5.2.1

Structure & Functions of Proteins

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Polypeptides

Amino acids are the monomers that join together to form polymers called polypeptides (proteins).

Structure of proteins

Structure of proteins

  • Proteins are made up of amino acids.
  • Dipeptides are formed from the condensation of two amino acids.
  • Polypeptides are formed by the condensation of many amino acids.
Structure of amino acids

Structure of amino acids

  • Each amino acid has a central carbon atom (alpha carbon).
  • There are four atoms or groups of atoms bonded to the central carbon atom:
    • NH2 (an amine group).
    • COOH (a carboxyl group).
    • H (a hydrogen atom).
    • R (a side group).
R groups

R groups

  • The R group is different in each amino acid.
  • The R group determines how the amino acid interacts and bonds with other amino acids in the polypeptide.
Essential amino acids

Essential amino acids

  • There are 20 different types of amino acids that are common in all organisms.
    • 10 of these are essential amino acids in humans because the human body cannot produce them and they are obtained from the diet.
Glycine

Glycine

  • Glycine is an example of an amino acid.
  • Glycine has a hydrogen atom in its R group.
  • Glycine is the only amino acid that does NOT have a carbon atom in its R group.

Peptide Bond

Each amino acid is attached to another amino acid as a result of a condensation reaction. These reactions cause peptide bonds to form.

Polypeptides

Polypeptides

  • Polypeptides are made from chains of amino acids.
  • There are amino acids at each end of the polypeptide chain.
  • These amino acids form the two end terminals:
    • The N-terminal (amine terminal).
    • The C-terminal (carboxyl terminal).
The peptide bond

The peptide bond

  • When two amino acids react together, a bond forms between the carboxyl group of one amino acid and the amine group of a second amino acid.
  • One water molecule is released as a by-product.
  • The bond formed between two amino acids is a covalent bond called a peptide bond.

Function of Proteins

Proteins have a diverse range of functions. Each cell in a living system may contain thousands of proteins, each with a unique structure and function. Functions of proteins include:

Enzymes

Enzymes

  • Enzymes are biological catalysts.
  • Enzymes increase the rate of a reaction without being used up in the reaction.
  • The enzymes are usually tightly folded, complex proteins that are soluble.
Antibodies

Antibodies

  • Antibodies are made up of polypeptide chains.
  • Antibodies are used in the immune response.
  • Antibodies are diverse proteins.
    • Each antibody has a different sequence of amino acids.
Transport proteins

Transport proteins

  • Transport proteins include channel proteins.
  • Channel proteins transport molecules across the cell membrane.
  • Channel proteins transport molecules that are too large to diffuse freely or molecules that carry a charge.
Structural proteins

Structural proteins

  • Structural proteins are long, strong polypeptide chains.
  • Structural proteins are connected by cross-links that hold the chains parallel to each other.
    • E.g. Collagen and keratin.
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1

Unity & Diversity - Molecules

1.1

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Unity & Diversity - Cells

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2.2

Introduction to Cells

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2.5

Structure of DNA & RNA

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2.6

DNA Replication, Transcription & Translation

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Cell Respiration

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Viruses

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3

Unity & Diversity - Organisms

3.1

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3.2

Evidence for Evolution

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3.3

Natural Selection

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Unity & Diversity - Ecosystems

4.1

Classification

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4.2

Cladistics

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4.3

Evolution & Speciation

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4.4

Conservation of Biodiversity

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Form & Function - Molecules

5.1

Carbohydrates & Lipids

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5.2

Proteins

5.2.1Structure & Functions of Proteins
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Form & Function - Cells

6.1

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Form & Function - Organisms

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Gas Exchange

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Transport

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8

Form & Function - Ecosystems

8.1

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8.2

Energy Flow

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Carbon Cycle

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9

Interaction & Interdependence - Molecules

9.1

Enzymes

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9.2

Metabolism

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9.3

Cell Respiration

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9.4

Photosynthesis

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10

Interaction & Interdependence - Cells

10.1

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Adaptation to Environment

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Ecological Niches

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11

Interaction & Interdependence - Organisms

11.1

Integration of Body Systems

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12

Interaction & Interdependence - Ecosystems

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Transfers of Energy & Matter

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13

Continuity & Change - Molecules

13.1

DNA Replication

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13.2

Protein Synthesis

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Continuity & Change - Cells

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Water Potential

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15

Continuity & Change - Organisms

15.1

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15.2

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16

Continuity & Change - Ecosystems

16.1

Natural Selection

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16.2

Stability & Change

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Practice questions on Structure & Functions of Proteins

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What monomers are bonded together to form polypeptides?Multiple choice
  2. 2
    What are the four groups surrounding the central carbon atom in an amino acid?Fill in the list
  3. 3
    How many different amino acids are there? Multiple choice
  4. 4
    Dipeptides are formed by what reaction?Multiple choice
  5. 5
    Which statements are true about the polypeptide chain?True / false
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Starch & Glycogen

Passive Movement Across Membranes