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BDS1 > Proteins, polysaccharides and lipids > Flashcards

Proteins, polysaccharides and lipids Flashcards

1
Q

What are the two structures found in the secondary structure of proteins?

A

a-helix and B-pleated sheet

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2
Q

Description of a-helix

A

A rod-like, right handed coil with 3.6 residues per turn.

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3
Q

How to a-helices form?

A

Hydrogen bonds between the CO of one amino acid and the NH of an amino acid 4 residues ahead

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4
Q

What proteins contain a-helices?

A

Strong, extensible proteins e.g. Hb, myoglobin, keratins, fibrins, myosin

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5
Q

Description of B-pleated sheets

A

Made of several zig-zag polypeptide chains that run either in parallel or antiparallel alongside each other. The CO and NH groups align with hydrogen bonding forming between them.

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6
Q

What proteins contain B-pleated sheets?

A

Proteins that require flexibility e.g. silk fibroin has the anti-parallel arrangement

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7
Q

Which is the only protein containing a triple helix?

A

Collagen

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8
Q

What is the term used to describe the three chains winding around each other in collagen (rope-like)?

A

Tropocollagen

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9
Q

How many amino acids are approximately found in one polypeptide chain of collagen?

A

~1000 aa per chain therefore about 3000 aa in one collagen molecule

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10
Q

Where do hydrogen bonds exist in collagen?

A

There are no H bonds within each chain, only between chains. H bonds between Hydroxyproline and Hydroxylysine residues hold the three strands together.

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11
Q

What is the repeating structure in collagen polypeptide chains?

A

X-Pro-Gly or X-Hyp-Gly

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12
Q

Where do covalent bonds exist in collagen?

A

Between Lys and His to form inter and intra-molecular cross-links

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13
Q

Which position does Glycine take in collagen?

A

Small Glycine residue sits inside the helix while the bulky R groups either side project outwards.

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14
Q

What are the features of fibrous proteins?

A

Insoluble, metabolically unreactive, rope-like, strong

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15
Q

What is the function of fibrous proteins?

A

Structural function

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16
Q

Examples of fibrous proteins

A

Collagen, keratin, fibrin, elastin, myosin

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17
Q

What are the features of globular proteins?

A

Spherical as the backbone folds in on itself. Water-soluble and compact.

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18
Q

What level of protein structure do globular proteins typically exhibit?

A

Tertiary (e.g. myoglobin and actin) and Quaternary (e.g. Hb)

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19
Q

Function of myoglobin

A

oxygen storage in muscle

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20
Q

Structure of myoglobin

A

Globular protein with a tertiary structure (single chain 153aa). 8 helical regions joined by random coiling which produces major directional changes. No B-pleated sheets

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21
Q

Structure of the interior of myoglobin

A

Contains entirely non-polar residues except 2 polar His residues which allow the attachment of haem group

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22
Q

Where is the prosthetic haem group found in myoglobin?

A

In the hydrophobic pocket where it is held in position by hydrophobic interactions between the haem porphyrin ring and non-polar side chains of amino acids

23
Q

What would happen if the haem group in myoglobin was absent?

A

Myoglobin would become an apoprotein - not as tightly folded

24
Q

What level of protein structure does Haemoglobin exhibit?

A

Quaternary structure - 2a and 2B subunits folded similarly to myoglobin (141aa in a-chain and 146 aa in B)

25
Q

Arrangement of haem groups in haemoglobin

A

One haem group per subunit. Lie on the surface of the molecule far apart in individual pockets

26
Q

Arrangement of the subunits in Hb

A

Hb can be split into 2 halves - a1B1 and a2B2 which are irregular in shape and leave an open central channel when fitted together. Each a subunit is in contact with both B chains. there are few interactions between the 2 a chains or 2 B chains.

27
Q

Difference between peripheral and integral membrane proteins

A

Peripheral proteins lie on the membrane surface while integral proteins lie within the lipid bilayer.

28
Q

What are the two forms of integral membrane proteins that facilitate transport across the membrane?

A

Channel and carrier proteins

29
Q

Describe the 2 mechanisms in which carrier proteins transport molecules

A
  1. Involves one protein which binds, rotates and releases the molecule
  2. Shuttle mechanism involving the molecule being transferred along the chain of proteins
30
Q

Function of messenger proteins

A

allow cells to communicate with each other e.g. hormones

31
Q

In what ways can messenger proteins alter cell activity?

A
  1. influence rate of synthesis of enzymes and other proteins
  2. affect rate of enzymatic catalysis
  3. alter cell membrane permeability
32
Q

Examples of messenger proteins

A

insulin, glucagon, human growth hormone

33
Q

What molecules can hormones be made of?

A

Proteins, amino acid derivatives or steroid

34
Q

How much can enzymes increase the rate of reaction?

A

by up to 10^20

35
Q

What are the monomers of polysaccharides?

A

Monosaccharides / sugars

36
Q

Function of polysaccharides?

A

Storage e.g. glycogen, starch. Structure e.g. cellulose, chondroitin sulphates, peptidoglycan

37
Q

What are the two types of monosaccharides?

A

Aldoses (contain aldehyde -CHO group) and Ketoses (contain ketone -CO group)

38
Q

How are disaccharides formed?

A

Condensation reaction of monosaccharides to produce a glycosidic bond

39
Q

Which monosaccharides make up sucrose?

A

Glucose and fructose

40
Q

Which monosaccharides make up lactose?

A

Glucose and galactose

41
Q

Why are there a huge variety of polysaccharides?

A

Monosaccharides have isomers - e.g. starch is made of a-glucose while cellulose is made of B-glucose

42
Q

Structure of starch

A

Amylose - unbranched, helical chain of a-glucose joined by a 1,4-glycosidic bonds.
Amylopectin - a-glucose molecules joined by a 1,4-glycosidic bonds and a 1,6-glycosidic bonds every 30 molecules to produce a branched structure

43
Q

Structure of glycogen

A

more highly branched than starch - more a 1,6-glycosidic bonds

44
Q

Structure of cellulose

A

Made of parallel polymers of unbranched B 1,4 linked glucose molecules which are held together by H bonds between the OH groups in C3 and C6. About 80 cellulose molecules form a microfibril.

45
Q

Alternative name for fatty acids

A

acyl lipids

46
Q

What molecule are glycerides based on?

A

Glycerol

47
Q

Which diacylglyceride (2 FA) is a major membrane phospholipid?

A

Phosphatidylcholine - made up of 2 fatty acids (hydrophobic tails) and a glycerol, phosphate and choline group (hydrophilic head)

48
Q

Which glycerides are storage molecules?

A

Triacylglycerides (3 FA)

49
Q

What are the 3 main types of lipid?

A

Triacylglycerides (storage), Diacylglycerides (membrane), Sterols (membrane)

50
Q

What feature affects the physical properties of lipids?

A

Degree of saturation (affects London forces)

51
Q

What is the state of saturated fatty acids at room temperature?

A

Solid - lack of kinks in the FA tails allows molecules to pack closely together

52
Q

What is the state of unsaturated fatty acids at room temperature?

A

Liquid - cis C=C cause kinks in the FA tails which prevents the close packing of lipid molecules

53
Q

Function of sterols

A

Can form hormones e.g. oestrogen, cortisol, testosterone. Important in membranes e.g. cholesterol

BDS1 (26 decks)

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