Topic 2.4: Protein

Polypeptides

  • chains of amino acids
  • main component of proteins

Amio acids 1200px-AminoAcidball.svg
Linked together by ribosomes during translation

Condensation
reaction involves amino group and carboxyl group, in which water is eliminated and peptide bond between 2 amino acids is formed


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Dipeptide - 2 a.a
Polypeptide - many

There are 20 amino acids in polypeptides synthesized on ribosomes
R-group makes each amino acids chemically different
==> determine the characteristics of polypeptides

Why do most organisms make proteins using the same 20 amino acids?
1) The 20 a.a were produced by chemical properties before the origin of life --> all organisms used them
2) The 20 a.a is ideal --> natural selection will always favor organisms that use them
3) Life evolved from a single ancestral species that used the 20 a.a


Genes
A cell produces polypeptides w/ thousands of different sequences which are coded in the base sequence of gene
--> 3 bases of the gee are needed to code for each amino acid in polypeptide #

Base sequence

  • located at both ends and middle of gene sequences
  • this is the only sequence that actually codes for polypeptide

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Proteome

  • all of the proteins produced by a cell, a tissue or an organism
  • variable
  • none of us have identical proteomes

Conformations

  • 3D structure which is determined by a.a sequence
  • Shape and chemical properties are depended on R-groups

Functions

Denaturation

  • a structural change in a protein that results in a permanent loss of biological properties.

Structure

Collagen: A component of the connective tissue of animals (most abundant protein in mammals)

Spider silk: A fiber spun by spiders and used to make webs (by weight, is stronger than kevlar and steel)

Hormones

Insulin: Protein produced by the pancreas and triggers a reduction in blood glucose levels

Glucagon: Protein produced by the pancreas that triggers an increase in blood glucose levels

Immunity

Immunoglobulins: Antibodies produced by plasma cells that are capable of targeting specific antigens

Transport

Haemoglobin: A protein found in red blood cells that is responsible for the transport of oxygen

Cytochrome: A group of proteins located in the mitochondria and involved in the electron transport chain

Sensation

Rhodopsin: A pigment in the photoreceptor cells of the retina that is responsible for the detection of light

Movement

Actin: Thin filaments involved in the contraction of muscle fibres

Myosin: Thick filaments involved in the contraction of muscle fibres

Enzymes

Rubisco: An enzyme involved in the light independent stage of photosynthesis