Unit 1 - Test 2

Question 1

what do multicellular organisms use to signal between each other?

Answer 1

extra-cellular molecules

Question 2

examples of extra-cellular signalling molecules

Answer 2

hormones (steroid + peptide), neurotransmitters

Question 3

what are receptor molecules on target cells?

Answer 3

proteins with a binding site for a specific signal molecule.
binding changes the conformation of the receptor, which initiates a response within the cell

Question 4

variation in responses?

Answer 4

different cell types may show a specific and different tissue response to the same signal

Question 5

steriod hormones

Answer 5

• are lipophilic so can freely diffude across the membrane
• they bind to nucleus or cytoplasm of target cell
• examples include oestrogen and testosterone
• hormone-receptor complex moves to the nucleus where it bonds to specific sites on DNA and affects gene expression
• specific DNA sites are called hormone response elements (HREs), binding here influences the rate of transcription

Question 6

peptide hormones

Answer 6

• they are lipophobic (fat-hating) so cannot freely diffuse across membrane
• bind to specific receptors on the surface of target cells

Question 7

neurotransmitters

Answer 7

• chemical messengers
• transmit messages over much shorter distances than hormones
• carry messages across the synapse

Question 8

hydrophobic signalling molecules

Answer 8

• able to directly diffuse through the phospholipid bilayer
• once inside cell they bind to intracellular receptors
• these intracellular receptors are 𝐭𝐫𝐚𝐧𝐬𝐜𝐫𝐢𝐩𝐭𝐢𝐨𝐧 𝐟𝐚𝐜𝐭𝐨𝐫𝐬

Question 9

hydrophilic signalling molecules

Answer 9

• bind to transmembrane receptors
• conformational change of receptor after ligand binds
  *signal molecule is tranduced across the plasma membrane; transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into specific intracellular signals, altering the behaviour of the cell

Question 10

transduction

Answer 10

• involves a series of reactions that occur inside the cell through a signal transduction pathway
• transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes

Question 11

G- proteins

Answer 11

• relay signals from activated receptors to target proteins (e.g. enzymes and ion channels)
• they are a family of proteins that act as molecular switches inside cells, involved in transmitting stimul from outside to the interior of the cell

Question 12

transduction by phosphorylation cascades

Answer 12

• involves a series of events with one kinase activating the next in the sequence, and so on
• can result in the phosphorylation of many proteins

Question 13

GLUT4 proteins

Answer 13

• glucose transporters
• binding of insulin to GLUT4 receptor triggers phosphorylation of this receptor, starting a 𝗰𝗮𝘀𝗰𝗮𝗱𝗲 within the cell
• eventually leads to GLUT4-containing vesicles being transported to the membrane to increase GLUT4 activity in the membrane

Question 14

what is a transcription factor?

Answer 14

a protein, when bound to DNA, will either activate or inhibit transcription

Question 15

what is resting membrane potential?

Answer 15

a state where there are no net flow of ions across the membrane

Question 16

what does the transmission of a nerve impulse require?

Answer 16

a change in the membrane potential of a neurons plasma membrane

Question 17

what is an action potential?

Answer 17

an action potential is a wave of electrical excitation along a neurons plasma membrane

Question 18

what does binding of a neurotransmitter to its receptor trigger?

Answer 18

the opening of ligand-gated ion channels at 𝘀𝘆𝗻𝗮𝗽𝘀𝗲.