Lecture 8: Proteins

CGI Proteins

Crash Course Biomolecules

Learning Objectives: Proteins

• Outline the role of condensation and hydrolysis in the relationship between amino acids and polypeptides

• State that there are 20 different amino acids that can be used to make polypeptides synthesized on ribosomes.

• State the amino acid sequence of polypeptides is coded for by genes.• Define proteome• Explain how amino acids can be linked together in any sequence giving a

huge range of possible polypeptides.• Explain the four levels of protein structure, explaining the significance of

each level.• Explain the significance of polar and non-polar amino acids• List the functions of rubisco, insulin, immunoglobulins, rhodopsin, collagen

and spider silk.• Define denature and discuss how temperature or pH affect protein structure

and function.

Proteins are sequences of amino acids that are held together by peptide bonds.

Feathers are a type of protein.

Diverse classes of proteins do diverse jobs.

Hemoglobin is a transport protein and moves O2 around the body.

Horns and skin and eye pigments and eye lashes and hair and scales are types of proteins.

Enzymes are a type of protein that makes or breaks specific covalent bonds.

Covalent bonds require energy to form and release energy when they are broken.

• Enzymes are required to make/break covalent bonds.

Example: sucrase enzyme breaks apart sucrose into glucose and fructose.

Overview of Protein Diversity and Function

Overview of protein diversity and function

Some vegetable proteins are incomplete and a balanced diet requires complementary

proteins for good health.

Amino acid structure

What element is found in proteins that is absent in the CHOs and Lipids?

A: Carbon

B: Hydrogen

C: Oxygen

D: Nitrogen

E: All of the above

20 different amino acids found in

proteins differ in their shape and electrical

charge.

Excellent movie of protein structure here!

Amino acids link by covalent peptide bonds in the C terminus direction.

Primary structure of a protein: unique sequence of amino acids in a polypeptide

Oligopeptide vs. polypeptide

Secondary structure formed by hydrogen bonds between carboxyl and amino groups.

Tertiary structure formed by interactions between side chains of amino acids.

Does cooking change the amount of protein/amino acids in the eggs?

A: Yes, raw eggs have more protein than hard boiled eggs do. When the egg is cooked, the proteins leak out into the boiling water.

B: No, the amount of protein in the eggs is the same. The protein cannot disappear!

C: Not sure.

Protein tertiary structure and function is maintained by weak molecular interactions that can be denatured by

– Temperature– Changes in pH or high

[H+] – High concentrations of

polar or non-polar substances.

Denaturing a protein destroys its ability to function but does not digest the protein!

Quaternary structure: multiple polypeptide chains join together to make a functional

protein.

Ribbon Diagram of sucrase shows overall structure of the protein. Structure of antibody directs its function!

DNA nucleotide sequences

code for the sequences of amino acids

that make up proteins.

ATC: Collagen and Cellulose

Which bonds are created during the formation of the primary structure of a protein?

A) peptide bonds B) hydrogen bonds C) Ionic bonds D) Sulfer bonds E) A, B, and C

What maintains the secondary structure of a protein?

A) peptide bonds B) hydrogen bonds C) disulfide bonds D) ionic bonds E) All the above

At which level of protein structure are interactions between the side chains (R groups) most important?

A) primary B) secondary C) tertiary D) quaternary E) all of the above

The effect of changing one amino acid in a polypeptide consisting of 325 amino acids

A) The primary structure of the protein would be changed.

B) The tertiary structure of the protein might be changed.

C) The biological activity or function of the protein might be altered.

D) Only A and C are correct. E) A, B, and C are correct.