BIOCHEM - proteins

protein

naturally occurring unbranched polymer in which the monomer units are amino acids

proteios

a greek word meaning “of first importance”

protein

account for 15% of a cell’s overall mass

protein

are not stored, so they must be consumed daily.

0.8g per kg of body weight

recommended daily intake of protein for adults

Catalytic proteins

classification of enzymes

Defense proteins

classification of immunoglobins or antibodies

transport proteins

classification of hemoglobin, lipoproteins

messenger proteins

classification of insulin, glucagon

contractile proteins

classification of actin, myosin

structural proteins

classification of collagen, α-keratin

transmembrane proteins

classification of protein channels

storage proteins

classification of myoglobin

regulatory proteins

classification of proteolytic enzymes, zymogens

nutrient proteins

classification of casein, ovalbumin

buffer proteins

classification of hemoglobin

fluid balance proteins

classification of albumin, globulin

hemoglobin

transport protein that carries oxygen in the blood

collagen

fibrous protein in connective tissues and it is found in tendons, bone, cartilage, and blood vessels

ferritin

protein that stores iron in the liver

actin and myosin

proteins that control muscle contractions

keratin

fibrous protein in hair, skin, and nails

myoglobin

protein that stores oxygen in tissues

insulin

protein hormone synthesized in the pancreas; controls blood glucose levels

100,000

how many protein classification by shape are there in a human body?

fibrous proteins

Insoluble in water – used for structural purposes (Keratin & Collagen)

globular proteins

More or less soluble in water – used for nonstructural purposes

amino acids

building blocks of proteins

amino acids

contain carboxylic acid and amino groups

amino acids

ionized in solution; soluble in water

amino acids

amino acids

contain a diff side group (R) for each

Nonpolar (neutral), Polar (neutral), Polar Acidic, Polar Basic

classification of amino acids

Nonpolar (Neutral) amino acids

hydrophobic) with hydrocarbon (alkyl or aromatic) sides chains.

Polar (Neutral) amino acids

(hydrophilic) with polar or ionic side chains.

Polar Acidic amino acids

(hydrophilic) with acidic side chains (-COOH).

Polar Basic amino acids

(hydrophilic) with –NH2 side chains.

20 different amino acids

how many amino acids are there?

α amino acids.

the term for the 20 different amino acids

10

how many amino acids are not synthesized by humans?

essential amino acids

amino acids that can’t be synthesized by the human body, thus, must be obtained from diet

glycine

All of the α-amino acids are chiral except …

L isomers

found in the body proteins and in nature.

pH: 6 to 7

isoelectric point (pI)

zwitterion

no net charge (neutral)

pH: 3 or less

-COO- acts as a base and accepts an H+

pH: 10 or higher

-NH3+ acts as an acid and loses an H+

pH of the solution in which it is dissolved

the net charge on an amino acid depends on the…

fixed and constant pI

each amino acid has fixed and constant pI or not

peptide

when an amide links two amino acids it forms…

peptide bond

bond between the COO− of one amino acid and the NH3 + of the next amino acid.

dipeptide

A molecule containing two amino acids joined by a peptide bond.

tripeptide

A molecule containing three amino acids joined by peptide bonds.

polypeptide

A macromolecule containing many amino acids joined by peptide bonds.

protein

A biological macromolecule containing at least 40 amino acids joined by peptide bonds.

c-terminal amino acid

the amino acid at the end of the chain having the free -COO- group (always written at the right).

n-terminal amino acid

the amino acid at the end of the chain having the free -NH3+ group (always written at the left).

enkephalins

pentapeptides made in the brain

enkephalins

act as pain killers and sedatives by binding to pain receptors.

morphine and heroin

addictive drugs that bind to pain receptors, thus producing a similar physiological response, though longer lasting.

endorphins

family of polypeptides of enkephalins

endorphins

are known for their pain reducing and mood enhancing effects.

met-enkephalin

contains a C-terminal methionine

leu-enkephalin

contains a c-terminal leucine

oxytocin and vasopressin

cyclic nonapeptide hormones, which have identical sequences except for two amino acids.

oxytocin

stimulates the contraction of uterine muscles, and signals for milk production; it is often used to induce labor.

vasopressin

antidiuretic hormone (ADH) targets the kidneys and helps to limit urine production to keep body fluids up during dehydration.

conantokins

a small family of helical peptides that are derived from the venom of predatory marine snails of the genus Conus.

conantokins

linear conopeptides 17–27 residues in length that contain multiple γ-carboxyglutamate residues in their sequence.

contulakin-G

a 16 amino acid peptide; discovered over 15 years ago as a member of the neurotensin (NT) family from the venom of predatory marine snail

conus geographus

marine snail

Dr. Lourdes J. Cruz

National Scientist whose research has contributed to the discovery of these peptides

primary, secondary, tertiary, quaternary

structure of proteins

primary structure

The order of amino acids held together by peptide bonds.

primary structure

The backbone of a protein

primary structure

All bond angles are 120o, giving the protein a zigzag arrangement

sulfhydryl

-SH

primary structure of insulin

a hormone that regulates the glucose level in the blood.

primary structure of insulin

Was the first amino acid order determined

primary structure of insulin

Contains two polypeptide chains linked by disulfide bonds (formed by side chains (R).

primary structure of insulin

Chain A has 21 amino acids and chain B has 30 amino acids.

primary structure of insulin

Genetic engineers can produce it for treatment of diabetes.

secondary structure a-helix

A section of polypeptide chain coils into a rigid spiral.

secondary structure a-helix

Held by H bonds between the H of N-H group and the O of C=O of the fourth amino acid down the chain (next turn).

secondary structure a-helix

looks like a coiled “telephone cord.”

secondary structure a-helix

All R- groups point outward from the helix.

secondary structure a-helix

Myosin in muscle and α-Keratin in hair have this arrangement.

secondary structure b-pleated sheet

Consists of polypeptide chains (strands) arranged side by side.

secondary structure b-pleated sheet

Has hydrogen bonds between the peptide chains.

secondary structure b-pleated sheet

Has R groups above and below the sheet (vertical).

secondary structure b-pleated sheet

a typical fibrous proteins such as silk

secondary structure triple helix (superhelix)

3 polypeptide chains (3 a-helix) woven together

secondary structure triple helix (superhelix)

It is found in connective tissues: bone, teeth, blood vessels, tendons, and cartilage; collagen is the most abundant protein

secondary structure triple helix (superhelix)

Consists of glycine (33%), proline (22%), alanine (12%), and smaller amount of hydroxyproline and hydroxylysine; High % of glycine allows the chains to lie close to each other.

secondary structure triple helix (superhelix)

We need vitamin C to form H-bonding (a special enzyme)

tertiary structure

determined by attractions and repulsions between the side chains (R) of the amino acids in a polypeptide chain

hydrophobic interactions

attractions between nonpolar groups

hydrophilic interactions

attractions between polar groups and water

salt bridges

ionic interactions between acidic and basic amino acids

hydrogen bonds

occur between H and O or N