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AH biology > Unit 1 KA 4&5 > Flashcards

Unit 1 KA 4&5 Flashcards

1
Q

Multicellular organisms signal between cells using what?

A

extracellular signalling molecules

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2
Q

Give three examples of extracellular signalling molecules

A

steroid hormones, peptide hormones and neurotransmitters.

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3
Q

receptor molecules of target cells are…

A

proteins with a binding site for a specific signal molecule

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4
Q

What does binding do?

A

Changes the receptor’s conformation which initiates a response in the cell.

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5
Q

Different cell types produce…

A

specific signals that can only be detected and responded to by cells with the specific receptor.

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6
Q

Why may signal molecules have different effects on different target cells?

A

differences in the intracellular signalling molecules and the pathways that are involved.

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7
Q

In multicellular organisms, certain cells may show a ________ response to an extracellular signal

A

tissue specific response

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8
Q

T or F - Hydrophillic signalling molecules bind to intracellular receptors and diffuse directly through phospholipid membranes

A

False - hydrophobic signalling molecules.

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9
Q

What are the receptors for hydrophobic signalling molecules called?

A

transcription factors

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10
Q

What is a transcription factor?

A

A protein that when bound to DNA can either stimulate or inhibit initiation of transcription.

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11
Q

True or False - The steroid hormones estrogen and testosterone are examples of hydrophobic signalling molecules

A

True

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12
Q

Steroid hormones bind to specific receptors where?

A

In the cytosol or nucleus

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13
Q

The hormone receptor complex moves to the nucleus where it does what?

A

Binds to specific sites on DNA and affects gene expression.

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14
Q

The hormone receptor complex binds to specific sites that are called…

A

HREs

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15
Q

Binding of the hormone recpetor complex at a HRE does what?

A

Influences the rate of transcription with each steroid hormone affecting the expression of multiple different genes.

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16
Q

Where do hydrophillic signalling molecules bind?

A

The transmembrane receptors and they don’t enter the cytosol

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17
Q

Give two examples of hydrophillic extracellular signalling molecules?

A

peptide hormones and neurotransmitters

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18
Q

What happens when transmembrane receptors bind to the extracellular face?

A

The transmembrane receptors change conformation; the signal molecule does
not enter the cell, but the signal is transduced
across the plasma membrane

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19
Q

Transmembrane receptors act as signal transducters by doing what?

A

converting the extracellular
ligand-binding event into intracellular signals,
which alters the behaviour of the cell.

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20
Q

Transduced hydrophobic signals often involve what?

A

G proteins or phosphorylation cascades by kinase enzymes.

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21
Q

What is the function of a G protein?

A

G-proteins relay signals from activated receptors (receptors that have bound a
signalling molecule) to target proteins such as enzymes and ion channels.

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22
Q

How many intracellular signalling pathways do phosphorylation cascades allow to be affected?

A

More than one

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23
Q

T or F - Phosphorylation cascades involve just 1 event.

A

F - They involve a series of events with one kinase activating the next in the sequence and so on. They can result in the phosphorylation of many proteins as a result of the original signalling event.

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24
Q

Binding of the peptide hormone insulin results in…?

A

a conformational change that triggers
phosphorylation of the receptor. This starts a
phosphorylation cascade inside the cell,
which eventually leads to GLUT4-containing
vesicles being transported to the cell
membrane.

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25
Q

What causes type 1 diabetes?

A

An autoimmune response which causes the body to be unable to produce insulin.

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26
Q

What causes type 2 diabetes?

A

Loss of receptor function which causes the body to become insulin resistant.

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27
Q

Doing what can help improve the symptoms of type 2 diabtes?

A

Exercise; it triggers the recruitment of GLUT-4 molecules that improve glucose uptake of fat and muscle cells in the body.

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28
Q

Resting potential

A

A state where there is no net flow of ions across the cell membrane.

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29
Q

The transmission of a nerve impulse requires…

A

changes in the membrane potential of the neuron’s plasma membrane.

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30
Q

Action potential

A

A wave of electrical excitation along a neuron’s plasma membrane.

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31
Q

Give the steps of nerve transmission.

A

1) A neurotransmitter binds to a receptor at a synapse and initiates a response in the cell.
2) Ligand gated sodium channels open and cell’s action potential begins to rise.
3) Once action potential reaches a certain threshold, voltage gated sodium channels open and sodium ions rapidly diffuse into the cell.
4) Once the cell has depolarised and now has the voltage of 30mV, the voltage gated sodium channels deactivate and voltage gated potassium channels open.
5) Potassium ions rush out the cell and it returns back to its resting potential.
6) Hyperpolarisation happens and the sodium potassium pump transports excess concentrations of ions in and out the cell.

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32
Q

Retina

A

The area in the eye which detects light and contains 2 types of photoreceptor cells - rods and cones.

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33
Q

Rod cells

A

They function in dim light and do not allow colour perception

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34
Q

Cone cells

A

They only function in bright light and allow colour perception

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35
Q

In animals, the light sensitive molecule retinal combines with what?

A

The membrane protein, opsin, which makes rhodopsin.

36
Q

What happens when retinal absorbs a photon of light?

A

Rhodopsin changes conformation and becomes photoexcited rhodopsin.

37
Q

What amplifies the the signal that allows rhodopsin to change conformation?

A

A cascade of proteins.

38
Q

Photoexcited rhodopsin activates a G protein called what?

A

Transducin

39
Q

What does transducin activate?

A

the enzyme PDE

40
Q

A single molecule of photoexcited rhodopsin can activate how many molecules of G protein?

A

100s. 1 G protein molecule however only activates 1 molecule of PDE

41
Q

PDE catalyses the hydrolysis of a molecule called…

A

cGMP

42
Q

Each active PDE molecule can break down how many cGMP molecules per second?

A

Thousands

43
Q

The reduction in cGMP concentration as a result of its hydrolysis can affect what?

A

function of ion channels in the membrane of rod cells

44
Q

The hydrolysis of cGMP results in closure of ion channels in rod cell membranes which triggers what?

A

nerve impulses in the retinal neurons

45
Q

A _____ degree of amplification results in rod cells being able to respond to low light intensities

A

very high degree of amplification

46
Q

In cones, different forms of opsin combine with retinal to give different photoreceptors each with a maximal sensitivity to what?

A

Different wavelengths of light: red, green, blue or UV

46
Q

What does the cytoskeleton give to cells?

A

mechanical support and shape

47
Q

The cytoskeleton consists of different protein structures including ______ which are all found in eukaryotic cells

A

microtubules

48
Q

microtubule

A

a hollow cylinder composed of the protein tubulin. They radiate from the microtubule organising centre or centrosome.

49
Q

What do microtubules control?

A

The movememnt of membrane bound organelles and chromosomes

50
Q

What does cell division require?

A

remodelling of the cytoskeleton

51
Q

Formation and breakdown of microtubules involves what happening?

A

polymerisation and depolymerisation of tubulin

52
Q

What do microtubules form?

A

The spindle fibres that are active during cell division

53
Q

Name the two main stages of the cell cycle

A

Interphase and Mitotic phase

54
Q

What is involved in interphase?

A

Growth and DNA synthesis - its three phases are G1, S, and G2 phase

55
Q

What happens during each stage of interphase?

A

In G1 and G2 phases, the cell grows and in S phase, DNA replication happens

56
Q

Name the 4 stages of the mitotic phase.

A

Metaphase, Anaphase, Telophase, Cytokinesis

57
Q

What happens during mitosis?

A

The chromosomal material is separated by the spindle microtubules

58
Q

What happens in cytokinesis?

A

The cytoplasm separates into 2 daughter cells.

59
Q

What happens during prophase?

A

DNA condenses into chromosomes each consisting of two sister chromatids. Nuclear membrane breaks down; spindle microtubules extend from the MTOC
by polymerisation and attach to chromosomes via their kinetochores in the
centromere region.

60
Q

What happens during metaphase?

A

Chromosomes line up at the metaphase plate

61
Q

What happens during anaphase?

A

as spindle microtubules shorten
by depolymerisation, sister chromatids are
separated, and the chromosomes are pulled
to opposite poles.

62
Q

What happens during telophase?

A

the chromosomes decondense and nuclear membranes are formed around
them.

63
Q

Progression through the cell cycle is controlled by what?

A

checkpoints

64
Q

Checkpoints

A

mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met.

65
Q

During the cell cyle, cyclin proteins accumulate. What are they responsible for doing?

A

regulating the cell cycle

66
Q

During the cell cycle, what do cyclin proteins combine with and activate?

A

CDKs.

67
Q

What do CDKs do?

A

phosphorylate proteins that
regulate progression through the cycle. If
sufficient phosphorylation is reached,
progression occurs.

68
Q

At the G1 checkpoint, retinoblastoma protein does what?

A

acts as a tumour suppressor by
inhibiting the transcription of genes that code
for proteins needed for DNA replication

69
Q

Phosphorylation by what inhibits the retinoblastoma protein?

A

G1 cyclin-CDK

70
Q

By inhibiting retinoblastoma, G1 cyclin-CDK allows for what to happen?

A

transcription of the genes that code for proteins needed for DNA replication.
Cells progress from G1 to S phase.

71
Q

What is assessed at the G2 checkpoint?

A

The success of DNA replication and any damage done to DNA

72
Q

DNA damage stimulates what?

A

the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death

73
Q

A metaphase checkpoint controls what?

A

progression from metaphase to anaphase

74
Q

At the metaphase checkpoint, progression is halted until what happens?

A

The chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules

75
Q

An uncontrolled reduction in the rate of the cell could result in what?

A

degenerative disease e.g alzheimers

76
Q

An uncontrolled increase in the rate of the cell cycle could result in what?

A

tumour formation

77
Q

What is a proto-oncogene?

A

A normal gene that is usally involved in controlling cell growth/division. It can mutate to form a tumour-promoting oncogene.

78
Q

Apoptosis

A

Programmed cell death which is triggered by cell death signals that can be either internal or internal

79
Q

Give an example of an external death signal

A

Production of death signal molecules from lymphocites

80
Q

Give an example of an internal death signal

A

DNA damage

81
Q

External death signals do what to trigger a protein cascade in the cytoplasm?

A

bind to a surface receptor protein

82
Q

An internal death signal resulting from DNA damage causes what?

A

Activation of p-53 tumour suppressor protein

83
Q

Both types of death signal result in the activation of what?

A

caspases (types of protease enzyme) that cause the destruction of the cell

84
Q

Apoptosis is essential during development of an organism because…

A

it removes cells no longer needed by the organism as development progresses or during metomorphosis

85
Q

Cells may initiate apoptosis in the absence of what?

A

growth factors

AH biology (2 decks)

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