Multicellularity

Question 1

How does cAMP affect Dictyostelium discoideum?

Answer 1

Under adverse conditions, it goes from unicellular to multicellular. This is so they share nutrients and move in a migrating slug morphology to find nutrients.

Question 2

How does Dictyostelium discoideum migrating slug react to not finding food?

Answer 2

It forms a fruiting body which releases stress resistant spores which are released and can hopefully find food.

Question 3

What percentage of genes are expressed in only one type of cell?

Answer 3

15-20%

Question 4

What is the importance of signalling in multicellular organisms?

Answer 4

Cooperation so that the correct function takes place and prevent uncontrolled proliferation. Respond to extracellular stimuli

Question 5

What types of tissue are there? (7)

Answer 5

Epithelial
Connective
Muscle
Cardiac
Smooth
Skeletal
Nervous

Question 6

Which type of tissue has the least signalling?

Answer 6

Connective

Question 7

What are the three main types of plant tissue?

Answer 7

Dermal
Ground
Vascular

Question 8

Name the 5 stages of cell-cell communication

Answer 8

1. Synthesis of signalling molecule
2. Release of signal
3. Detection by receptor protein
4. Change to cellular behaviour
5. Removal of signal to terminate cellular response

Question 9

What makes a good signal?

Answer 9

Be released in appropriate quantities to only be detected by correct receptors.
Small enough to travel easily
Synthesised, altered or released quickly
Degraded or resequestered quickly
Appropriate binding affinity

Question 10

Why are lipid rafts important in signalling?

Answer 10

They allow spatial organisation of membrane proteins. The lipid micro-environments favour specific protein interactions and can activate signalling cascades.

Question 11

How can signalling molecules be transmitted through plasma membranes?

Answer 11

Channels/pores
Gap junctions
Connexin proteins which form tubes between plasma membranes
Plasmodesmata in plants which are conjoined membranes.

Question 12

What is endocrine signalling?

Answer 12

Signalling over a long distance, e.g hormones

Question 13

What is paracrine/autocrine signalling?

Answer 13

Local mediators, e.g growth factors, neurotransmitters, cytokines

Question 14

What is juxtacrine signalling?

Answer 14

Plasma membrane attached signals which use contact to signal. E.g delta/Notch

Question 15

Describe the nAchR

Answer 15

Pentameric
Each subunit spans the membrane 4 times. Asp and Glu residues to attract Na+

Question 16

Describe a multi-subunit ion channel Ach receptor

Answer 16

Pentameric
Ligand binding at two sites next to α-subunits causes conformational change. Opens voltage gated Ca2+ ion channels to further spread depolarisation.
T-tubules allow current to penetrate the cell and activate ryanodine receptors to release Ca2+

Question 17

How does skeletal muscle contraction happen?

Answer 17

Calcium binds troponin on actin to cause a conformational change in tropomyosin. This reveals myosin head binding sites. Myosin binds to actin and bends, inducing skeletal muscle contraction.
Myosin is reset by ATP hydrolysis

Question 18

How do voltage gated ion channels work?

Answer 18

When depolarised, positively charged voltage sensing helixes move towards the extracellular surface, letting Ca2+ through

Question 19

What subfamilies are there of the single pass receptor family?

Answer 19

Non-catalytic- cytokine receptors interact with enzymes
Catalytic- TGFβ, RTK or guanylate cyclase receptors.

Question 20

What are the substrates of eukaryotic kinases?

Answer 20

Histones
Receptors
Microtubules
Signalling molecules
Other kinases
Enzymes
Transcription factors

Question 21

What sorts of control are cytokines important for?

Answer 21

Prolactins- stimulate milk production
Interferons- Makes cells more resistant to virus infections.
Interleukins- important for T-cell activation
Erythropoetin- increases production of red blood cell precursors.

Question 22

Describe cytokine receptors

Answer 22

TM helix
Extracellular domain
Brings JAKs and receptors close enough to phosphorylate each other on activation lip upon ligand binding.

Question 23

What is STAT?

Answer 23

Transcription factor that binds phosphotyrosine residues via SH2 domain
Phosphorylated STAT dimerises, moves into the nucleus and activates genes to prevent blood cells breaking down