Unit 1 Cells Flashcards
Who is NOT involved in developing the Cell Theory?
Venter
The individuals who did contribute were Schleiden, Schwann, Virchow
T/F? Eukaryotic and prokaryotic cells are similar in that they both contain membranous compartments.
False
What would we expect to find in yeast?
Nucleoid, nucleus, membrane-bound organelles, linear chromosomes
and circular chromosomes
Which type of microscopy is most appropriate to observe endoplasmic reticulum in plant cells?
TEM
You just discovered a new species of thermoacidophile. Which characteristics would you expect to find in this organism?
Nucleoid, membrane-bound organelles, unusual metabolic strategy and a nucleus.
What type of bond secures secondary structure in a polypeptide?
Hydrogen bond
A polymer is composed of multiple monomers.
True
An amphipathic molecule has?
a hydrophobic and a hydrophilic region.
A molecule has a chemical structure of C7H14O7. This molecule is likely a:
carbohydrate
A liquid that has positive and negative charges can be described as hydrophobic.
False
What is NOT synthesized by plant cells?
Glycogen
Which is NOT an example of a polysaccharide?
Glucose
If you were to describe the width of a membrane, which units are most likely to be used?
Nanometers
T/F? A cis unsaturated fatty acid chain will have a considerable “bend” in its structure.
True
What is NOT an example of a polysaccharide?
Glucose
The amino acids in the transmembrane domain of an integral membrane protein likely have side chains that are:
Hydrophobic
Why is cell size limited?
As a cell grows, the plasma membrane surface area does not increase at the same rate as the cell volume.
What type of protein penetrates into the hydrophobic region of a phospholipid bilayer?
Integral and Transmembrane
T/F? Water will diffuse directly through the lipid bilayer.
False
T/F? Potassium ions (K+) will diffuse directly through the lipid bilayer.
False
T/F? The cytoplasmic leaflet of a lipid bilayer touches the cytoplasm.
True
What is NOT a component of membranes?
Triglycerides
T/F? A liquid that has positive and negative charges can be described as hydrophobic.
False
Where are ribosomes synthesized?
Nucleolus
Transcription
occurs in the nucleus & in ribosomes
T/F? Ribosomes that are docked on the surface of the rough ER will feed the newly made protein into the ER lumen as it is being synthesized.
True
Nuclear envelope
consists of a double-membrane
Tubulin is a protein that makes up microtubules in the cytoplasm. It is synthesized by ribosomes located:
on rough ER membranes.
The nuclear lamina
is composed of protein
Translation
involves linking amino acids together via hydrogen bonds, occurs in ribosomes & nucleus, and requires mRNA.
T/F? Phospholipids rotate and move laterally within a leaflet at a very high rate of speed.
True
Insulin is a protein hormone that is secreted from pancreatic cells. Insulin is synthesized by ribosomes located where?
on rough ER membranes
What components are apart of the endomembrane system?
Smooth & rough endoplasmic reticulum, golgi, mitochondria, and lysosomes
T/F? Vesicles containing modified proteins bud off the trans face of the Golgi.
True
T/F? There is a constant flow of proteins and lipids between organelles of the endomembrane system.
False
T/F? The cis face of the Golgi is closest to the endoplasmic reticulum.
True
T/F? Proteins move between organelles of the endomembrane system, but lipids do not.
False
Where is chromatin located?
Nucleus
T/F? Monomers are single units.
True
T/F? Membranes that are enriched in saturated fatty acids will be more fluid.
False
Microtubules grow from the ___?
centrosome, which is composed of centrioles.
Mitochondria
are the site of ATP synthesis
Males afflicted with Kartagener’s syndrome are sterile because of immotile sperm, and often suffer from lung infections. This may be due to a mutation in which protein?
Tubulin
Which of the following contains peptide bonds?
myosin
Microtubules
are polar structures, are the largest element of the cytoskeleton, are involved in cytokinesis, and can fall apart quickly.
grow out of centrosomes, act as railway for motor proteins
‘9-2’ structure
T/F? Ribosomes are the site of protein synthesis (translation), forming peptide bonds between amino acids via hydrolysis reactions
False
Who developed a self-replicating synthetic cell?
Venter
Which molecules are amphipathic?
Phospholipids and cholesterols
Which of the following chemical features are found in a phospholipid?
Three & two fatty acid chains, R-group, amino group and a phosphate group
T/F? The terms “cell membrane” and “plasma membrane” both refer to the exterior membrane that surrounds the eukaryotic cell
True
Mitochondrial ribosomes are located
in the matrix
T/F? The cytoskeletal elements are membrane-bound organelles
False
What is found at the base of a flagellum?
Basal body
Name six proteins?
Keratin, myosin, lamin, kinesin, actin, tubulin
T/F? Proteins are polymers.
True
What type of bond would you find in a histone?
Peptide
The amino acids in the transmembrane domain of an integral membrane protein likely have side chains that are:
Hydrophobic
T/F? Lipids are polymers
False
T/F? Mitochondrial DNA is located in the matrix.
True
Where are ribosomes located in eukaryotic cells?
ER lumen, cytoplasm, plasma membrane, rough endoplasmic reticulum membrane, and lysosomes
Which features do intermediate filaments and microfilaments have in common?
They are both polar structures, smaller than microtubules and have associated proteins.
According to the endosymbiont theory…?
mitochondria evolved when an ancient eukaryote endocytysed a prokaryotic cell.
Which features do microtubules and microfilaments have in common?
They both have associated proteins, are polar structures, are very rigid and rarely fall apart and they are both smaller than intermediate filaments.
What does the endosymbiont theory explain about mitochondria?
That they have circular DNA, how Golgi-resident enzymes are shipped backwards via retrograde transport, are approximately the same size as bacteria, and have ribosomes that resemble prokaryotic ribosomes.
T/F? A molecule that is amphipathic has both a positive and a negative region within the same molecule.
False, not positive or negative it is that it has a polar or nonpolar side.
Which of the following is NOT a feature of phospholipids?
a) Three fatty acid tails
b) phosphate group
c) Glycerol
d) Amphipathic nature
e) Polar head group
a) Three fatty acid tails
Which combo of biological molecule and example is correct?
a) Cellulose = disaccharide
b) mRNA = nucleic acid
c) Cholesterol = lipid
d) Enzymes = protein
e) Glucose = polysaccharide
b) mRNA = nucleic acid
c) Cholesterol = lipid
d) Enzymes = protein
Arctic char live in frigid waters. It’s expected that their cell membranes would have alot of ____ fatty acid tails.
a) Saturated
b) Unsaturated
b) Unsaturated
The amino acids are found in the a-helix of transmembrane proteins are ones with:
a) Hy- side chains
b) Hydrophobic side chains (correct)
b) Hydrophobic side chains
Which association(s) are correct?
a) Eukaryotes = membrane bound circular DNA
b) Eukaryotes = 10-30 um in diameter
c) Prokaryotes = DNA located in nucleoid
d) Prokaryotes = many membrane bound organelles
b) Eukaryotes = 10-30 um in diameter
c) Prokaryotes = DNA located in nucleoid
A protein’s primary structure:
a) Refers to sequences of its nucleic acids
b) Is stabilized by peptide bonds
c) Is impacted by hydrophobic & hydrophilic side-chains
d) Two of the above
b) Is stabilized by peptide bonds
T/F? Ribosomes that are free in the cytosol are structurally identical to the ribosomes that are bound to membranes.
True
T/F? Carbohydrate chains can be attached to proteins.
True, sugar chains are critically important for protein trafficking
Which describes the lysosome?
a) Contains hydrolytic enzymes and has a low pH
b) Contains hydrolytic enzymes and a has a high pH
c) Contains dehydration enzymes and has a low pH
d) Contains dehydration enzymes and has a high pH
e) None above
a) Contains hydrolytic enzymes and has a low pH
Membrane sugars:
a) are always located on the cytoplasmic leaflet.
b) are never associated with lipids or proteins.
c) none of the above
c) None of the above
Which of the following is synthesized in a ribosome?
a) Kinesin
b) Glycogen
c) mRNA
d) Phospholipids
e) Chitin
a) Kinesin
T/F? Microtubules are considered to be polar structures because one end has a negative charge and the other end has a positive charge.
False
The inner-most compartment of mitochondria is called?
The matrix
In which of the following would you find microtubule triplets?
a) Nuclear lamina
b) Microtubules in a ‘9+2’ arrangement.
c) Centrioles
d) Cortex
c) Centrioles
Desmosomes are?
cell to cell attachment structures.
T/F? A liposome is a single layer of phospholipids that forms a sphere and can be used as an artificial cell.
False
In which of the following would you find microtubule triplets?
a)Nuclear lamina
b)Cortex
c)Centrioles
c) Centrioles
Which of the following features are found in a molecule of ADP?
a) Ribose
b) Carboxyl group
c) Three phosphates
d) Nitrogenous base
e) Fatty acid
a) Ribose
b) Carboxyl group
e) Fatty acid
Which of the following are products of the oxidation of pyruvate?
a) FADH2
b) Oxygen gas
c) Carbon dioxide
d) Water
e) NADH
f) Acetyl CoA
All of them are products
Nicotinamide adenine dinucleotide becomes reduced when?
It gains a hydrogen atom and two electrons.
T/F? NAD+ can carry 2 electrons and 1 hydrogen atom.
True
Which of the following is NOT a product of the full oxidation of glucose?
a) Carbon dioxide gas
b) Heat
c) Glycogen
d) Oxygen gas
e) ATP
f) Water
b) Heat
e) ATP
f) Water
T/F? Anabolic reactions are endergonic; they release energy and have a positive delta G value.
False
T/F? Substrate-level phosphorylation occurs during glycolysis?
True
Which of the following processes do NOT occur in the mitochondrion?
a) Oxidative phosphorylation
b) Glycolysis
c) Electron transport chain
d) Citric acid cycle
e) Oxidation of pyruvate
f) Chemiosmosis
b) Glycolysis
c) Electron transport chain
d) Citric acid cycle
e) Oxidation of pyruvate
The complexes of the electron transport chain pump hydrogen atoms from the _________ to the _______ .
matrix | intermembrane space
FADH2 is formed during ________ and pyruvate is formed during ___________ .
citric acid cycle | glycolysis
Which of following bring electrons directly to the electron transport chain?
a) NADH
b) Acetyl CoA
c) FADH2
d) ATP
e) Glucose
f) Oxaloacetate
g) Pyruvate
all of them bring e- to transport chain
T/F? Three carbon dioxide molecules are generated via glycolysis. This is indicated by the fact that the starting molecule is glucose (6C) and the final organic compound is pyruvate (3C).
False
The electron transport chain causes protons to accumulate in the ____?
Intermembrane space
T/F? A reduction reaction occurs when a molecule has its number of electrons (and often hydrogen atoms) reduced.
False
Which of the following chemical features are found in a phospholipid?
a) Two fatty acid chains
b) Phosphate group
c) Polar head group
d) Amino group
e) R-group
f) Three fatty acid chains
g) Glycerol
b) Phosphate group
c) Polar head group
d) Amino group
e) R-group
f) Three fatty acid chains
g) Glycerol
T/F? The MOST common unit of measure to describe cell organelles is the nanometer.
True
T/F? Nucleic acids are polymers
True
Cyanide is a poison that targets the electron transport chain. It works by inhibiting the final complex in the electron transport chain and prevents electron transport to oxygen. What is a likely result of this action?
the proton motive force will be lost.
T/F? Phospholipase C is an effector enzyme that can generate two second messengers.
True
Which of the following is a transmembrane protein?
a) G Protein
b) GPCR
c) Adenylyl cyclase
d) IP3
e) cAMP
b) GPCR
d) IP3
What stimulates adenylyl cyclase?
G protein attached to a GTP
Which of the following is NOT an extracellular signalling molecule?
a) Adenylyl cyclase
b) Neurotransmitter
c) Ligand
a) Adenylyl cyclase
Many signal transduction pathways are initiated by a signal binding to a membrane receptor. Which statement about this type of signalling mechanism is correct?
a) Ligand binding may lead to the activation of a protein kinase.
b) A first messenger injected into the cytoplasm will activate the pathway.
c) A mutation in a single gene can disrupt an entire signalling pathway.
b) A first messenger injected into the cytoplasm will activate the pathway.
c) A mutation in a single gene can disrupt an entire signalling pathway.
T/F? During Receptor Tyrosine Kinase activation, the tyrosine amino acid residues are phosphorylated through the process of oxidative phosphorylation.
False
Ligands generally bind to receptors located in the plasma membrane. Which of the following ligands is the EXCEPTION to this rule?
Testosterone
A molecule consisting of a nitrogenous base, a monosaccharide, and three phosphates is most likely a(n)
a) amino acid
b) ATP
c) fatty acid
b) ATP
Which statements are true regarding a protein hormone that is secreted from a cell?
a) It’s translated by a cytoplasmic ribosome
b) It will not be involved in the secretory pathway
c) It primarily contains glycosidic bonds
d) Two of the above
e) None of the above
e) None of the above
What is not involved in the secretory pathway for protein hormones?
a) Ribosomes
b) Lysosomes
c) Rough ER
d) Secretory vesicles
b) Lysosomes
What is true of cholesterol:
a) Contain fatty acid rails, allowing it to embed into membranes
b) Four carbon rings
d) Is amphipathic
e) Does not influence membrane fluidity
f) Two of the above
f) Two of the above
b) Four carbon rings
d) Is amphipathic
T/F? Passive diffusion is when a molecule diffuses directly through the lipid bilayer (between phospholipids). It requires energy from ATP to occur.
False, passive transport doesn’t require ATP
Which chemical features are found in ATP molecule?
a) Nitrogenous base
b) Exactly 2 phosphates
c) Exactly 3 phosphates
d) Deoxyribose
e) Amino group
e) Ribose
a) Nitrogenous base
c) Exactly 3 phosphates
e) Ribose
What are the characteristics of peripheral membrane proteins?
Loosely attached to surface of membrane, primary structure stabilized by peptide bonds and made in ribosomes
Which is a protein?
a) GPCR
b) G protein
c) GTP
d) GDP
e) Two above
e) Two above
a) GPCR
b) G protein
T/F? GPCRs are transmembrane proteins that are stabilized in membranes via alpha-helix domains, while G proteins are only loosely attached to the surface of a membrane.
True
T/F? Golgi-resident enzymes carry out hydrolytic reactions.
False
T/F? Adherens junctions attach cells to its substrate below.
True
In which stage of the cell cycle do the centrosomes move to opposite poles? (G1, G2, M, S?)
M
Which of the following is responsible for cleaving the attachments between sister chromatids?
Separase
T/F? Chromosomes align near the center of the cell during metaphase.
True
Imagine that you are in a job interview for a pharmaceutical company and are asked to suggest a good mechanism for an anti-cancer drug. Which of the following mechanisms would you suggest?
a) decreased apoptosis.
b) increased tyrosine kinase receptor pathway activity.
c) decreased binding of cyclin to cdk.
c) decreased binding of cyclin to cdk.
What is Ras / What’s its function?
kicks off a phosphorylation cascade that ultimately leads to cell division, is involved in angiogenesis, is a carbohydrate.
Which features do intermediate filaments and microfilaments have in common?
They are both smaller than microtubules, They both are very rigid and rarely fall apart.
T/F? Paracrine signalling is a form of cell-to-cell communication in which a cell produces a signal to induce a response in a nearby cell.
True
Which of the following is NOT a typical function of the Golgi?
a) Translating proteins that are destined to remain in a membrane.
b) Modifying glycoproteins by the addition or removal of carbohydrates.
c) Sorting and targeting proteins into vesicles.
a) Translating proteins that are destined to remain in a membrane.
a) Pinocytosis
b) Receptor-mediated endocytosis
c) Bulk endocytosis
c) Bulk endocytosis
What’s synthetic biology?
Engineer natural biological systems
(bacteria, yeast, fungi, plants and animals) to produce desired products.
What are the three parts of cell theory?
All organisms consist of one or more cells. The cell is the basic unit of structure for all organisms. (Schleidan & Schwann)
All cells arise by division from pre-existing cells. (Virchow)
When and who made the first microscope?
1660 - Robert Hooke Mircoscope
Who’s scopes could magnify up to x300? and around what year?
1670s - Antonie van Leeuwenhoek
When was 1st electron microscope (EM) was made?
1931
Transmission Electron Mircoscope (TEM)
Penetrates through specimen
to show organelles.
Scanning Electron Mircoscope (SEM)
Scans surface of specimen to
give 3D image
Large biological molecules
Carbohydrates, proteins, lipids, nucleic acids
REVIEW: Macromolecules are formed via dehydrated rxns catalyses by enzymes
Polysaccharides…what are they/what is their purpose?
hundreds or thousands of monosaccharides linked together
purpose: energy storage or structure
Lipids
water hating, don’t form polymers, fats, phospholipids, steroid
A hydrocarbon chain with a carboxy group on end is called a ?
fatty acid
Triglycerides are composed of?
1 glycerol + 3 fatty acids
Saturated vs unsaturated
Saturated has no double bonds
Unsaturated has double bonds
T/F? Cis will form a bend, trans will not form a bend.
True
Phospholipids is composed of? Is it amphipathic?
Glycerol backbone + 2 Fatty Acids + phosphate + a small molecule
Yes, amphipathic!
(contains both a hydrophilic AND
a hydrophobic region in the same molecule)
Structure of a protein?
Polymers of amino acids linked
end-to-end in a specific sequence (amino acids, side chain R-group, carboxyl group)
Four levels of protein structure?
1st: amino acid order
2nd: 3D shape
3rd: 3D shape based on interactions between R groups
4th: multiple polypeptides
(small proteins) as a unit
Desmosomes and hemidesmosomes are what?
Desmosomes: cell to cell attachment structures
Hemidesmosomes: cell-substrate attachment structures
Nitrogenous bases?
adenine, thymine, guanine, cytosine
Structure of ATP?
nucleoside triphosphate, consisting of a nitrogenous base (adenine), a ribose sugar, and three phosphate groups
What is nucleotide composed of?
nitrogenous base, sugar and phosphate group
Surface Area to Volume ratio
Small cells have small volume, so membranes can easily keep up with internal demands..
Large cells have a larger volume, there is not enough membrane to keep up with internal demands.
What are leaflets?
cytoplasmic and exoplasmic material
NOTE: Phospholipids move side to side rapidly, but almost never flip-flop
Selective Permeability
Biological membranes are
barriers to solute movement
Passive & active diffusion
P: no energy, molecules move “down”
their gradient only (high to low concentration)
A: requires ATP, molecules move ‘up’ gradient
What is the structure of protein(s)?
polymers of amino acids
..they have an amino group and a carboxyl acid group
(see image: H-N-H middle: H-C-R, side C=O-OH)
Cellulose
structural polysaccharide, provides strength
Four main polysaccharides
Glycogen, starch, chitin, and cellulose
NOTE: Dehydration rxns remove water to bond, hydration rxns add water to remove
cell membranes
…5-10 nm thick
…Membranes are approx 50% lipid and 50% protein
…functions: storage, selectively permeable barrier (waste and products in and out), energy production (ATP) and signaling
Flippases
enzymes that flips phospholipids from one membrane to another
NOTE: Integral proteins penetrate into the hydrophobic region of the bilayer. Often called transmembrane proteins. Are α-helices and asymmetric.
What is the Na+/K+ Pump?
Integral membrane protein (transmembrane), conformational changes to exchange Na+ for K+ across the membrane.
Function: pump Na+ out and K+ in, the pump is on the cytoplasm side
Quick recap of the Na+/K+ Pump?
3 Na+ ions bind. ATP is hydrolysed and the phosphate attaches to the pump.
The binding of the phosphate causes a conformational change in the protein, and the three Na+ are released to the outside of the cell.
Two K+ are now able to bind on the exoplasmic side. The phosphate is released, causing another conformational change.
The pump is now open to the cell side again!
And the cycle repeats..! THREE Na+ are pumped across the membrane for every TWO K+
Receptor-mediated endocytosis
Ligand binds to a receptor on the cell membrane
ribsomes & protein synthesis steps
- DNA is read to make mRNA (transcription)
- mRNA leaves the nucleus
- Ribosomes read the mRNA and assemble amino acids in the correct sequence to make a protein (translation)
Ribosomes are found where?
Free in cytosol, bound to membranes (ER and nucleus), in mitochondria
Endomembrane system
Interconnected system of cytoplasmic membranes (including: nucleus, golgi, endoplasmic reticulum, lysosomes and vesicles)
How do newly made proteins move through the Golgi?
Cisternae mature through the Golgi and then Golgi-resident enzymes are moved backwards to return them to their home compartments.
lysosomes
Derived from the Golgi (and some vesicles become lysosomes)
Responsible for intracellular digestion
Phagocytosis: cell eating
Autophagy: self eating (old/damaged organelles)
The nuclear lamina does what in mitosis?
falls apart
Nucleolus make what?
Ribosomes
cytoskeleton function?
structural support, cell motility, movement of materials, mitosis and cytokinesis
Microtubules internal structure is called what?
axoneme..the “9+2 arrangement”
nine doublet microtubules and two single mircotubules
NOTE: centrosome for the axoneme is called the basal body.
cross section through cilium (9+2 arrangement)
cross section of basal body (1 centriole : 9 triplets)
microfilaments
are involved in cytokinesis, can fall apart quickly, are involved in cilia and flagella movement, are the smallest element of the cytoskeleton, and are polar structures
made of actin, 7nm, concentrated in cortex, contract muscles (when interacting w/ myosin), involved in cell division, change shape of cell, transport vesicles
intermediate filaments
Around 8-12nm, unique to animal cells, rope-like not hollow or polar, mechanical support, composed of proteins like keratin & lamins
ex. Nuclear lamina (ridgid meshwork)
Keratin is involved in attachment points between ____ or between or in ______.
cells
substrate
Anabolic
synthesis of more complex compounds, its also endergonic (i.e. require an input of energy)
Catabolic
disassembly of complex molecules, its also exergonic (i.e. release energy)
Who won Nobel prize for method of genome editing in 2020?
Jennifer Doudna and Emmanuelle Charpentier
Endergonic Reactions ______ energy
REQUIRE
Exergonic Reactions ______ energy
RELEASE
NOTE: Cellular respiration includes reduction-oxidation reactions (Redox reactions)…Transfer of electrons and hydrogen atoms from one compound to another
How do autotrophs and heterotrophs get their energy?
Autotrophs use photosynthesis to convert light energy to chemical energy (mostly glucose)
Heterotrophs (like people) eat these organic molecules and convert the chemical energy into ATP via cellular respiration
Oxidation is the ____ of electrons.
loss
Reduction is the ____ of electrons.
gain
Glycolysis
Occurs in the cytoplasm! Starts with a glucose (6C); Anaerobic (no O)
Products: 2 pyruvate, 2 ATP and 2 NADH
Oxidation of pyruvate
Both pyruvate molecules move into the mitochondrion..The reaction is catalyzed by the enzyme Pyruvate Dehydrogenase
Pyruvate -> Acetyl CoA + NADH + CO2
INFO:
Nicotinamide adenine dinucleotide (NAD+)
NAD+ = Oxidized form (no electrons attached)
NADH = Reduced form (electrons attached!)
Citric Acid Cycle
Occurs in the matrix of the mitochondrion
From one acetyl CoA entering the Citric Acid Cycle we get: 1 ATP, 3 NADH, 1 FADH2, 1 oxaloacetate, 2 CO2
…CoA group leaves! Acetyl group attaches to oxaloacetate to make citrate
…Two CO2 molecules removed!
…For each acetyl CoA that enters the cycle, 3 NADH produced!
…One FADH2 produced
…Another ATP made!
…Oxaloacetate regenerated in final reaction of cycle
INFO: mircotubules a and b dimers, plus end, protofilament, minus end - not positively or negatively charged
Oxidative Phosphorylation
The production of ATP using energy derived from redox reactions in the electron transport chain.
Electron Transport Chain
Four complexes in the Inner membrane of the mitochondrion…Series of redox reactions
Chemiosmosis
ATP Synthase: Protons (H+ ions) flowing through ATP synthase provide the energy to synthesize large amounts of ATP
Chemiosmotic Theory
The H+ gradient provides the energy to phosphorylate ADP to synthesize ATP
INFO:
Mitochondria:
- outer membrane encapsulates
- inner membrane
- folds: cristae
- space between inner and outer: inner membrane space
- space inside: matrix
INFO:
Communication occurs via extracellular messenger molecules (ligands, hormones, neurotransmitters, 1st messengers, signaling molecules)
It can occur between gap junctions & cell-cell recognition
Signalling can be local
paracrine - only cell releases signal that has effect on another cell that is very close (synaptic)
Signalling can be long-distance (endocrine signaling)
Molecules (hormones) move far away from the secreting cell (endocrine cell), through the blood to receptor cells
NOTE:
regardless of cell signalling distance, the arrival of the ligand (at a receptor - protein in cell membrane) will initiate the process of cell signaling (opening channels, or activating a gene, release hormone, cell division & death).
Cell Signalling Stage 1: Reception
…Once inside, the ligand binds to a receptor to make a complex
…Ligand-receptor complex moves into nucleus acting as transcription factor (turns on piece of DNA, producing specific protein)
…mRNA leaves the nucleus, finding a ribosome which translates the mRNA to make another protein (cellular response)
What are GPCRs?
G protein coupled receptors: peripheral membrane proteins that have 7 transmembrane domains (alpha helices), asymmetric, many are sensory receptors…named since they interact with G proteins, can bind to GTP or GDP
How are GPCRs similar to ATP?
has a different nitrogenous base, but still has a ribose and three phosphates. It can be hydrolysed to release energy.
NOTE:
If bound to GTP = inactive whereas if bound to GDP = active
How do GPCRs work?
G protein is inactive and bound to GTP, ligand binds to GPCR
the receptor changes shape so that a new GTP replaces the GDP
G protein is activated, let go of receptor and binds it to another enzyme, (activated)
The G protein will slowly hydrolyze its bound GTP, becoming GDP, and now the G protein is inactive and the cycle can start again.
Cell Signalling Stage 2: Signal transduction
Steps leading to a particular response
Phosphorylation Cascades > Second messengers relay signal to the cell’s interior > Tyrosine Kinase Receptors
What happens when there’s a problem with RAS (small G-protien)?
It allows cells to replicate uncontrollably. So all cancers have some sort of RAS system defect.
Tyrosine Kinase Receptors
Two identical receptors in the membrane, as monomers they are inactive. When ligand binds to receptor, they form a dimer. Receptor will attach P to all of the tyrosines. Once dimerized & (auto)phosphorylated the receptor becomes active so other proteins can come to it and become activated.
(overall involved in growth)
Second messengers
(not proteins!) that relay the signal to the cell’s interior
Ex. Cyclic Adenosine Monophosphate (cAMP) - flight/fight response
Many pathways are regulated by cAMP
…However, if the cell decides not necessary, phosphodiesterase shuts it off.
Phosphorylation Cascades
The activity of many proteins can be controlled by either adding or removing a phosphate group
Kinase
protein adds PO4 to another protein
Phosphatases
protein that removes the PO4 from another protein
Cell Cycle is broken into?
interphase: G1 (gap), S (synthesis), G2 (gap)
And M phase: mitosis (division of genetic material) & cytokinesis (division of cytoplasm)
S phase
Chromosomes will duplicate
Then two sister chromatids are separated during mitosis
what happens before Mitosis?
Interphase (G2) - DNA is thin and centrosomes have duplicated.
Prophase
Chromatin starts to condense and centrosomes move to opposite poles. Nuclear lamina breaks down and envelope fragments.
Prometaphase
Mitotic spindle starts to form, kinetochore microtubules capture chromosomes (attach at a protein structure called the kinetochore). Centrosomes at opposite poles, chromosomes condensed.
Mitotic spindle
microtubules radiate from each centrosome
Metaphase
Chromosomes line up along the metaphase plate, the cell will confirm there is a microtubule attached to every sister chromatid.
Anaphase
separase enzyme cleaves proteins that hold sister chromatids together. Sister chromatids are pulled to either side of the cell.
NOTE:
Anaphase A: Kinetochore microtubules get shorter, they use motor proteins. (How it can collapse and pull)
Anaphase B: Polar microtubules get longer, spindle elongates (uses kinesins). Kinesins walk and push microtubules apart.
Telophase
DNA unwinding, and new nuclear envelope forming. Spindle microtubules depolymerize.
Contractile Ring Theory
Myosin pulls a ring of actin in the cortex to “contract” the cell in a ring.
Cell Cycle Control
Checkpoints will halt the cell if needed
M checkpoint & G2 checkpoint
M checkpoint: cell ensures every sister chromatid is attached to a kinetochore molecule before anaphase occurs
G2 checkpoint: entry into mitosis depends on cyclins and Cdks
How does cell cycle control and the checkpoints relate to signalling? (Hint: Ras-MAP pathway)
Ras-MAP Pathway: if this pathway is unregulated, cells will constantly produce cyclins (when they shouldn’t) and MPF will start mitosis.
What is apoptosis? give examples of its functions.
programmed cell death
clears out cells (old or damaged)
NOTE:
Adheren Junctions..
…Cadherin proteins ‘zip’ cells together
Cancer cells have less of these proteins than normal cells leading to the spread and growth of cancer in differing areas
Examples of second messengers?
cAMP, oxygen gas
Membranes are fluid, this is critical to membrane function. Why?
Transports of solutes across the membrane, and cell to cell communication.
T/F? Catabolic reactions are exergonic; they require an input of energy and have a negative delta G value.
False
T/F? Secretion of a neurotransmitter that stimulates a neighboring neuron is an example of autocrine signalling
False
T/F? Paracrine signalling is a form of cell-to-cell communication in which a cell produces a signal to induce a response in a nearby cell.
True
T/F? Phosphorylation cascades only occur during signal transduction that is initiated by GPCR activation.
False
The integral membrane protein rhodopsin, which is used in light perception, is a protein that spans the membrane seven times. Which assumption about rhodopsin is likely correct?
a) It is likely a G protein.
b) It is composed of only hydrophobic amino acids.
c) It contains both hydrophobic and hydrophilic domains.
c) It contains both hydrophobic and hydrophilic domains.
During GPCR activation, receptor dimerize and tyrosine amino acid residues are phosphorylated.
False
T/F? Eukaryotic and prokaryotic cells are similar in that they both contain linear chromosomes.
False
You have discovered an unidentified cell that is approximately 5 microns in size. This is most likely a..?
Bacterial Cell
T/F? Metabolism refers to all rxns in a cell
NOTE:
ATP molecule splits off one of its three phosphates, becoming ADP (Adenosine di-phosphate)
Full oxidation of glucose also produces ATP
