Part 4: Ch 5STRUCTURE & FUNCTION OF PROTEINS

9/06/2016

AP Bio Vocabulary of the Day

(Stems, Prefixes, and Suffixes…Oh my!)

bath- depth

Example: bathysphere (a deep-sea

submersible lowered on a cable)

Fabulous Fact

The African Elephant gestates for 22

months. The short-nosed Bandicoot has

a gestation period of only 12 days.

You Must Know…

To understand the structure and function of

proteins.

AP Biology Standards addressed: Big Idea 2

People to Ponder

Frederick Sanger

Sanger was born in 1918 in Rendcombe, England.

Sanger’s father was a doctor and wanted his son to follow in his footsteps.

Sanger enrolled at Cambridge and became interested in nature and science. He decided to

study this because a career in science gave him a better chance of being a problem solver.

His decision was probably made harder and easier when both of his parents dies of cancer his

first two years at Cambridge.

When WWII broke out in Europe Sanger registered as a conscientious objector due to his

Quaker upbringing.

Sanger joined the Cambridge Scientists Anti-War Group and there met his future wife Joan

Howe who was also studying at Cambridge.

Sanger and Joan married after he graduated in 1940. They went on to have three children:

Robin (1943), Peter (1946), and Sally Joan (1960).

Frederick Sanger

Sanger went on to get his Ph.D. at Cambridge studying amino acid metabolism. He continued

his studies afterwards and worked on identifying free amino groups in insulin.

Through his research Sanger figured out how to order amino acids and became the first person

to sequence a protein.

Sanger’s work proved that proteins were ordered molecules and therefore genes and DNA also

had to have an order and sequence.

Sanger was awarded the Nobel Prize for Chemistry in 1958 for determining the structure of a

protein.

In 1951 he began working for the Medical Research Council at Cambridge. In 1962 they

moved to join the Lab for Molecular Biology where Francis Crick and others worked on DNA-

related problems.

Sanger started to work with RNA because it was smaller and developed the dideoxy method

that was transferable to DNA and is the most common method for sequencing reactions today.

Sanger won a second Nobel Prize for Chemistry (shared with Walter Gilbert and Paul Berg) in

1980 for contributions to determining the base sequence of nucleic acids.

Frederick Sanger

Sanger is the 4th person to win two Nobel Prizes and one of only two people to win twice in the

same category (the other is John Barden in Physics).

He retired in 1985 and spent most of his time working in the garden.

Sanger credited his wife for being the supportive presence that made his work and life possible.

He turned down knighthood because he didn’t want to be addressed as “Sir” and be seen as

different and set apart.

In 1992 the Welcome Trust and Medical Research Council established the Sanger Centre. It’s

focused on furthering knowledge of genomes and was key in the Human Genome Sequencing

Project.

Sanger died in his sleep in November 2013.

He described himself as “just a chap who messed about in the lab…academically not brilliant.”

Sanger is remembered as “a true ‘gentle’ man, extremely courteous and charming.”

(www.dnaftb.org)

I. Proteins

• “Proteios” = first or primary

• 50% dry weight of cells

• Contains: C, H, O, N, S

Myoglobin protein

Protein Functions (+ examples)

• Enzymes (lactase)

• Defense (antibodies)

• Storage (milk protein = casein)

• Transport (hemoglobin)

• Hormones (insulin)

• Receptors

• Movement (motor proteins)

• Structure (keratin)

Overview of protein functions

Overview of protein functions

Protein Structure and Folding

Proteins are constructed of amino acids bonded together.

Anatomy of an amino acid:

Amino group (NH2)

Carboxyl group (COOH)

R group (side group- unique to each type of amino

acid)

Carbon in the center bonded to all groups and one H

Structure has been studied in depth using X-ray

crystallography

Phenylalanine

Primary Structure- a chain of amino acids bonded together via dehydration synthesis

(polypeptide chain)

The bonds between amino acids are called peptide

bonds

The sequence of the amino acids determines the

shape and type of protein.

Secondary Structure- coiling and folding of the chain of amino acids – gains 3-D shape. The

result of H-bonds.

Alpha (α) helix: coiled chain

Beta (β) pleated sheet: folded sheets

Basic Principles of Protein Folding

A. Hydrophobic AA buried in interior of protein

(hydrophobic interactions)

B. Hydrophilic AA exposed on surface of protein

(hydrogen bonds)

C.Acidic + Basic AA form salt bridges (ionic bonds).

D. Cysteines can form disulfide bonds. This creates

more stability in the protein shape.

Tertiary Structure- folded chain with the overall shape of the protein.

Involves the interaction of the R groups

Often reinforced with disulfide bridges

Can also involve H-bonds, ionic bonds, and

hydrophobic interactions

Quaternary Structure- 2 or more polypeptide chains and possibly nonpolypeptides collected

into one macromolecule.

example: hemoglobin

example: collagen fibers

amino acids polypeptides protein

Bonding (ionic & H) can create

asymmetrical attractions

The shape of a protein determines the function of a

protein and is INCREDIBLY important.

There is folding assistance to ensure correct shape.

Chaperonins- protein molecules that assist in the

folding of other proteins.

Proteins can lose their shape (denature) when

conditions change- change in pH, temperature, etc.

• Protein structure and function are sensitive to chemical and

physical conditions

• Unfolds or denatures if pH and temperature are not optimal

change in structure = change in

function

Modified from Anna VanDordrecht (SCOE)

& Mrs. Chou (Longmont High School)