Lecture 8: Biological Membranes Flashcards Preview

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Flashcards in Lecture 8: Biological Membranes Deck (54):
1

Features: General structure

 

sheetlike structures - 2 molecules thick - that form closed boundaries between different compartments

2

Features: Makeup of membranes

 

- lipids and proteins

- mass ratio ranges from 1:4 and 4:1

- never any higher/lower than this ratio

- vary for different membranes

- some also contain carbohydrates that are linked to lipids and or proteins

3

Features: spontaneous activity

- hydrophilic and hydrophobic moieties

- spontaneously form closed bimolecular sheets in aqueous media

- barriers to the flow of polar molecules

4

Features: proteins

 

- embedded in the lipid bilayer

- mediate distinctive functions

- serve as pumps, channels, recepctors, transducers and enzymes

5

Features: Interactions of membranes

 

noncovalent interactions, act cooperatively

6

Features: Symmetry of membranes

 

- asymmetric

- two faces (leaflets, layers) of biological membranes have different lipid compositions

- individual peripheral membrane membrane proteins are only associated with one side of th emmebrane while integral membrane proteins have different domains on different sides of the membranes

7

Features: Fluidity

 

- fluid structures

- lipids diffuse rapidly in the phase of th emmebrane, as do proteins unless anchored

- do not ROTATE across the membrane, can be considered as an oriented 2D solution

 

saturated vs unsaturated fatty acids

more unsaturated keep mem more fluid (lower temps)

8

Features: Polarized

 

- electrically polarized

- inside is -60mv

- membrane potential a key role in transport, energy conversion, excitability

9

What are lipids?

- consists mostly of hydrocarbons

- serve as fuel molecules and energy stores

- signal molecules and messengers

- one of the two main components of membranes

10

Three major types of lipids

- phospholipids

- sphingolipids

- steroids

11

Glycerol structure

 

3 alcohol groups

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Sphingosine structure

 

sphingosine makes up backbone and tail

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13

Fatty acids

 

- feature of phospholipids and glycolipids

- various lengths and degree of unsaturation

- fatty acids in biological systems usually ocntain even number of carbon atoms (14-24)

- unsaturated have at least one DB in cis

- polyunsaturated are separated by at least 1 methylene group

14

Fatty acid numbering

- start at carboxyl terminus

- methyl at distal (far) end is thne w-carbon and double bond is represented by ►with superscript

 

Ex: nutritionists number from the omega/terminal

Omega 3-6-9 has DBs beginning on each of those carbons

 

chemists number in opposite direction

15

Linolenate

 

chemist: 9-12-15 (from carboxyl terminus)

nutritionist: 3-6-9 (from end)

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What affects the fluidity of fatty acids?

 

- decreasing chain length

17

Glycerophospholipids structure

 

Head group:

- choline

- phosphate

- glycerol

1 saturated tail

1 unsaturated tail

 

*ester bonds (from joining alcohol and carboxylic acid)

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18

Breakdown of glycerophospholipids via phospholipases

 

- produces a variety of signal molecules such as diacylglycerol and inositol phosphates (including inositol 1,4,5 trisP)

 

phospholipases A1 and A2

phospholipases C and D

19

phospholipasesd A1 and A2

 

cleave fatty acids from a glycerophospholipid, producing lysophospholipids

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C and D phospholipases

hydrolyze on either side of the phosphate in the polar head group

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21

Sphingolipids

1 fatty acid chain

 

ester bond vs amide bond

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22

ABO Blood type

 

- blood genes exist in more than 2 alleles

- three alleles for blood

- attach different carbohydrates to membrane components

- Ia and Ib both code glycotransferases with different substrate specificity

- I gene is nonfunctional

23

Ia allele

 

- adds a-N-acetylgalactosamine to D galactose end of an oligosaccharide side chain of sphingolipid (H antigen

- makes A antigen

24

Ib allele

- encodes glycosyltransferase that joins  a-D galactose to the a-D-galactose end of H antigen

- creates b antigen

25

Resultant blood types

A (only AA or AO)

B (only BB or BO)

O (ii) --> do not produce

AB (AB)

26

Sphingolipids and diseases

 

- defect of lysosomal enzymes involved in sphingolipid degradation results int he acucmulation of partial breakdown products (storage substances) causeing serious diseases

- dont properly degrade lipids

- BUT these diseases still result in 70-80% functionality. If the pathway was totally destroyed the person wouldnt be alive

27

Whata re steroids?

- family of organic compoudns whose multiple (usually 4) fused rings share carbons

- in most cases an -OH is attached to at least 1 ring

- part of membranes or function as hormones to carry messages

 

-

28

deficiency of 17b-hydroxysteroid dehydrogenase 3

 

- reduces production of testosterone and can result in dev of male pseudohermaphroditism

- male doesnt go through puberty completely

29

Amphipathic membranes

 

- polar, hydrophobic head and nonpolar, hydrophilic tail

30

Basic forms of membrane

- micelle

- bilayer

- vesicle

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micelle

- spherical structure with limited amphipathic molecules arranged with its hydrophobic regions in interior

32

bilayer

 

2D sheet with 2 lipid monolayers

33

vesicle

open bilayer is relatively unstable and can spontaneously self-associate into a hollow vesivle, closed bilayer or liposome, enclosing aqueous activity

34

steps of lipids to membrane

 

unfavorable (planar phospholipid bilayer with edges exposed to water)

 

favorable ( sealed compartment formed by phospholipid bilayer)

 

* no energy needed (favorable)

35

Disrtibution of lipids a membrane

 

- asymmetric

- different lipids and proteins can be concentrated differently on either side

36

Fluid mosaic model

 

biological membranes

- consist of lipid bilayer in which membrane proteins are embedded

- considered an oriented 2D liquid- in which lipids and proteins diffuse more or less freely within the plane

- contain some defined structures or domains (protein complexes, lipid rafts)

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Lipid rafts

 

groups of lipids linked to/associated with proteins

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38

Types of membrane proteins

 

peripheral

integral

39

peripheral proteins

 

membrane proteins that lack exposed hydrophobic groups and do not penetrate the bilayer

40

integral proteins

 

- membrane proteins are amphipathic - hydrophobic an dhydrophilic regions or domains

- some extend across the lipid bilayer since they have 1 or mroe transmembrane proteins

- some partially embedded

41

interactions of proteins in the membrane

 

- independednt and interact noncovalently

- some have fattya cids or other lipids groups covalently attached and are referred to as anchored

- membrane spanning structures including b-strands, a-helices

- sequences of 20 consecutive nonpolar amino acids suggests a membrane spannins a -helical region of a protein

42

a helix in membrane IDd by

- 20 consecutive nonpolar amino acids

43

Types of membrane proteins

 

1. single span a helix

2. multiple span a helix

3. multiple b-span (b barrel)

4. nonspannign a helix

5. fatty acyl or prenyl anchor

6. lipid anchor with oligosaccharaide linker

7. peripheral mebrane

 

44

6 major functions of membrane proteins

 

- transport

- enzymatic activity

- signal transduction

- cell-cell regognition

- intercellular

- attachment to cytoskeleton and extraellular matrix

45

How are double bonds made in hydrocarbons?

 

oxidation aka dehydrogenation

46

How many carbons must be in fatty acid chain to find DBs?

- at least 16

47

Allergic reactions

 

- venom has phospholipases

- they break down erythrocytes

- immune reaction also occurs in response to degradation products

 

antivenom deactivated phospholipases

48

phospholipase C products

 

diacylglycerol and inositol 1,4,5 trisphosphate

 

diacylglycerol: activation of protein kinases, phosph in signaling pathways

inositol: increases Cell Ca2+, binding and reg

49

Determining blood type

 

- agglutination --> molecules join/link together

 

- add antibodies to blood sample

- A blood produces anti B antibodies, reacts with anti A

- B produces antiA, reacts with anti B antibodies

- AB blood produces no antibodies, blood reacts with both anti a and B

- O produces all antibodies, doesnt react with anti A or anti B antibodies

50

Importance of cholesterol

- NEED for cellular membranes

- hydrophobic but must be transported through hydrophilic blood

- carried in bowl like structure

- too much can build up and cause heart disease or stroke (plaque)

51

steroids and gender determination

 

- activate hundreds of transcription factors

- can change complete expression patters

 

male vs female

52

where are lipids made?

-golgi apparatus

- "melt" into membranes

53

membrane protein complexes

 

- do not move, cannot free flow

- like cytochrome C

54

hydropathy index

certain types of proteins and aas more likely to be span membrane

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