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Human Sciences > Biological Membranes > Flashcards

Biological Membranes Flashcards

1
Q

Why do membranes form bilayers?

A

Phospholipids are amphipathic

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2
Q

What are the four membrane protein types and their examples?

A
  • Tansporters- Na/K pump
  • Linkers- cytoskeleton to membrane
  • Receptors- for GFs
  • Enzymes- adenyl cyclase- catalyses production of cAMP
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3
Q

What are the differences between archaea and eubacteria/eukaryota phospholipids?

A
  • A= branched isoprene chains, E= unbranched fatty acids
  • A= ether linkage (C-O), E= Ester linkage (O=C-O)
  • A= L-glycerol, E= D-glycerol
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4
Q

What are retinal rod cells made up of?

A

Discs

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5
Q

How can rhodopsin content in rod cell discs be measured and how much of the membrane protein does it make up?

A
  • Low angle X-ray diffraction of isolated discs

* 80% of disc membrane protein

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6
Q

Why is the diffraction pattern of rhodopsin evidence for the fluid mosaic model?

A

The pattern is reinforced by the binding of antibodies to the cell membrane.
This pattern changes with temperature- incompatible with planar crystalline lattice structure

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7
Q

How do somatic cell fusion experiments provide evidence for fluid mosaic model?

A
  • Mouse and human cell fused- mix of antibodies

* Incubated to 40*c -> proteins have diffused as membrane is fluid- no longer two clear halves

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8
Q

How do FRAP experiments support the fluid mosaic model?

A

Fluorescence recovery after photobleaching:
• Certain membrane components marked by fluorescent labels
• Defined membrane areas bleached by laser
• Area will be depopulated with fluorescent components as they’re free to move

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9
Q

What’s the width of the lipid bilayer?

A

5nm

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10
Q

What is a nascent polypeptide?

A

Polypeptide still attached to ribosome synthesising it

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11
Q

What happens to cytosolic nascent polypeptides?

A
  • Ribosome associates with ER membrane, cotranslational import into lumen, then transport to destination
  • OR remains in cytosol and so does protein product. Post-translational import into organelles can then occur
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12
Q

What is the signal hypothesis?

A
  1. First amino acids synthesised are a signal peptide
  2. Recognises by receptor protein with associated pore on ER membrane
  3. Signal peptide may later be cleaved
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13
Q

Outline cell fractionation

A
  1. Homogenisation- no outer membrane

2. Centrifugation- separates organelles

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14
Q

What do scintillation counters do?

A

Detect newly synthesised proteins as they are radioactive ^3H

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15
Q

What is a pulse chase experiment?

A

Exposing cells to a labelled compound and and then to an unlabelled form
• Position of ^3H labelled protein/amino acid tracked by cell fractionation/EM autoradiography

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16
Q

What does the Golgi apparatus do?

A
  • Receives entire output of newly synthesised proteins and lipids from ER. processes in stacked cisternae and distributes inside/outside cell
  • modification of polypeptides and membrane lipids
  • glycolisation
17
Q

Which is the trans face of the Golgi?

A

Exit side of the organelle

18
Q

Which is the Cis-face of the Golgi?

A

Recruits from RER

19
Q

What do scaffold proteins do in the Golgi?

A

Maintain the polarised stacks of cisternae

20
Q

What is constitutive exocytosis?

A

Mucus and glycoproteins of extracellular matrix

21
Q

What is regulated exocytosis?

A
  • Neurotransmitters

* Zymogen granules (storage organelles for digestive enzymes)

22
Q

What are the requirements of a good experimental cell system?

A
  • Grow in lab under simple conditions
  • Grow on agar for single cell manipulation
  • Genetics- ready isolation of mutants
  • Express asymmetry of from- polarised

Eg budding yeast

23
Q

What do SNARE proteins do?

A

Matching pairs on vesicles and targets

v-SNAREs and t-SNAREs

24
Q

How is directional flow of vesicles ensured?

A

Ran proteins and NTP hydrolysis- prevents anything other than correct sequence of events

25
Q

What is the plasmalemma?

A

The plasma membrane that bounds a cell

Human Sciences (8 decks)

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