Proteins

Big Idea 4: Biological Systems Interact

Essential Knowledge• Essential knowledge 4.B.1: Interactions

between molecules affect their structure and function.

• a. Change in the structure of a molecular system may result in a change of the function of the system.

• b. The shape of enzymes, active sites, and interaction with specific molecules are essential for basic functioning of the enzyme.

• Structural support, storage, transport, cellular communications, movement, and defense

against foreigners• Make up more than 50% of dry mass of cells

Protein Functions!

Example: Hemoglobin

• Iron-containing protein found in red blood cells.

• Transports oxygen to body

Antibodies

• Defensive protein fights bacteria and viruses

Example: Antibodies

Example: Lactase, an Enzyme

• Enzyme that helps break down sugar lactose into galactose and glucose. Speeds up reactions rates:

• Lactose intolerant: Mutation of Chrom. 2.• Cramps, bloating, flatulence

• Hormonal protein: regulates sugar in blood (tells cells to take it in), pancreas

Example: Insulin

Polypeptides• Polymers built

from same set of 20 amino acids

• A protein consists of one or more polypeptides

Amino Acid Monomers

Amino Acid Polymers• Amino acids are linked by peptide bonds

Protein Structure and Function

• Consists of 1/more polypeptides twisted, folded, and coiled into a unique shape (determined by amino acid sequence)

Four Levels of Protein Structure

• Primary, Secondary,

Tertiary, Quartenary!

• Watch Videos!

Hollowcylinder

Cap

Chaperonin(fully assembled)

Polypeptide

Steps of ChaperoninAction:

An unfolded poly-peptide enters thecylinder from one end.

1

2 3The cap attaches, causing thecylinder to change shape insuch a way that it creates ahydrophilic environment forthe folding of the polypeptide.

The cap comesoff, and the properlyfolded protein isreleased.

Correctlyfoldedprotein

• Chaperonins are protein molecules that assist the proper folding of other proteins

Sickle-Cell Disease: A Change in

Primary Structure

• A change in primary structure can affect a protein’s structure and ability to function

• Ex: Sickle-cell disease: results from a single amino acid substitution in protein

hemoglobin

Fig. 5-22a

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules donot associatewith oneanother; eachcarries oxygen.

Normalhemoglobin(top view)

subunit

Normal hemoglobin

7654321

GluVal His Leu Thr Pro Glu

Fig. 5-22b

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules interact with one another andcrystallize into a fiber; capacity to carry oxygenis greatly reduced.

Sickle-cellhemoglobin

subunit

Sickle-cell hemoglobin

7654321

ValVal His Leu Thr Pro Glu

Exposedhydrophobicregion

Fig. 5-22c

Normal red bloodcells are full ofindividualhemoglobinmolecules, each carrying oxygen.

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm 10 µm

Messing Up Proteins?• Alterations in pH, salt concentration, temp., or

other environmental factors can cause a protein to unravel denaturation inactive

protein

• Acts as a catalyst to speed up chemical reactions

• Can perform functions repeatedly workhorses!

Enzyme Proteins!

Cofactors

• A non-protein chemical compound required for enzyme activity Ex: Fe

• “Helper Molecules" that assist in biochemical transformations.

Coenzymes

• A protein chemical compound required for enzyme activity

• “Helper Molecules" that assist in biochemical transformations.

Cofactors and Coenzymes

• Work together to regulate enzyme function.• Usually the interaction relates to a structural

change that alters the activity rate of the enzyme

Competitive Inhibitors

• Binding of inhibitor molecule to active site of enzyme prevents binding of the

substrate and vice versa.

Allosteric Competition

• Binding of inhibitor to another (allosteric) site of enzyme (rather than active site) prevents binding of substrate

Model Interpretations

• The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/ or presence of a competitive inhibitor.