BISC 101 Week 4 Reading

Primary structure of a protein

-The sequence of amino acids in a polypeptide

-Stabilized by peptide bonds only

-order of R groups affects molecule’s functions

e.g. Hemoglobin, has a valine instead of glumate at the 6th position, causing sickle cell.

Secondary structure of a protein

-Formation of a helices and B-pleated sheets in a polypeptide

1. a-helix (alpha-helix), coiled polypeptide backbone.

2. b-pleated sheet (beta-pleated sheet), 180° bent peptide chain that folds.

-Stabilized by hydrogen bonds

Tertiary Structure

A protein’s 3D shape

-has five types of interactions that support its structure

1. Hydrogen bonds

2. Hydrophobic interactions

3. Van der Waal interactions: electrical attractions

4. Covalent bonds

5. Ionic bonds

Quarternary Structure

-Combination of subunits

-Individual subunits are held by tertiary level of bonds

1. Dimers: consists of 2 identical subunits

2. Tetramers: consists of 4 subunits: 2 identical a units and 2 identical b units.

Macromolecular machines

groups of proteins that assemble to carry out a function

Table of protein structures at different levels

Protein fucntions

Catalysis

Defence

Movement

Signalling

Structure

Transport

Substrates

Catalysis

-speeds up reactions

-enzymes: proteins that functions as catalyst

-effective at catalysis due to variety of functional groups present in amino acids

Defence

antibodies

Movement

-moving the cell or large molecules and other types of cargo inside the cell.

e.g: actin and myosin

Signalling

carrying and receiving signals from cell to cell

Structure

Make up body components and form internal skeleton of individual cells

Transport

Allow molecules to enter ot exit cells

carries molecules throughout body

Substrates

-reactants in catalyzed reaction

-binds and reacts at an active site

How enzymes work

-Substrates fit into an enzyme and react (like a key and a lock)

-substrates undergo conformational change so reactants can bind to an active site

-substrates are held in place until transition state is reached

-Lowers activation energy

Transition state

high-energy, unstable state that molecules must reach for a chemical reaction to occur

Activation energy

Minimum energy required to proceed a reaction.

Present in all reactions even if its spontaneous

Free energy

-amt of energy in a system that is usable

-highest during transition state (old bonds broken, new bonds formed)