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Biochem > Module 4 > Flashcards

Module 4 Flashcards

1
Q

Lipids are incorporated into . . .

A

triacylglycerols + waxes + phospholipids

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2
Q

Monounsaturated fatty acids are usually in the ___ config

A

CIS

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3
Q

Define fatty acids

A

carboxylic acids w a hydrocarbon chain b/w 4 to 36 carbons long

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4
Q

Are double bonds normally conjugated in unsat fatty acids?

A

NO

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5
Q

As the HC chain gets longer, the fatty acids melting point gets. . .

A

HIGHER
- sat fat acids can pack into stable aggregates
- nearly crystalline array
- stabilized by extensive hydrophobic interactions on the HC chain

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6
Q

Cis fatty acids pack less orderly due to the. . .

A

kink
- less thermal energy needed to disrupt disordered packing

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7
Q

How are trans fatty acids made?

A

partial dehydrogenation of unsaturated fatty acids

higher melting point

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8
Q

How to count when naming fatty acids?

A

start counting from carboxyl group when trying to work out where the bonds are

unless you’re talking about omega, start from other side

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9
Q

3 structural properties of triacylglycerols

A

1) composed of glycerol backbone

2) the 3 OH of glycerol provide the 3 sites for fatty acid linkage (ester linkages)

3) all are hydrophobic

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10
Q

3 functional features of triacylglycerols

A

1) when broken down into constituent fatty acids, can go onto oxidation to produce energy

2) provide stored energy + insulation

3) not hydrated (less weight) - so carry no water

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11
Q

Wat are the 2 types of phospholipids?

A
  • glycerophospholipids
  • sphingolipids
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12
Q

What is the most common glycerophospholipid?

A

phosphatidylcholine

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13
Q

What does the charge on each glycerophospholipid depend on?

A

the charge on each will depend on IDENTITY of head group (ranges from -4 to 0)

simplest example is phosphatidic acid, where X=H

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14
Q

What are some features of sphingolipids?

A

carbons 1, 2, & 3 of the sphingosine backbone can be considered equivalent to the 3-C glycerol, but in addition the sphingosine contributes 1 of the 2 tails

simplest example is CERAMIDE

sphingolipids don’t ALWAYS contain a phosphate group, but CAN also fall into a glycolipid grouping

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15
Q

What are some features of glycolipids?

A

contain mono or oligosaccharide units in their HEAD groups

are components of the outer membrane leaflet

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16
Q

What is lateral diffusion?

A
  • when the lipid moves from one end of a bilayer to another area in the same layer
  • FRAP can be used to demonstrate lateral diffusion
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17
Q

What is FRAP?

A
  • react cell w fluorescent probe to label lipids
  • view surface with fluorescence microscope
  • intense laser beam bleaches small area
  • with time, unbleached phospholipids diffuse into bleached region
  • measure rate of fluorescence return
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18
Q

Flip-flop transverse diffusion requires. . .

A

catalysis (enzyme) bc it is highly energetically unfavourable

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19
Q

3 types of transbilayer translocations

A

1) Flippase (out to in)

2) floppase (in to out)

3) scramblase

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20
Q

As temp increases in membrane, heat produces. . .

A

thermal motion of acyl side chains (from paracrystalline state / solid to fluid state)

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21
Q

What are membrane rafts?

A

slightly thicker, more ordered and harder to dissolve non-ionic detergents than the surrounding regions

allows for efficient signalling IN and OUTSIDE of cel

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22
Q

Properties of peripheral membrane proteins

A

associated w membranes by IONIC INTERACTIONS & H bonding with
1) polar head groups of lipids
2) integral membrane proteins

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23
Q

Properties of integral membrane proteins

A

associated w membranes by HYDROPHOBIC INTERACTIONS w:
1) acyl chains of membrane lipids
2) integral proteins are all oriented in same way within bilayer
3) protease sensitivity of protein from intact cells –> CHOPPING UP PROTEINS

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24
Q

How are peripheral membrane proteins experimentally released from biological membranes?

A

1) high salt
2) change in pH
3) chelating agent (binds metals more tightly)

  • all of these factors disrupt ionic interactions and separate proteins from the membranes
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25
Q

Why is a hydropathy plot useful?

A

helps us determine which proteins are transmembrane

helps us predict numbers of typical membrane helices

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26
Q

Can we predict which proteins are membrane proteins just based on their amino acid sequence?

A

i. Sequence will consist of hydrophobic amino acids
ii. Conformation will be an a-helix
iii. Span (segment of protein) equal to width of membrane

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27
Q

Provide an example of an passive transporter.

A

GLUT 1
- facilitates passage of glucose DOWN a concentration gradient
- glucose transporter exists in 2 conformations
- binding of glucose (from blood plasma) may induce a change from T1 to T2

28
Q

Provide an example of an active transporter.

A

P-type ATPases
- ATP powered pumps
- the hydrolysis of ATP to ADP produces energy which drives the conformational change that allows the molecules to be transported across the membrane
- phosphorylation also stabilises the conformation of that enzyme to release the molecules

29
Q

IN A HYDROPATHY PLOT, what is the charge of the HYDROPHOBIC region?

A

Hydrophobic = +
Hydrophilic = -

30
Q

How are integral membrane proteins released from membranes and studied?

A

released from membrane by reagents that disrupt hydrophobic interactions, e.g. detergents (such as SDS – sodium dodecyl sulphate)

i. They interact with membrane, specifically the hydrophobic regions
ii. They solubilize chunks of lipid into the solution
iii. Same thing happens with the protein

31
Q

What are monosaccharides?

A

aldehyde or ketones that have 2 or more hydroxyl (OH) groups (CH2O)n

32
Q

What’s the difference between a ketose and aldose?

A

ketose contains ketones, aldose contains aldehyde

in aldehydes, the presence of a tetrahedral carbon w. 4 dif substituents gives rise to chirality

33
Q

Fructose is a _____ while glucose and ribose are _____

A

ketose

aldoses

34
Q

Most natural sugars belong to . . .

A

the D series; they’re all structurally related to D-glyceraldegtde

  • OH projects to the RIGHT in D when CHO is on top
  • of the asymmetric carbon furthest away from the aldehyde group
    (aldehyde group carbon is carbon-1)
35
Q

What is special about Fischer projections?

A

provide a clear and simple view of the stereochemistry at each carbon centre

horizontal lines = out of plance

36
Q

Monosaccharides have. . .

A

2 or more carbons

37
Q

How many chiral centers do aldohexoses have?

A

4

therefore 16 steroisomers

38
Q

How do D-glucose and D-mannose differ?

A

only in config at C-2

39
Q

What are epimers?

A

sugars that differ only in the config around one carbon atom

40
Q

How does the pyranose ring form?

A

Pyranose is a chemical structure that is comprised of a ring. The ring is made up of six members that contain 5 Carbon and 1 Oxygen atom.

  • the OH on C-5 attacks the carbonyl of the aldehyde group & form a HEMIACETYL linkage
  • when the system cyclizes, a new tetrahedral carbon forms with an OH on it

LURD

41
Q

What are 2 modifications of monosaccharides?

A

GalNAc and GlcNAc

42
Q

How are disaccharides defined?

A

by the MONOSACCHARIDES and NATURE OF LINKAGES

43
Q

What are polysaccharides?

A
  • large polymeric structures
  • unbranched homopolysaccharides include structural elements on plant cell walls (cellulose) & chitin
  • storage fuels include the branched starch (plants) & glycogen (animals)
44
Q

Aldehydes are capable of. . .

A

REDUCING other groups by becoming itself oxidized to a carboxylic acid

45
Q

How can sugar concentrations be determined by measuring Cu2O?

A
  • as increase in concentration of glucose in sample, there’s an increase in conversion of Cu2+ to Cu+
  • so, the colour changes from blue to red
46
Q

Which sugar in the chain can open up?

A

ONLY 1, that is the reducing sugar (usually shown to the right)

47
Q

What are some features of chitin?

A
  • is a linear homopolymer of N-acetylglucosamine residues
  • similar to cellulose, only different is the presence of an acetylated amino group at C-2
48
Q

There is less H bonding in. . .

A

glycogen and starch

have an open helix structure

49
Q

Why are glycoproteins important?

A

carbohydrate groups are COVALENTLY attached to many proteins called GLYCOPROTEINS

cell-cell adhesion / recognition

50
Q

What are the 2 ways in which carbohydrates can be linked to proteins?

A

1) via the AMIDE side chain of asparagine (GlcNAc - N- Asn)

2) via serine or threonine residues at hydroxyl side chains (O-glycans)
GalNAc- O- Ser

51
Q

What do glycosyltransferases do?

A

catalyzes the transfer of sugar (responsible for oligosaccharide assembly)

the hydrolysis of the (nucleotide-monosaccharide) bond with drive the reaction

monosaccharide is transferred from nucleotide sugar to non-reducing end of carbohydrate acceptor

52
Q

ABO blood group antigens are . . .

A

GLYCOSPHINGOLIPIDS

  • A & B blood group antigens differ from O antigen by one extra monosaccharide

carbohydrates are attached to glycoproteins (& glycolipids) on surfaces of red blood cells

53
Q

A vs B antigen

A

A has GalNAc

B has Gal

54
Q

ABO blood group genes encode a . . .

A

glycosyltransferase (enzyme)

eg. GalNAc transferase for A

55
Q

O allele product is a . ..

A

DEAD enzyme (no active transferase)

56
Q

How is B allele diff to A allele?

A

allele has some amino acid substitutions; it cannot bind GalNAc, only Gal
the O allel ehas a premature STOP codon so we can only translate 1 to 118 amino acids

57
Q

Are there antibodies to the O antigens?

A

NOO

58
Q

What happens when antibodies come into contact with antigens?

A

antibodies will cross link the ‘foreign’ red blood cells (AGGLUTINATION)

incompatibility leads to HEMOLYSIS and can be deadly

59
Q

What is the universal donor?

A

O blood

60
Q

What are some features of the GLUT transporters?

A

composed of 12 alpha helices containing amino acids

  • model with 4 amphipathic helices (1, 4, 7, and 10)
  • central polar region allowing the glucose interactions

heptad is reversed, we now have hydrophilic residues at a and d

both N ter and C ter inside

61
Q

What are lectins?

A

broad family of proteins which recognize carbohydrates

one large class of them known as C type lectins

62
Q

How do C-type lectins recognize carbohydrates?

A
  • C-type for calcium binding
  • calcium acts as a bridge between the protein & the sugar through direct interaction with sugar hydroxyl groups
63
Q

What are some features of C type lectins?

A
  • calcium forms an octahedral coordination complex
  • different C-type lectins have diff carbohydrate binding specificities
  • changes in residues that interact with the sugar alter the carbohydrate binding specificity of the lectin
64
Q

What are selectins?

A
  • involved in cell-cell adhesion
  • class of C-type lectins
  • bind white blood cells to sites of injury & allow movement of cells from blood stream to site of infection
65
Q

How do leukocytes interact with P-selectins?

A
  • site of infection
  • causes the expression / activation of P selectins around site of infection
  • leukocyte binds to selectin via carbohydrates on gylcoproteins
  • moves down from one selectin to the next until is reaches site of infection
  • can move through endothelium to attack the virus / bacterium etc.
66
Q

How do sugars on cell surface interact with the influenza virus & how has that been used to interact with a drug?

A
  • infected host cell gets taken over by influenaz virus
  • synthesizing more influenza virus that will bud off and infect other cells
  • virion is the new virus
  • it is still associated on the surface of the original cell via a receptor containing sialic acid
  • hemagglutinin is what binds to sialic acid
  • it can use neuraminidase on its surface (of virion) to separate from the host cell
  • neuraminidase inhibitors (relenza) binds to all the copies of neuraminidase on the surface of virion and stops it being able to cleave off the host cell - virus remains stuck
  • it doesn’t STOP the initial infection; it simply stalls it

Biochem (9 decks)

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