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Human Biology > Proteins > Flashcards

Proteins Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What percentage of cell dry mass is proteins?

A

Around 50%

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2
Q

What is the size of proteins?

A

Macromolecular
10^3 - 10^6 atoms

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3
Q

How many different types of proteins can the body generate?

A

2 million from 20,000 genes

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4
Q

How many amino acids form a polypeptide that can fold?

A

> 40

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5
Q

All amino acids except which have a chiral centre?

A

Glycine

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6
Q

What 2 forms can amino acids exist in?

A

L and D enantomers

(L dominates D as D are rare in nature)

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7
Q

From where was tyrosine first isolated?

A

Cheese

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8
Q

Non polar R groups of amino acid result in?

A

Hydrophobic properties - 6 of these

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9
Q

What R groups of amino acids make it hydrophilic?

A

Polar (6)
Acidic (2)
Basic (3)

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10
Q

Learn the amino acids

A

Non polar - slide 13
Acidic - slide 15
Basic - slide 16
Polar - slide 17 and 18

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11
Q

Where do disulfide bridges form?

A

Between cysteine –SH groups (Cys-S—S-Cys)

covelant crosslinks

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12
Q

What reaction forma disulfide bridges?

A

Oxidation

(Reduction breaks them)

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13
Q

Learn abbreviations for amino acids

A

Slide 20

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14
Q

What is the name of bond between 2 amino acids?

A

Peptide

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15
Q

Peptides with more than how many amino acids are regarded polypeptides?

A

10 (decapeptides)

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16
Q

What are 2 properties of peptide bonds?

A

Rigid and planar

Caused by bond resonance

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17
Q

The action of virtually all proteins involves what?

A

Binding of a ligand

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18
Q

What is a ligand?

A

The substance that is bound by the protein.
Eg. Ion, small molecule or macromolecule

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19
Q

What is the order of sequence of amino acids?

A

N-terminus to C-terminus

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20
Q

What is sickle cell disease an example of?

A

Mutation in primary structure - single mutation in Hba haemoglobin gene

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21
Q

How many amino acids per turn of an alpha helix?

A

3.6

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22
Q

What are alpha helixis abundant in and absent in?

A

Abundant - haemoglobin
Absent - chymotrypsin (digestive enzyme)

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23
Q

How many runs does beta pleated sheet have?

A

5 -10

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24
Q

What are multiple B pleated sheets connected by?

A

Short runs or “hairpin loops”

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25
Q

Which one of B sheets or a helices are more flexible?

A

B sheets

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26
Q

What are characteristics of loops / random coils?

A
  • Usually located on surface
  • Rich in polar and charged residues
  • Length = 2-20 residues
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27
Q

What typically causes differences between structurally similar proteins?

A

Loops /random coils

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28
Q

What is the name given to the groupings of structural elements?

A

Super secondary structures /motifs

(Occur in many globular proteins)

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29
Q

What is the beta-hairpin motif?

A
  • Two antiparalell B strands joined by hairpin loop
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30
Q

What are the characteristics of beta-hairpin loop motif?

A
  • Simplest supersecondary structure
  • Common in globular proteins
  • No specific function associated with this motif
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31
Q

What is the helix-loop-helix motif and its 2 functions?

A

Two α-helices connected by a loop

Functions as either DNA-binding (e.g. c-Myc) or Ca2+-binding motif (e.g. calmodulin)

32
Q

Where is the helix-loop-helix motif commonly found?

A
  • Transcription factors (helix-basic loop-helix)
  • Cell signalling proteins that bind Ca2+ (EF-hand)
33
Q

What is the greek key motif?

A

Particular arrangement of 4 beta-strands into an antiparallel beta-
sheet

Common in range of proteins (e.g. proteases [trypsin], cytokines [TNFalpha])

No specific function associated with this motif

34
Q

What is the coiled coil motif?

A

2–7 alpha-helices are coiled together like the strands of a rope.

Usually contain repeats of a 7 residue pattern; heptad repeat (hxxhcxc)
h=hydrophobic, c=charged, x=any

35
Q

Give examples of coiledcoil motif

A
  • Leu zippers in transcription factors [e.g. c-Fos and jun]
  • Structural proteins [Myosins]
36
Q

What is the zinc finger motif?

A

Two anti-parallel beta-sheets followed by 1 alpha-helix, stabilised by a zinc ion

  • May bind Fe, Zn or no metal at all
  • Metal binding mediated by Cys (in beta-sheets) and His (in alpha-helix)
37
Q

What are the fuctions of Zinc finger motifs?

A

Functions: Binding of DNA, RNA, lipid and protein substrates

38
Q

What is the B barrel motif?

A

Multiple anti-parallel beta-sheets that twist to form a closed structure

First strand is hydrogen bonded to the last

39
Q

What are the 4 types of beta barrel motifs?

A

– Greek key barrel
– Up-and-down barrel
– Jelly roll barrel (complex)
– Beta-helix barrel

40
Q

What are the water channels in the pores of beta barrel motif called?

A

aquaporins

(learn 2 structures on slides 43 and 44)

41
Q

What is a domain?

A

A polypeptide chain (or part of chain) that folds independently into a stable
structure with its own hydrophobic core

42
Q

What is a doimain formed from?

A

Several simple motifs and secondary structure elements

43
Q

How many domains can a protein have?

A

1-7 domains

each is associated with a distinct biological function

44
Q

Give an exaple of a domain

A

Src homology 2 (SH2) domain – binds phospho-Tyr residues

Important in insulin signalling

45
Q

What do Ionic bonds in the tertiary structure form?

A

Between CO2- and NH3 of R Groups

electrostatic attraction

46
Q

How do hydrophobic interactions occur?

A

Hydrophobic R Groups cluster inside proteins to shield themselves from water

Van der Waals interactions

47
Q

Which structure is a fibrous protein?

A

Secondary. Forms long parallel fibres and sheets. These are usually insoluble in water

48
Q

What is the important role of fibrous proteins? 2 examples?

A

Provides support and strength

  • Collagen
  • Keratins
49
Q

What are the 2 types of keratin?

A

Alpha keratin - in mammals hair and nails

Beta keratin:
- invertebrate silks, reptile scales, and claws
- Avian feathers, beaks and claws

50
Q

What is the structure of collagen?

A

Super-helices of Gly-rich triple alpha-helices (tropocollagen)

Assembles into fibrils

51
Q

What is collagen for?

A

Main protein in connective tissue

Supports, connects or separates tissues and organs

52
Q

What are the properties of collagen?

A
  • Strong and elastic
  • very abundant (25% of total protein)
53
Q

What is collagen found in?

A

Bone
Cartilage
Ligaments
Tendons

Teeth
Blood vessels
Skin
Eyes (cornea and lens)

54
Q

What is the name of the syndrome associated with collagen?

A

Ehlers Danos Syndrome (EDS)

55
Q

What can EDS affect?

A
  1. Skin
  2. Musculoskeletal
  3. Cardiovascular
56
Q

What is the structure of alpha keratin?

A

Coiled coils of two alpha-helices that assemble together to form large fibres

57
Q

What are the properties of alpha keratin?

A

(Found in hair and nails)

  • Strong and inextendable
  • insoluble and chemically inert
  • disulphide bridges cross link coiled-rings
58
Q

What is beta keratin aka? Where is it found?

A

Fibroin

Found in silk and spider webs

59
Q

What is the structure of Fibroin?

A

Layers of antiparalell beta sheets rich in Ala and Gly residues

Small side chains interlock allowing close packaging of B sheets

Sheets joined by amorphous streches - This gives elasticity and stregnth

60
Q

What is a globular protein?

A

A mixture of irregularly folded secondary elements that form a 3D shape.

These are usaully soluble in water -Inner hydrophobic cor and transported easily in body fluids

61
Q

Give 3 examples of globular proteins

A

– Myoglobin
– Haemoglobin
– Immunoglobulins

62
Q

What is haemoglobin made of and what is its function?

A

4 haem molecules (polypeptide chains) - porphyrin ring +Fe2+ (binds to O2)

Transports oxygen from lungs to rest of body for aerobic respiration

63
Q

What ere 2 mutations in Hb DNA that cause disease?

A
  • Sickle cell disease
  • Thalassaemias
64
Q

What is sickle cell disease?

A

– Single mutation in DNA coding within beta-globin gene
– Non-sense mutation = changes primary sequence

65
Q

What are the effects/symptoms of Sickle cell disease?

A
  • Changed RBC shape (sickle shaped)
  • RBCs rigid, become bloced by capillaries
  • Increased haemolysis (RBC destruction) - Anaemia/spleen damage
66
Q

What is the mutation in Sickle cell disease?

A

Single mutation in beta-globin gene

(T to A) changes 10 sequence (Glu to Val)

67
Q

What is an Immunoglobin?

A

Y-shaped proteins of the immune system which
identify and combat invading foreign organisms

68
Q

How are the 4 chains in immunoglobins linked?

A

By disulfide bridges
– 2 large H (heavy) chains
– 2 short L (light) chains

69
Q

What gives each immunoglobin a speciic binding site shape (antigens)?

A

VAriable structures in heavy and light chains

70
Q

What engages an immunoglobin for attack?

A

Constant portions of the heavy chains

71
Q

What happens to Ionic bonds in altered pH?

A

– Break ionic bonds
– Disrupts tertiary structure
– Can render proteins insoluble in water and precipitate out of solution

72
Q

What does low pH do to an Ionic bond?

A

– Low pH = high H+ concentration (acidic)
– Adding H+ neutralises the COO- part of the ionic bond removing its charge

73
Q

What does a high pH do to Ionic bonds?

A

– High pH = low H+ concentration (alkaline)
– Removes H+ - neutralises the NH3+ part of the ionic bond removing its
charge making it NH2

74
Q

What is pyrexia?

A

increased body temperature, fever
(used as ancient anti-viral defence mechanism)

75
Q

Which organic solvents can denature a protein?

A

Ethanol, acetone, phenol

Human Biology (7 decks)

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