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polypeptides Flashcards

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1
Q

Define polypeptide

A

a linear organic polymer consisting of a large chain of amino acids, forming part of / all of a protein molecule.

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2
Q

How many proteins to DNA code for in the human body?

A

25000 - 50000

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3
Q

What are the functions of proteins?

A
  • transport
  • regulation
  • growth
  • repair
  • enzyme reactions
  • cell + tissue culture
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4
Q

What are the levels of structure pf a polypeptide ?

A
  • Primary
  • Secondary
  • Tertiary
  • Quarternary
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5
Q

Explain what primary structure is

A
  • sequence of single chain of amino acids = linear

- single change in 1° = profound biological change in overall structure + function

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6
Q

Explain secondary structure

A
  • polypeptide chains dont lie straight

- can for either an alpha helix / beta fold

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7
Q

Describe an alpha helix (secondary)

A
  • spring-like

- H-bonds between C=O and -NH groups to stablise the structure

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8
Q

Describe beta fold (secondary)

A
  • pleated sheets

- H bonds in parallel chains

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9
Q

Explain tertiary structure

A
  • chains to produce 3D shapes
  • chemical + hydrophobic reactions between R-groups keeps structure
  • either forms fibrous proteins or globular proteins
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10
Q

Explain what a fibrous protein is, give examples

A
  • long, coiled chains
  • keratin = hair skin and nails (disulfide bonds due to cysteine - strong inflexible + insoluble)
  • collagen = high quantities in connective tissues for tensile strength (tendons) also resilient sheets support skin + internal organs
  • elastin = resilience + elasticity to tissues and organs (alveoli + blood vessels)
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11
Q

Explain what a globular protein is

A
  • spherical shape
  • water soluble (hydrophobic R groups on inside and hydrophilic on the outside)
  • functions where solubility helps: immunity, muscle contraction and chemical reactions.
  • e.g. enzymes, haemoglobin
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12
Q

What is an example of a globular protein and what is its function?

A

INSULIN

  • hormone = blood glucose regulation
  • soluble; transported in the bloodstream
  • precise shape; fits into specific receptors on membranes
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13
Q

Explain what a conjugated protein is

A
  • a globular protein containing non-protein compound = prosthetic group, attached by covalent bonding and weak interactions
  • lipids combine with proteins = lipoproteins + glycoproteins
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14
Q

What is an example of a conjugated protein and what is its function?

A

HAEMOGLOBIN

  • red oxygen-carrying pigment found in RBC
  • Quaternary
  • 2 alpha + 2 beta subunits - each containing haem group (non-polypeptide)
  • Iron II in haem group - reversibly combining with O molecule
  • main function - transport O2 around body - from lungs to cells where they release it for respiration
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15
Q

What types of bonding are there between R groups of the protein to hold the tertiary structure?

A
  • ionic bonding (between oppositely charged R groups - stronger than h bonds)
  • disulfide bonds / bridges (strongest bond out of all of them - between R groups containing sulfur atoms)
  • hydrophobic + hydrophilic interactions (between polar and non polar r groups)
  • hydrogen bonding (weakest bonds)
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16
Q

Explain quaternary structure

A
  • made up of several polypeptide chains held together by ionic bonds, hydrophobic and hydrophilic interactions, hydrogen bonds and disulfide bonds
  • forms biologically active molecule e.g. haemoglobin = 4 chains together
17
Q

Describe the structure of an amino acid

A
  • carbon atom (C) surrounded by:
  • one amine group (H2N)
  • one carboxylic group (COOH)
  • one hydrogen (H)
  • one R-group (determines type of amino acid)
18
Q

Describe the process of synthesis of a dipeptide

A

CONDENSATION REACTION
- two amino acids joined together by a peptide bond

  • C from carboxylic group forms a peptide bond with N from amine group (C=O + N-H is an amide group)
  • OH from carboxylic group and H from amide group produces water molecule
  • amino acid + amino acid –> dipeptide + water
19
Q

Describe the process of synthesis of a polypeptide

A
  • repeated condensation reactions forming peptide bonds between amino acids
  • R-group interactions between the different r-groups of different amino acids
20
Q

Describe the process of breaking down a dipeptide

A

HYDROLYSIS

  • the addition of water results in a break of the peptide bond
  • OH joins to form a carboxylic group while the H joins to form the amine group
  • dipeptide + water –> 2 amino acids
21
Q

Describe the process of breaking down a polypeptide

A
  • repeated hydrolysis to break peptide bonds and form many individual amino acids
22
Q

What elements make up proteins?

A

C H O N S

23
Q

What is the test for proteins?

A

BIURET TEST
- protein solution with equal volume of biuret reagent

  • positive result = blue to lilac
  • N atoms in peptide bond form purple complex with copper (II) ions in biuret reagent
24
Q

What is an example of an enzyme that is a conjugated protein?

A

CATALASE

  • 4 haem groups each containing iron II which bonds with hydrogen peroxide and speeds up its breakdown.
  • hydrogen peroxide = byproduct of metabolism but is damaging to cells

Biology (11 decks)

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