transport proteins received from rough ER using enzymes in each cisternae
Responsible for exocytosis of proteins from cell
Formation of: Secretory vesicles (proteins for exocytosis) Membrane vesicles (PM molecules) Transport vesicles (molecules to lysosome)
Cisternae
Flattened membranous sacs
Secretory cells have…
Extensive golgi complexes, e.g. goblet cells
Golgi apparatus: to destination
Each cisternae contains enzymes of different functions
Proteins move cis to trans from sac to sac
Mature at the exit cisternae
Travel to destination
Modifications occur within each sac (formation of glycoproteins, glycolipids and lipoproteins
Lysosomes
Contain powerful digestive enzymes
Vesicles formed from golgi body
Membrane proteins pump H+ in to maintain acidic pH
Main function is digestion of:
- Substances that enter a cell
- Cell components, e.g. organelles - autophagy
- Entire cells - autolysis
Once digested, all building blocks are recycled
Lysosomal storage disorders
Failure of a single lysosome enzyme can cause severe disease
Gaucher metabolic disorder
Lysosomal storage disorder
A particular lipid (glucocerebroside) is poorly degraded
Results in severe phenotype in humans
Mitochondria - main function
Generation of ATP through cellular respiration
Mitochondria are made up of…
Outer mitochondrial membrane
Inner mitochondrial membrane, with folds called cristae
Fluid filled interior cavity, called mitrochondrial matrix
Mitochondria and energy
The more energy a cell requires, the more ATP it must make, the greater number of mitochondria present
Transfer of phosphate to another molecule provides ______
Energy
ATP
Adenosine triphosphate - our energy currency
Cytoskeleton
Structural support system of cell
Fibres of filaments that help to maintain the size, shape, and integrity of the cell:
- Act as scaffolding across cell
- Involved in intracellular transportation and cell movement
Three types of fibers (smallest to largest):
Microfilaments (dynamic - assembled and disassembled as required)
Intermediate filaments
Microtubules (dynamic)
Cytoskeleton: Microfilaments - description
Diameter: 7nm
Comprised of actin molecules assembled in two long chains, twisted around each other
Found around periphery and lining the interior of cell
Cytoskeleton: Microfilaments - functions
Bear tension and weight by anchoring cytoskeleton to plasma membrane proteins
Promote amoeboid motility if required, e.g. macrophage
Cytoskeleton: Intermediate filaments - description
Diameter: 8-12nm
Comprised of diverse range of different materials, e.g. keratin
Found in cytoplasm of cell
Often the most permanent of cytoskeleton
Cytoskeleton: Intermediate filaments - functions
Bear tension and weight throughout cell
Act as scaffold for cellular organelles
Cytoskeleton: Microtubules - description
Diameter: tubular structure, 25nm with central lumen of 15 nm diameter
Comprised of tubulin dimers (alpha and beta), coiled, to form a tube
Extends from centriole into cytoplasm/nucleus
Cytoskeleton: Microtubules - functions
Support cell shape and size
Guide for movement of organelles, e.g. vesicles from Golgi to membrane
Chromosome organisation - cell division
Support and movement of cilia/flagella
Energy process
ATP –> ADP –> Phosphate (transferred to another molecule)
Major categories of fuel
Carbohydrates - broken down to simpler sugars
Proteins - broken down to amino acids
Fats - broken down to simple fats
Which are then absorbed
Main steps of cellular respiration
Glycolysis (cytosol)
Pyruvate oxidation (mitochondrial matrix)
Citric acid/Krebs cycle (mitochondrial matrix)
Electron transport chain and chemiosmosis (oxidative phosphorylation) (proteins within inner membrane)
C6H12O6 + 6O2 –> 6CO2 + 6H2O + Energy
Electron transport chain - FADH2 and NADH
FADH2 and NADH are electron donors in the electron transport chain
Citric acid cycle intermediates
Used in other metabolic pathways
A series of reactions: product of first reaction is the substrate for the next
Acetyle CoA –> Citrate –> α-Keto-glutarate –> Succinyl CoA –> Malate –> Oxaloacetate (cycle)
Substrate phosphorylation
ATP is generated by direct transfer of a phosphate group to ADP
Glycolysis and citric acid cycle make ATP via this process
Oxidative phosphorylation
ATP is generated from oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping protons
ETC and chemiosmosis
Oxygen and cyanide
Oxygen is the final electron acceptor
Cyanide blocks passage of electrons to O2 = death of cell
Cellular respiration is versatile
Energy can be derived from more than just glucose
Fats, proteins, and more complex carbohydrates also generate ATP
Monomers enter glycolysis and citric acid at different points
Control of cellular respiration - phosphofructokinase
Can limit rate of glycolysis
Inhibited by citrate and ATP, i.e. products of cellular respiration
Stimulated by AMP - accumulates when ADP not phospho to ATP
Control of cellular respiration - feedback
Negative feedback control is integral to control ATP production
Homeostasis generally depends on negative feedback mechanisms, but can be impacted by on positive feedback mechanisms
Negative feedback: more results in less, e.g. blood glucose
Positive feedback: more results in more e.g. blood clotting
Homeostasis - increasing blood glucose level
Receptors - beta cells in pancreatic islets –>
Secrete insulin –>
Effectors - all body cells –respond with–>
Increased rate of glucose transport into target cells,
increased rate of glucose use and ATP generation,
increased conversion of glucose to glycogen –>
Homeostasis restored by decreasing blood glucose level
Homeostasis - decreasing blood glucose level
Receptors - alpha cells in pancreatic islets –>
Secrete glucagon –>
Effectors - liver, skeletal muscle, adipose cells –respond with–>
Increased breakdown of glycogen to glucose (in liver, skeletal muscle) –>
Homeostasis restored by increasing blood glucose level
Homeostasis of blood glucose - produced by? and function?
Insulin:
Produced by beta cells of islets of Langerhans in pancreas
Function - promote glucose uptake into cells (for ATP production or storage in liver)
Glucagon:
Produced by alpha cells of islets of Langerhans in pancreas
Function - stimulates breakdown of glycogen to increase blood sugar levels
What happens if you lose the function of insulin
No glucose in cells
No ATP from glucose
No glycogen for ‘harder times’
Diabetes mellitus
The ability to produce or respond to the hormone insulin is impaired
Results in abnormal metabolism of carbohydrates and elevated levels of glucose in blood
Symptoms: vision changes, fatigue, frequent urination, tingling hands/feet
Carbohydrates broken down to…
Simple sugars through digestive system
What is NADH
An electron carrier
Purpose of electron carriers
Transport electrons, e.g. to reactions in mitochondria
Glucose can transfer across ____ into ______
Membranes into bloodstream
Where is glycogen typically stored
Liver and skeletal muscles
How many ATPs per second in one cell does cellular respiration generate?
10 million ATPs per second
Glucagon vs glycogen
Glucagon acts on glycogen
Lipid chain length
Can be different lengths –> dictates fluidity of membrane
Lipid chain saturation
Can be saturated or unsaturated –> dictates structure
Nuclear pores
Channels; tightly regulated
Plasma membrane - hydrophobic or hydrophilic
Part of protein inside membrane must be hydrophobic so they’re able to interact and pass through the hydrophobic part of membrane
Part of protein outside membrane must be hydrophilic as they will be interacting with water
Chromatin vs chromosomes
If wanting to make RNA and proteins, must be able to access - hard to access large portions of genome (in chromosome), so easier to access chromatin as it’s slightly more relaxed
Without functioning free ribosomes…
Production of proteins destined for use in cytoplasm would be impaired
Without a functioning Golgi apparatus…
Protein modification would be impaired
Without functioning lysosomes…
Autophagy and autolysis would be impaired
Genotype vs phenotype
Genotype: an organism’s hereditary information
Phenotype: actual observable or physiological traits
Our genotype and its interaction with the environment determines our phenotype
Gene expression
The process of going from DNA to a functional product (typically protein)
Highly regulated - not by chance, doesn’t occur spontaneously
DNA
The heritable material that is used to store and transmit information from generation to generation
RNA
Acts as a messenger to allow info stored in DNA to be used to make proteins
Proteins carry out…
Cellular functions
Gene expression - main steps
Transcription of RNA from DNA
Processing of pre-mRNA transcript into mature mRNA
Translation of mRNA transcript to a protein
Gene expression - types of proteins
Housekeeping (commonly used) proteins:
Continuously produced from DNA
Protein and mRNA present in large quantities (e.g. tubulin)
Typically have long half life in cells
Other proteins produced in response to stimuli as required:
Cell signalling (e.g. ligand binding a cell surface receptor, or activating an intracellular receptor)
Signal transduced and may enter nucleus to active transcription
Results in production of a short-lived protein to carry out the required function
Transcription - main steps
Initiation - polymerase binds to promoter
Elongation - moves downstream through gene transcribing RNA
Termination - detaches after terminator reached
DNA vs RNA bases
DNA: A, T, C, G
RNA: A, U C, G
Exons
Coding regions (inc UTRs)
Introns
Non-coding regions intervening exons
UTR
Untranslated regions at 5’ and 3’ ends
End up in mature mRNA but not part of protein
Spliceosome
A large complex of proteins and small RNAs
Alternative splicing
A process by which different combinations of exons are joined together, resulting in the production of multiple forms of mRNA from a single pre-mRNA
Allows for multiple gene products from the same gene
Protein sequence determines…
Amino acid final structure
Structure determines function
Translation: main steps
Initiation
Elongation
Termination
How do codons form amino acids
Codons are translated into amino acids
Where is tRNA and mRNA held
Within ribosomes to enable the formation of polypeptides
Ribosome binding sites
mRNA binding site
A site - holds ‘next-in-line’ tRNA
P site - holds tRNA carrying the growing polypeptide
E site - tRNAs exit from here
tRNA
The physical link between mRNA and amino acid sequence of proteins
Initiation tRNA
tRNA carrying methionine (Met)
Translation - elongation
Codon recognition
Peptide bond formation
Translocation
How are properties of amino acids determined
Side chains (R groups) determine properties of each amino acid 20 standard amino acids
Amino acids - primary structure
Determined by DNA sequence Held by covalent bonds between amino acids (strongest bonds out of all structures) Starts to form secondary structures as soon as it leaves the ribosome Reads N (amino end) to C (carboxyl end)
Amino acids - secondary structures are held by…
Held by weak H bonds to form alpha helix and beta sheets
Amino acids - tertiary structures
3D shape stabilised by side chain interactions
Amino acids - quaternary structures
Multiple proteins associate together to form a functional protein
(not all proteins do this, but all form secondary and tertiary structures)
Where is the signal peptide found
At N terminus of protein
SRP
Signal Recognition Particle
What happens when completed polypeptide folds into final conformation
A secretory protein (e.g. insulin) is solubilised in lumen, while a membrane protein remains anchored to the basement. Both then go to the Golgi via vesicles for further maturation
Signal peptides direct ribosomes to RER - steps
- Polypeptide synthesis begins
- SRP binds to signal peptide
- SRP binds to receptor protein
- SRP detaches and polypeptide synthesis resumes
- Signal-cleaving enzyme cuts off signal peptide
- Completed polypeptide folds into final conformation
Post-translational modifications
Where translation is complete, but protein may not yet be functional
e.g. Phosphorylation
Some occur within Golgi, others in cytosol
Modification errors could lead to non-functional proteins
What can post-translational modifications do
Confer activity (e.g. phosphorylation or enzyme cleavage) Ability to interact with other molecules (e.g. biotinylation, methylation) Direct to particular locations (e.g. ubiquitination)
Mutations can affect…
The structure and function of a protein
DNA level mutations can affect…
50-100% of downstream products from cells carrying that mutation (because we have two alleles)
Types of effects of altered DNA sequence
Minor, none, or positive
Germ line - can affect many cells and be catastrophic
Local - during cell division, not whole body - local effects
Large vs small scale alterations
Large - chromosomal rearrangements
Small - one or a few nucleotides altered
Point mutations can be…
Substitutions - where one base is replaced by another; can have minimal or major effect
Insertions/deletions - can cause a frameshift; can have major effect if within coding sequence
Polypeptide
Made up of many peptides
Promoters vs terminators
Promoters - upstream
Terminators - downstream
Which way does DNA read
From 5’ to 3’ end
Template strand (3’ to 5’) used so it can create a 5’ to 3’ RNA
Non-template strand 5’ to 3’
TATA box
A particular protein to a particular sequence within the promoter
Transcription initiation complex
RNA polymerase
Makes polymer of RNA
During termination of transcription, RNA polymerase catalyses phosphate diester bonds, which makes RNA stay together when coming off as a single strand
Phosphor-diester bonds - purpose
Hold RNA together
Proteins - isoforms
Most proteins that exist don’t only have one version of themselves - often have different isoforms
Codon
3 codons from mRNA = 1 amino acid
Mutations in DNA change…
Change shape of resulting protein –> change ability to do its job
tRNA shape
Looped structure, where one of the loops forms an anti-codon which binds to the relevant mRNA codon
What is tRNA
The physical link between mRNA and the protein sequence
Start and stop codon(s)
Start codon: AUG
Stop codons: UAG, UAA, UGA
Must be in frame
Bonds between amino acids
Ribosomes help form covalent bonds between amino acids
Types of amino acid proteins
Hydrophobic
Hydrophilic
Hydrophilic - negatively charged
Hydrophilic - positively charged
Translation - endomembrane system
Vesicles are transferred from one part of the endomembrane system to another, and eventually end up on plasma membrane
How do free ribosomes know when they need to be in rough ER?
At the end of terminus, there’s a signal peptide which can be detected by SRP, which tells the peptide it needs to be made in RER
What happens if transcription doesn’t function properly
If transcription was on strike in ONE CELL within a tissue, there would be no RNA made from that cell
OR
If transcription had not quite enough for ONE TRANSCRIPTION FACTOR, then likely other transcripts are still made in that cell. Not enough, but can be compensated
If folding happened incorrectly…
Protein may not be able to function normally
Depends on scale of error - might not be catastrophic
What is found in cytosol?
Organelles, water, dissolved solutes, suspended particles
What is cytosol also known as
Intracellular fluid
Apoptosis
Programmed cell death
Oxidation reactions can produce…
Hydrogen peroxide (H2O2), which can be broken down by catalase to form H2O in peroxisomes
Why do cells communicate
They need to be able to respond as a cell, and as part of a whole tissue
They respond to signals from other cells and from the environment
Signals are often chemical, but can also be light, taste, smell etc.
Types of secreted signals
Local signalling
Long distance signalling
Secreted signals - local signalling
Signals act on nearby target cells
- growth factors such as fibroblast growth factor (FGF1 - paracrine)
- neurotransmitters such as acetylcholine (Ach - synaptic)
Secreted signals - long distance signalling
Signals act from a distance
- hormones produced by specialised cells travel via circulatory system to act on specific cells
- e.g. insulin from pancreatic beta cells bind to insulin receptors, initiating a cascade, resulting in glucose uptake
Endocrine system
Cell signalling - main steps
Reception
Transduction
Response
Receptors are _____
Specific
Human body simultaneously sends out many different chemicals and molecules, all aimed at eliciting specific responses, BUT only the target receptor on the target cell will interact with that signal/ligand and use it to activate signal transduction pathways
Where does the specificity of receptors come from?
3D molecular shape of proteins involved
Structure determines function
Exquisite control of receptors is possible
Only certain cells at certain times will have the particular receptors, so while the signal might be widespread, the transmission of the signal only occurs where needed
Main types of receptors
Intracellular receptors
Membrane-bound/cell surface receptors
Intracellular receptors
Primary messenger is generally hydrophobic and/or small - lipid soluble, can cross PM
Least common method of signalling
e.g. testosterone, estrogen, progesterone, thyroid hormones bind to receptors in cytoplasm and move to nucleus as a complex
Membrane-bound / cell surface receptors
Primary messenger is generally hydrophilic and/or large - need help to cross PM
Most common method of signalling
e.g. G protein coupled receptor, ligand-gated ion channel, receptor tyrosine kinase
G-protein coupled receptors (GPCRs)
Transmembrane proteins - pass PM 7 times
Hundreds of different GPCRs exist
Many different ligands
Diverse functions, e.g. development, sensory reception
G proteins
Molecular switches either on or off depending on whether GDP or GTP is bound
G-protein coupled receptors - steps
- At rest, receptor is unbound and G-protein is bound to GDP. Enzyme is in an inactive state.
- Ligand binds receptor (causing conformational shape change), and binds G protein. GTP DISPLACES GDP. Enzyme is still inactive. Shape alters.
- Activated G protein dissociates from receptor. Enzyme is activated to elicit a cellular response
- G protein has GTPase activity, promoting its release from enzyme, reverting back to resting state.
GPCRs - what determines function?
Conformational changes determine function
Which body system relies heavily on ligand gated ion channels?
The nervous system
- released neurotransmitters bind as ligands to ion channels on target cells to propagate action potentials
Protein kinases
Enzymes that transfer a phosphate group from ATP to another protein
Typically, this activates the protein
Signal transduction pathways
Signals can be relayed from receptors to target molecules within the cell via a ‘cascade’ of molecular interactions
e.g. series of protein kinases each adding a phosphate to the next kinase
Activates protein kinase which was inactive
Active 1 activates inactive 2, etc.
Last one in pathway of kinases is able to activate an inactive protein, which is then able to confer the actual cellular response
Phosphatases
Enzymes that dephosphorylate (remove phosphate), rendering the protein inactive, but recyclable
What are typically phosphorylated?
Serine or threonine
This means mutations affecting these residues could be detrimental
Second messengers
Another small molecule included in the cascade, e.g. cAMP and Ca2+
Second messengers- cAMP
Links to GPCR
Activated enzyme is adenylyl cyclase
Activated adenylyl cyclase converts ATP to cAMP
cAMP acts as a second messenger and activates downstream protein (coud be start of a phosphorylation cascade)
Second messenger - calcium
Low Ca2+ conc inside cell
High Ca2+ conc outside cell
Maintenance of conc via calcium pumps is important as high Ca2+ conc can damage cells
- out of cell
- into ER
- into mitochondria
Ca2+ and IP3 in GPCR signalling
Activated protein is phospholipase C, which cleaves PIP2 (phospholipid) into DAG and IP3
IP3 diffuses through cytosol and binds to a gated channel in ER
Calcium ions flow out of ER, down conc gradient, and activate other proteins towards a cellular response
Many steps in cellular signalling because…
Amplifies the response
Provides multiple control points
Allows for specificity of response (temporal, spatial) despite molecules in common
Allows for co-ordination with other signalling pathways
Cellular response includes activation or regulation of…
Gene expression
Turning off cellular responses
All signals are for a limited time; activation usually promotes start of deactivation so that signal is of short period of time, ensuring homeostatic equilibrium
Cell ready to respond again if required
cAMP broken down by phosphodiesterase (PDE)
Glycogen
A long term energy store in liver and skeletal muscle
Glycogen breakdown results in glucose 1-phosphate
Glucose 1-phosphate is then converted to glucose 6-phosphate, which can be used in glycolysis to generate ATP
Paracrine vs synaptic signalling
Paracrine: where cell releases signals to target nearby cells, e.g. blood clotting
Synaptic: similar to paracrine signalling, but only occurs between cells with synapse
Somatic cell division
Mitosis
Diploid (2n) to diploid (2n)
Reproductive cell division
Meiosis
Diploid (2n) to haploid (1n)
Why do somatic cells divide
Growth and development, tissue renewal
Results in two daughter cells genetically identical to the parent cell
Do all somatic cells divide
Most, but not all, some a lot more than others
e.g. muscle cells don’t divide
What are somatic cells doing most of the time
Going about their functions in G1 of interphase
Eukaryotic cell cycle - mitotic phase
Mitosis + cytokinesis Prophase (early and late) Metaphase Anaphase Telophase and cytokinesis
When does cytokinesis begin
Anaphase, where it starts to pinch in
Mitosis - daughter cells
Genetically identical to parent cell
2n to 2n
Key regulatory molecules for G2 checkpoint
Cyclin: a protein that fluctuates throughout the cell cycle
Cyclin dependant kinase (Cdk): a kinase that is activated when attached to a cyclin
M-phase promoting factor (MPF): a cyclin/Cdk complex - phosphorylates many other proteins, allowing mitosis to commence
G1 checkpoints
Checks if:
DNA is undamaged
Cell size and nutrition is okay
Appropriate signals are present
If not - exit to G0
M checkpoints
Checks if all chromosomes are attached to signals
Within mitosis itself
Final point prior to anaphase and telephase
Checkpoints of cell cycle rely on…
Cell signalling
What could happen if cell cycle checkpoints don’t work
Could result in uncontrolled cell growth –> tumours
DNA changes can be…
Small scale alterations (point mutations)
Gain/loss/translocation of chromosomes/genes
DNA changes can be the result of…
Acquired changes:
Affects specific cells
Viruses, UV damage, drugs, treatments
Inherited changes:
Affects all cells
Susceptibility genes
In both acquired and inherited DNA changes, altered protein function can result, which may lead to loss of cell cycle control
In cancer, genes affected by DNA changes are often…
Proto-oncogenes:
Genes that stimulate cell proliferation
Pressing the ‘accelerator’
Activation
Tumor suppressor genes:
Genes that keep proliferation in check
Loss of ‘brakes’
Deactivation
Both result in uncontrolled cell growth (tumour)
Meiosis
Occurs in gonads
Produces gametes which are haploid (single set of 23 chromosomes)
Fertilisation then restores the diploid number of chromosomes (2n)
Produces genetically different daughter cells from parent cell
Stages of meiosis
Meiosis I:
Prophase I (synapsis and crossing over, tetrads form)
Metaphase I (pairs of homologous chromsoomes)
Anaphase I (sister chromatids remain attached)
Telophase I
Meiosis II: Prophase II Metaphase II Anaphase II Telophase II
Meiosis II vs mitosis
Very similar, except meiosis II is not preceded by DNA replication
Sources of genetic variation
Independent assortment at metaphase I
Crossing over at prophase I
Fusion between two gametes
How would you sample for DNA from tumours
Isolate the DNA from the tumour itself
Coronavirus lock and key
ACE2: Angiotensin-converting enzyme 2 -
cellular receptor
S protein: Surface spike glycoprotein (S protein)
ACE2 in our respiratory tract is the lock, S-protein on the virus is the key
How does DNA polymerase III enter the nucleus from the outside
Primary active transport
A frequent problem in cancer cells is that cell division happens without the chromosomes being fully packed. This could be a problem with the formation of…
Nucleosome, chromatid, or chromatin fibres
Improperly formed intermediate filaments cause…
Abnormally shaped nuclear envelope
What cells have multiple nuclei
Skeletal muscle cells
Nucleolus is formed by…
DNA, RNA and proteins
Water molecules that move into the nucleus enter via…
Passive diffusion
When are chromatids found in a cell
Just prior to and during cell division
What do you find between nucleosomes
Linker DNA
Where does transcription and translation occur
Transcription: nucleus
Translation: ribosomes
Pathway from production to membrane insertion of Na+ channel?
Translation on rough ER –> transport vesicle –> Golgi complex –> secretory vesicle –> plasma membrane
To have an increase in protein production, there is likely to be an increase in…
Transcription of oncogenes in the nucleus
In a phosphorylation cascade, protein kinases ____ proteins by ______ them, while
phosphatases _____ proteins by ______ them
activate, phosphorylating, inactivate, dephosphorylating
Why people feel ‘wired’ after coffee
Caffeine blocks the action of a phosphodiesterase which breaks down a second messenger released after adrenalin activation
Sickle cell disease - DNA mutation
Substitution
Which protein is often mutated in cancer cells
RAS (type of proto-oncogene)
Mutated tumour suppressor protein
If DNA replication is incomplete and protein is activated at G2 checkpoint, but cell progresses to enter M phase, activated protein is most likely to be a mutated tumour suppressor protein
Efferent pathway
Information flowing away from the control centre
Synovial fluid
ECM found in joints
Nervous system regulates homeostasis in the body through _____
Neurotransmitters
Cytokinesis
Division of cytoplasm
Happens after mitosis / meiosis I
Cleave furrow is formed by which cytoskeleton?
Microfilaments
S phase time
The replication of chromosomes in S phase takes a specific amount of time that can’t be increased
Brush border refers to…
Microvilli
The initial structure formed as a polypeptide synthesised in a ribosome is…
A polypeptide chain of unbranched polymers, held tightly together by peptide bonds
Insulin is secreted by…
Endocrine cells
Which part of skin are fibroblasts found
Dermis - not epidermis
Which fibrous protein commonly forms part of the cytoskeleton of the cell
Keratin
Which structure of the cell stores the second messenger critical for muscle contraction
Smooth ER
If a protein is recognised by a Signal Recognition Particle…
That protein might function in the fluid of the extracellular matrix, as protein is sorted via the cisternae of the Golgi complex because of the SRP
