Cell and Molecular Biology

Question 1

What is PIP2? And what is the molecular pathway?

Answer 1

It is the start of a secondary messenger cascade in the cell. Ligand binding to the GCPR causes PIP2 to be cleaved to IP3 and (DAG) diacylglycerol. It is cleaved by PHOSPHOLIPASE C

Question 2

What happens to IP3 after it is formed from PIP2 being cleaved?

Answer 2

IP3 binds to Ca2+ gated channels on endoplasmic reticulum to cause calcium to surge into cell. This increase in Ca then causes further actions through various Ca mediated mechanisms

Question 3

What happens to Diacylglycerol (DAG) after it is formed from PIP2 being cleaved?

Answer 3

DAG stays on the plasma membrane, and 2 things can happen. Can be further cleaved to form arachidonic acid. OR it can act as a secondary messenger, by activating PROTEIN KINASE C

Question 4

What are Eicosanoids

Answer 4

These are signalling molecules that are made in the plasma membrane of cells. They are generally all made from arachidonic acid.

Question 5

What are the 4 main groups of Eicosanoids

Answer 5

Prostagladins (inflammation, causes vasodilation)
Prostacyclins (Haemostasis and vasodilation, used for PAH)
Thromboxanes (causes vasoconstriction and promotes clot formation)
Leucotrienes (all about the immune response)

The first 3 of the above are known as prostanoids

Question 6

What are the prostanoids

Answer 6

This collectively is the prostaglandins, prostacyclins, thromboxanes. They are all forms of Eicosanoids produced from arachidonic acid.

Question 7

How are prostanoids produced

Answer 7

Produced from Arachiodonic acid by the COX or cyclooxygenase enzymes.

Question 8

Differences in the COX enzymes

Answer 8

COX 1 is found is tissues that continuously produce prostagladins such as the stomach mucosa. Whereas COX 2 is only induced and then expressed in sites of inflammation. So it has to be induced by bacterial products and pro-inflammatory cytokines.

Question 9

What common drugs target these Eicosanoid pathways

Answer 9

Cortisone/corticosteroids = Inhibit phosholipase and therefore reduce production
NSAIDs = Also inhibit COX and reduce production, remember older ones target COX1 and 2 both, while newer ones target COX 2 more. COX2 inhibitors are better for period pains
Aspirin = This permenanty acetylates the active site of COX enzyme, so it does not work. Low doses of aspirin therefore inhibit thromboxane production on platelets and have an anticoagulant effect before being metabolised by the liver and causing little systemic effect.

Question 10

What enzymes produce NO or nitric oxide

Answer 10

There are 3 enzymes that produce it. eNOS endothelial NO synthase, iNOS inducible NO synthase, and bNOS brain NO synthase.
eNOS is on endothelial cells and produces NO in response to shear pressures.

Question 11

How does NO act as a signalling molecule

Answer 11

NO is small so can easily diffuse into underlying SM of vessels and reacts with iron in the active site of an enzyme, guanylate cyclase to produce the intracellular mediation cGMP. The cGMP causes rapid muscle relaxation and therefore reduces BP

Question 12

How does carbon monoxide (CO) work as a messenger

Answer 12

This gas, like NO, also stimulates the guanylate cyclase enzyme. CO is produced by 2 enzymes called haemoxygenase 1 and 2. Like NO, CO is also important for maintaining vasodilation in the placenta.

Question 13

What is calmodulin

Answer 13

This is a protein found in cells. It is able to bind to Ca in order to buffers its levels in the cells. There are also calmodulin dependant protein kinases.

Question 14

What does cAMP or cyclic adenosine monophosphate do

Answer 14

This is made from ATP by the plasma membrane bound enzyme adenylate cyclase. Remember that ATP can give away a phosphate to phosphorlyate something which can alter the activity of many different enzymes.

Question 15

What does cGMP or cyclic guanosine monophosphate do

Answer 15

This cGMP is made by the guanylate cyclase enzme when it converts GTP to cGMP. Remember that this enzyme is activated by NO. And cGMP therefore causes smooth muscle relaxation
cGMP is degraded by phosphodiesterases. Sildenafil is a PDE inhibitor.

Question 16

What are the 4 main types of cell surface receptor?

Answer 16

GCPR
Ion channel receptors
Tyrosine kinase linked receptors
Receptors with intrinisic enzyme activity

Question 17

What are the 3 main types of GCPR and how do they work

Answer 17

Stimulatory GPCR: binding causes activation of adenylate cyclase which produces cAMP
Inhibitory GCPR: Cuases inhibition of adenylate cyclase
Gq GPCR: Activated phospholipase C which triggers production of IP3 and DAG from PIP2

Question 18

How is a GCPR activated

Answer 18

Binding of a ligand causes a conformational change. Causing the existing intracellular GDP to be displaced by a GTP. THis causes the alpha subunit of the GCPR to dissociate and activate the adenlate cyclase causing the conversion of ATP to cAMP. Eventually this alpha subunit will re associate with the GCPR and hydrolyse GTP to GDP to reset the GCPR

Question 19

How does an ion channel receptor work?

Answer 19

The binding of a ligand just causing a conformational change that allows ions to flow through. This therefore alters the electrical potential across the membrane. An example is the Acetycholine receptors at nmjs.

Question 20

How to tyrosine kinase linked receptors work

Answer 20

Before binding the receptor is actually 2 monomeric receptors, ligand binding causes then to fuse into a dimeric one. This causes the activation of the intracellular tyrosine kinase enzyme, which then phosphorylates the tyrosine residues on the receptor. This means that anything that binds to these phosphytyrosine residues are also phosphorylated.

TK receptors are known as the superfamily of cytokine receptors. Ligands include EPO and interferons.

Question 21

Receptors with intrinsic enzyme activity, how do they work?

Answer 21

Ligand binding to these kinds of receptors also causes dimerisation of the receptor. An example is the enzyme guanylate cyclase which makes cGMP.

Question 22

Give 4 examples of cell-cell adhesion molecules and briefly describe them

Answer 22

1) Cadherins = Hold cells together in a Ca dependant measure. They are transmembrane linker proteins with the cytoplasmis domain linked to the cytoskeleton = Actin.
2) Immunoglobulin-like molecules = These are large molecules but are generated from a small number of genes with alternative splicing. Examples are NCAMs, ICAMs, VCAM
3) Integrins = Glycoproteins that allow adhesion and communication between cytoskeleton and extracellular matrix. Can be active and inactive, like binding to WBCs on endothelium or not
4) Selectins = Mainly expressed by leucocytes, these produce only a weak bond with carbohydrate residues on cell surface. Neutrophils roll along endothelial wall with these selectins. Then bind stronger to integrins that are expressed at the site of inflammation then extravasate

Question 23

What are the 4 cell junctions, with brief description

Answer 23

1) Tight junctions = Impermeable seal between 2 cells, like in GI tract
2) Adherens junctions and desmosomes = Binds plasma membranes of adjacent cells
3) Hemidesmosomes = connect cells intermediate filaments to underlying ECM.
4) Gap junctions = Specialised channels that allow passage of small signalling molecules like Ca and cAMP. In the myometrium this is how SMs can contract together. There are lots more gap junctions in labour for example.

Question 24

What are the stages of cell division

Answer 24

G1 = Growth. Non dividing cells can go through a G0 cycle and stay in G1
S = Replication of DNA
G2 = More growth
Interphase = All of the above

Prophase = Chromosomes condense

Metaphase = sister chromatids line up in middle of cell

Anaphase = Seperate and then move to opposite poles of the mitotic spindle

Telophase = Nuclear envelop breaks down, then reforms around segregated chromosomes. Then finally the cysoplasms divides to form two daughter cells which is a process called cytokinesis.

Question 25

Give five example of cell cycle control points, and important proteins that work on these checkpoints

Answer 25

1) DNA damage check = BRCA1 and 2 are DNA repair proteins. If the damage is not repairable then cell goes under apoptosis
2) Spindle checkpoints = Checks that spindles are on kinetochores.
3) APC adenomatous polyposis coli = Protein that activates a transcription factor Myc, which allows transcription of a number of genes to progress from G1 to S. So this protein is needed to regulate cell cycle
4) p53 = Can detect DNA damage and inhibit cell cycle by blocking CDK2. Also causes apoptosis
5) Protein ataxia telangiectasia (ATM) = Also detects DNA damage and stops cell cycle.

Question 26

Can you describe cancers by their embryological origin

Answer 26

Carcinomas are derived from endoderm or ectoderm. 
While sarcomas are from mesoderm
Leukaemias are a class of sarcoma that grow as indivisual cells in the blood.

Question 27

What is southern blotting and how does it work

Answer 27

Used to detect the presence and amount of a particular sequence of DNA

Question 28

What is northern blotting, and how dows it work

Answer 28

Very similar as for southern blotting. Used to detect presence and amount of particular RNA

Question 29

What is western blotting and how does it work

Answer 29

Used to detect the presence and amount of a specific protein in a tissue sample.

Works by using gel electophoresis. Where proteins that are in a gel matrix then exposed to electrical current. The smaller proteins travel faster. You use immunoblotting against the particular protein you are interested in.

Question 30

What is Polymerase chain reaction and how does it work

Answer 30

Used to amplify a specific sequence of DNA or RNA. If RNA rather then DNA, then first you need to transcribe it into complementary cDNA by reverse transcriptase. Used to genetic testing, forensics and scientific research

Question 31

What is DNA Microrarrays and how does it work

Answer 31

This is a collection of thousands of DNA spots (short oligonucleotides) that are all around a solid surface. Used for simultaneous analysis of the expression of thousands of genes.

Question 32

What is bioinformatics and how does it work

Answer 32

Term use to describe the computer methods for storing, distributing and analysis a huge number of DNA sequences. SUch as Gene banks

Question 33

What is proteomics and how does it work

Answer 33

The large scale study of proteins, their structures, and their function