cell communication

Question 1

what is the role of protein kinases and protein phosphates in signal transduction?

Answer 1

protein kinases: transfer phosphates from ATP to protein in a process called phosphorylation, turning on most proteins
protein phosphatases: remove phosphates from proteins in a process called dephosphorylation, which usually inactivates the protein

Question 2

examples of signal transduction pathways stimulating a cytoplasmic response?

Answer 2

turning enzymes on/off, opening/closing channels

Question 3

examples of signal transduction pathways stimulating a nuclear response?

Answer 3

turning gene transcription on/off, regulating synthesis of enzymes or other proteins

Question 4

what are some examples of specificity of cell signalling?

Answer 4

• different cells produce different proteins
• different proteins allow different cells to detect and respond to different signals
• also means that the same signal can lead to different responses in different cell types (eg. adrenaline can increase heart rate, open airways, increase blood flow in some vessels, decrease blood flow in other vessels)

Question 5

why is signal termination important in cell signalling?

Answer 5

• allows cell to receive new signals, prevents excessive responses which can lead to disease states (eg. excessive stimulation of growth and cell division leads to cancer)

Question 6

when does signal termination happen?

Answer 6

• when the signal molecule leaves the receptor and the receptor reverts to its inactive state
• it is now ready for another incoming signal

Question 7

what is apoptosis?

Answer 7

• programmed or controlled cell death that infected or damaged cells undergo

Question 8

how does apoptosis work?

Answer 8

the cell digests its cellular components by packaging them into vesicles, which are removed by white blood cells without inflammation. this prevents enzymes from leaking out of dying cells and damaging neighbouring cells.

Question 9

purpose of apoptosis?

Answer 9

maintain healthy tissue, development and growth, immune system regulation.

Question 9

functions of cell wall?

Answer 9

• protects plant cell
• maintains cell shape
• prevents excessive uptake of water

Question 10

what are the layers of a cell wall and their features?

Answer 10

• primary cell wall (relatively thin and flexible)
• middle lamella (between primary walls, glues adjacent cells together)
• secondary wall (woody plants. between plasma membrane and primary cell wall, very strong)

Question 11

what is the plasmodesmata? function?

Answer 11

• channels between adjacent plant cells that allows the cells to communicate.
• allows passage of water, small solutes, and sometimes proteins and RNA between cells.

Question 12

what makes up the ECM?

Answer 12

proteins, protein fibers, glycoproetins

Question 13

what are the functions of the ECM?

Answer 13

support, adhesion, movement, regulation

Question 14

describe tight junctions

Answer 14

• membrane proteins fuse adjacent cell membranes together (like layers of quilt stitched together)
• prevents fluid from leaking between cells
• eg. prevents stomach acid from reaching tissues

Question 15

describe desmosomes

Answer 15

• integral proteins reinforced by cytoskeleton
• strong connection resists stretching, twisting
• eg. skin held together in strong sheets

Question 16

describe gap juntions

Answer 16

• channel proteins called connexins connect cells like a grommet
• allow exchange of small molecules and ions
• allows for communication between cells

Question 17

describe local signalling between two cells in contact

Answer 17

1. occurs directly between two adjacent cells by passing signalling substances through cell junctions (e.g. coordination of cardiac muscle contraction)
2. cell-cell recognition, which is contact between integrins/cell recognition proteins.

Question 18

describe local signalling across short distances (2 types)

Answer 18

• occurs between cells via local regulators (chemical messengers)
  1. paracrine signalling
  2. synaptic signalling

Question 19

what are the chemicals involved in long-distance signalling?

Answer 19

hormones

Question 20

what is long-distance signalling called in animals?

Answer 20

endocrine signalling

Question 21

what happens at the reception stage of cell signalling?

Answer 21

• the ligand binds with the receptor (cell surface or inside the cell)
• receptor activates relay molecules

Question 22

what happens at the transduction stage of cell signalling

Answer 22

• relay molecules connect signal to inner cell
• amplification of the signal
• secondary messengers involved (cAMP, IP3, calcium ions)
• protein kinases transfer phosphate groups from ATP to proteins (phosphorylation)
• protein phosphatases remove phosphates (dephosphorylation)

Question 23

what happens at the cellular response stage

Answer 23

• specific events turned on or off (gene transcription)
• ion channels opened or closed
• enzymes activated or deactivated

Question 23

List the two general locations a receptor might be located (what properties will the ligand have to bind to
each?)

Answer 23

• receptor could be on/in cell membrane or in cytoplasm/nucleus.
• ligand must be lipid-soluble to be able to enter cell and bind to receptors inside
• water-soluble ligands cannot enter, therefore bind with membrane protein receptors

Question 24

Define second messenger and describe two different types

Answer 24

=small non-protein, water-soluble molecules or ions.
two types: cAMP (cyclic), calcium ions