PBO W9 PROTEINS pt 2

SECONDARY STRUCTURE OF PROTEINS

arrangement in space adopted by the backbone portion of a protein

SECONDARY STRUCTURE OF PROTEINS

The two most common types : alpha-helix (a-helix) and the beta-pleated sheet (b-pleated sheet).

alpha-helix (a-helix) and the beta-pleated sheet (b-pleated sheet)

SECONDARY STRUCTURE OF PROTEINS types

SECONDARY STRUCTURE OF PROTEINS

hydrogen bonding between a carbonyl oxygen atom of a peptide linkage and the hydrogen atom of an amino group of another peptide linkage farther along the protein backbone

Alpha-helix (a-helix)

A single protein chain adopts a shape that resembles a coiled spring (helix)

Alpha-helix (a-helix)

– H-bonding between same amino acid chains

–intra molecular – Coiled helical spring

– R-group outside of the helix -- not enough room for them to stay inside

Beta-Pleated Sheets

which two fully extended protein chain segments in the same or different molecules are held together by hydrogen bonds

Beta-Pleated Sheets

H-bonding between two different chains – inter and/or intramolecular

Beta-Pleated Sheets

Side chains below or above the axis

Unstructured protein segment

is a protein secondary structure that is neither an a helix nor a b pleated sheet

TERTIARY STRUCTURE OF PROTEINS

the overall three-dimensional shape of a protein that results from the interactions between amino acid side chains (R groups) that are widely separated from each other within a peptide chain.

TERTIARY STRUCTURE OF PROTEINS

Results from the interactions between amino acid side chains (R groups) that are widely separated from each other.

Disulfide bond

covalent, strongest, between two cysteine groups

Electrostatic interactions: AKA: Salt Bridge

between charged side chains of acidic (R)and basic (R)amino acids

H-Bonding

weak bond, between polar, acidic and/or basic R groups

-OH, -NH2, -COOH, -CONH2

H-Bonding examples

O, N or F

r H-bonding to occur, the H must be attached on

Hydrophobic interactions

Between non-polar side chains

1. Disulfide bond

2. Electrostatic interactions

3. H-Bonding

4. Hydrophobic interactions

Four Types of Interactions

Electrostatic interactions

Salt Bridge between charged side chains of acidic and basic amino acids

multimeric protein

Quaternary structure of protein refers to the organization among the various peptide chains in a

QUATERNARY STRUCTURE OF PROTEINS

Highest level of protein organization

QUATERNARY STRUCTURE OF PROTEINS

Present only in proteins that have 2 or more polypeptide chains (subunits)

QUATERNARY STRUCTURE OF PROTEINS

Subunits are generally independent of each other - not covalently bonded

QUATERNARY STRUCTURE OF PROTEINS

Proteins with quartenary structure are often referred to as oligomeric proteins

QUATERNARY STRUCTURE OF PROTEINS

Contain even number of subunits

Elongated shape simple, regular linear structures single type of secondary structure

Fibrous Protein SHAPE/ STRUCTURE

Generally insoluble

Fibrous Protein SOLUBILITY WITH WATER

Fibrous Protein

Tend to aggregate together to form macromolecular structures, e.g., hair, nails

structural (provide support and external protection)

Keratin Collagen Elastin Myosin Fibrin

Fibrous Protein examples

keratins

found in wool, feathers, hooves, silk, and fingernails

collagens

found in tendons, bone, and other connective tissues

elastins

found in blood vessels and ligaments

myosins

found in muscle tissue

fibrin

found in blood clots

Collagen

Most abundant proteins in humans (30% of total body)

Collagen

Major structural material in tendons, ligaments, blood vessels, and skin

30%

Collagen percentage in body

triple helix

Collagen Predominant structure

Glycine (1/3) and proline (1/3)

These are important in Collagen to maintain structure

spherical or globular shapes

several types of secondary structure

Globular Protein SHAPE/STRUCTURE

SOLUBILITY WITH WATER

Globular Protein

Globular Protein

hydrophobic amino acid residues in the protein core

Globular Protein

enzymes and intracellular signaling molecules

Globular Protein

metabolic chemistry, performing functions such as catalysis, transport, and regulation

insulin

regulatory hormone for controlling glucose metabolism

myoglobin

involved in oxygen storage in muscles

hemoglobin

involved in oxygen transport in blood

transferrin

involved in iron transport in blood

immunoglobulins

involved in immune system responses

Myoglobin

An oxygen storage molecule in muscles.

Myoglobin

Monomer - single peptide chain with one heme unit

Myoglobin

Binds one O2 molecule

Myoglobin

Has a higher affinity for oxygen than hemoglobin

Myoglobin

Oxygen stored in myoglobin molecules serves as a reserve oxygen source for working muscles

Hemoglobin

An oxygen carrier molecule in blood

Hemoglobin

Transports oxygen from lungs to tissues

Hemoglobin

Tetramer (four peptide chains) - each subunit has a heme group

Hemoglobin

Can transport up to 4 oxygen molecules at time

Hemoglobin

Iron atom in heme interacts with oxygen

associated with cell membranes

Membrane Protein SHAPE/STRUCTURE

Insoluble in water

Membrane Protein SOLUBILITY WITH WATER

Membrane Protein

hydrophobic amino acid residues on the surface

Membrane Protein

Help in transport of molecules across the membrane

Proteins

play crucial roles in most biochemical processes.

proteins

The diversity of functions exhibited by ____ far exceeds the role of other biochemical molecules

• Ability to bind small molecules specifically and strongly

• Ability to bind other proteins and form fiber-like structures, and

• Ability integrated into cell membranes

The functional versatility of proteins stems from:

Catalytic proteins

nzymes are best known for their catalytic role

Defense proteins AKA Immunoglobulins or antibodies

are central to functioning of the body’s immune system.

Transport proteins

Bind small biomolecules, e.g., oxygen and other ligands, and transport them to other locations in the body and release them on demand (eg. Hgb, transferrin, HDL and LDL)

Messenger proteins

transmit signals to coordinate biochemical processes between different cells, tissues, and organs.

Insulin and glucagon

regulate carbohydrate metabolism

Human growth hormone

regulate body growth

Contractile proteins

Necessary for all forms of movement.

actin and myosin

Muscles contain filament-like contractile proteins such as

contractile proteins

Human reproduction depends on the movement of sperm – long flagella made up of

Structural proteins

Confer stiffness and rigidity

Collagen

is a component of cartilage

a-Keratin

gives mechanical strength as well as protective covering to hair, fingernails, feathers, hooves, etc.

Transmembrane proteins

pan a cell membrane and help control the movement of small molecules and ions

Storage proteins

Bind (and store) small molecules

Ferritin

an iron-storage protein - saves iron for use in the biosynthesis of new hemoglobin molecules.

Myoglobin

an oxygen-storage protein present in muscle

Regulatory proteins

Often found ―embedded in the exterior surface of cell membranes - act as sites for messenger molecules (eg insulin) can bind and initiate the effect it carries

Regulatory proteins

Often the molecules that bind to enzymes (catalytic proteins), thereby turning them ―on and ―off and thus controlling enzymatic action.

Nutrient proteins

Particularly important in the early stages of life - from embryo to infant

Casein (milk) and ovalalbumin (egg white)

Examples of nutrient proteins

Milk

also provide immunological protection for mammalian

Buffer proteins

part of the system by which the acid–base balance within body fluids is maintained

Hemoglobin

Buffer proteins example

Fluid-balance protein

help maintain fluid balance between blood and surrounding tissue

albumin and globulin

Fluid-balance protein example

Hydrolysis of proteins

reverse of peptide bond formation

Hydrolysis of proteins

Results in the generation of an amine and a carboxylic acid functional groups.

enzyme-catalyzed hydrolysis

Digestion of ingested protein is

Free amino acids

produced are absorbed into the bloodstream and transported to the liver for the synthesis of new proteins.

continuous process

Hydrolysis of cellular proteins and their resynthesis is a

Complete protein hydrolysis

all peptide bonds are broken

Partial protein hydrolysis

some, but not all, of the peptide bonds are broken