Proteins

What proteins are made up of

Have an amino group, an acid, a hydrogen, carbon molecule, and a carbon side chain

Can also contain sulfur, phosphorus, or iron

How proteins are connected

Peptide bonds connect the acid end of one amino acid with the amino end of another

They are links that form a protein chain, which can be simple or very complex

Essential vs non-essential amino acids

Nonessential → can be made within the body

Essential → cannot be made in the body (must be obtained from foods)

How amino acids are held together

Held together by peptide bonds:

• water cna hydrolyze a bond and break the amino acids apart (e.g. digestion)

• Dehydration can make a bond (protein synthesis)

Organization of Proteins

Properties of amino acids (e.g. polar vs non-polar) create attractions between AA

• causes folding, bending

• Secondary and tertiary structure

Four Levels of Protein Structure: Primary Structure

Unique sequence of amino acids in a polypeptide

Linear organization

Four Levels of Protein Structure: Secondary Structure

Folding or coiling of the polypeptide

Includes the a helix and the B pleated sheet

Four Levels of Protein Structure: Tertiary Structure

3-D shape of a polypeptide

Results from interactions between amino acids and R groups

Four Levels of Protein Structure: Quaternary Structure

Overall protein structure

Made of two or more polypeptides

Proteins as a building material

• a matrix of protein underlies almost all body structures → e.g. bones, muscles, ligaments, hair, nails, etc

• New proteins are requires for growth and tissue maintenance → GI tract cells are replaced every 3 days, the whole body has its cells renewed every 7 years

Proteins as enzymes

Enzymes are usually composed of a protein, a vitamin, and a trace material

• they act as catalysts, allowing reactions to occur more quickly and efficiently

An enzyme is not affected by the chemical reactions it allows the take place

Proteins as peptide hormones

Growth hormone

Insulin and glucagon

Thyroxin (amine hormone)

Calcitonin and PTH

ADH

(Fast-acting, short half-life)

Roles of Protein: regulation of fluid balance

Plasma proteins exert a colloid osmotic effect

• pulling fluid from the tissue back into the blood

Roles of Proteins: acid-base regulation

Proteins act as buffers accepting and releasing hydrogen ions thus preventing acidosis or alkalosis

Transport proteins

Channels → e.g. Na+ and K+ channels

Carriers → e.g. glucose carrier

Active transporters → e.g. Na/K ATPase pump

Proteins in immunity

Antibodies are proteins that bind up specific invaders like viruses or antigens

• antigens are substances that antibodies bind to. They may include bacteria, allergens, toxins, or anything that causes an inflammatory response

Roles of Proteins: source of energy

• proteins can be broken down into amino acids and converted to other proteins

• Some amino acids can be used within metabolism for energy

• They can be also converted to sugars or stored as fats

Protein metabolism

Deamination is the removal of the nitrogen containing amino group, converting it to ammonia, which is sent to the liver and converted into urea. The remaining carbon fragment may be used for energy or stored as fat

• amino acids can be used to make fat by removing the amino group and converting the remaining carbon fragments to fat

Other roles of protein

Can be converted to other proteins or make:

• neurotransmitters norepinephrine and epinephrine

• Melanin

• Fibrin

• Precursor to the vitamin niacin

Collagen (what it is and where’s its found)

Most abundant protein in vertebrates

Found in:

• cartilage

• Tendons

• Bones

• Teeth

• Skin

• Blood vessels

At least 18 different types of collagen

Collagen molecular structure

Molecules arranged in staggered pattern

Also relatively resistant to enzymatic breakdown

Types of Collagen (I, II, III, IV, V)

Type I → arteries, tendons, ligaments, skin, organs, bone

Type II → cartilage

Type III → alongside type I

Type IV → cell basement membranes

Type V → cell surfaces, hair, placenta

Vitamin C characteristics

Water-soluble:

• cannot be stored for long (~ a month)

• Symptoms can be seen 4-6 weeks after a deficiency begins (recovery is also relatively quick)

Most animals have the ability to make their own (not humans)

Elastin

Fibrous protein

Found in soft tissues → skin, blood vessels, and lungs

Elastin structure

Tropoelastin fibres → cross-linked

Random coil structure → little secondary structure

Very extensible

Elastic recovers

Proteoglycans

Hydrophilic molecules

Bonds with water

Allowing tissues to hold on to water → might otherwise be squeezed out by compression

Keratin

Hard, strong, but extensible

Made up of protein molecules → can align themselves into fibrous crystals

High stiffness (around 10GPa)

E.g. hair

Silk Protein - Fibroin

Form spider webs, cocoon, and nests

B-sheet structures

• glycine on one hand

• Alanine/serine on the other

• Sheets stack on top of each other

• Bulky regions interrupt sheets and allow for stretchiness

Hemoglobin characteristics

4 subunits containing Heme groups

• contains iron for O2 binding

• Each hemoglobin can bind 4 O2 molecules

Each RBC contains about 200 million molecules of hemoglobin

How hemoglobin is affected by pH

PH changes will affect affinity of Hb

High H+ (low pH) shifts curve to the right → decreases affinity for O2

• allows for more unloading of O2 in the tissues

• Bohr’s law

How hemoglobin is affects by CO2 and temp

High altitudes causes release of DPG (right shift)

Exercise:

• higher temp, higher CO2, and higher H+ (lower pH)

  • These will shift curve to the right and decrease affinity of O2 for Hb

  • More unloading and O2 delivery to tissues

Fetal hemoglobin

Has a higher affinity for O2 than adult Hb

Can pull O2 from maternal RBC’s and move it to fetal RBC’s

Protein Energy

Daily normal requirement → 50g protein (10% of 2000kcal diet)

Proteins are needed for growth and maintenance and for fighting infections

• acute protein energy malnutrition → children are thin for their height

• Chronic protein energy malnutrition → children are short for their age