Chapter 6Chapter 6Chapter 6Chapter 6

Proteins and Amino AcidsProteins and Amino Acids

General Amino Acid Structure

HN C C

H O

OH

H

Aminogroup

Acidgroup

Side Group Varies

Examples of amino acids

HN C C

H

O

OH

C

H

O OH

HH

HN C C

H

O

OH

CH3

HHN C C

H

O

OH

H

H

HN C C

H

O

OH

C

H

HH

HN C C

H

O

OH

C

H

HH

SH

HN C C

H

O

OH

C

H

CH3

OHH

Glycine Alanine

AsparticAcid

Phenylalanine Cysteine Threonine

Condensation of two amino acids:

Formation of a dipeptide

HN C C

H

O

OH

CH3

H HN C C

H

O

OH

C

H

HH

HN C C

H

O

CH3

H H

N C C

O

OH

C

H

HH

Alanine Phenylalanine

+

+ H2O

PeptideBond

Formation of a Polypeptide

11 H2O

AA1 AA2 AA4 AA7AA6AA3 AA5 AA8 AA10AA9 AA11 AA12++++++ +++++

AA1---AA2---AA3---AA4---AA5---AA6---AA7---AA8---AA9---AA10---AA11---AA12

Folding andShape of Proteins

Essential versus Non-essential Amino Acid

Humans need ALL 20 amino acids to be able to make proteins.

Glycine Alanine SerineCysteine Proline TyrosineAspartic Acid Asparagine Glutamic AcidGlutamine Arginine

Valine Leucine IsoleucineThreonine Methionine PhenylalanineTryptophan Lysine Histidine

Essential Amino Acids

Conditionally Essential Amino Acids

HN C C

H

O

OH

C

H

HH

HN C C

H

O

OH

C

H

HH

OH

Phenylalanine Tyrosine

Human enzymephenylalanine hydroxylase

Protein digestion in the GI Tract

Mouth - moisten and mechanical crushing

Stomach - HCl denatures proteins - HCl also converts pepsinogen into pepsin - pepsin acts to cleave large polypeptides into smaller polypeptides

Protein digestion in the GI Tract

Small Intestine - Trypsin and chymotrypsin breakdown polypeptides into smaller and smaller peptides. - Carboxypeptidases and aminopeptidases “chew” along from the ends to liberate amino acids. - Di- and tripeptidases break down dipeptides and tripeptides to amino acids. - Free amino acids are absorbed into the blood system.

Protein synthesis: Transcription

Making messenger RNA

CellDNAmRNA

Protein synthesis: Translation

Ribosomes “translate” the CODE of the message utilizing transfer RNAs which

carry individual amino acids

Transfer RNA

Amino Acid

Ribosome

mRNA

Protein synthesis

Growing protein strand

Protein Function Within Our Body

1) Building materials

(e.g. collagen, elastin, keratin, myocin, actin)

2) Enzymes(e.g. lipase, amylase, pepsin)

3) Hormones(e.g. insulin, glucagon, CCK)

4) Regulators Fluid balance

5) Transport: i.e. hemoglobin, ferritin

Iron atom

Heme

Normalversus

Sickle Cells

Normal Hemoglobin Val-His-Leu-Thr-Pro-Glu-Glu-

Sickle Cell Hemoglobin Val-His-Leu-Thr-Pro-Val-Glu-

6th residue

A Membrane-bound transport protein“Sodium - Potassium Pump”

OUTSIDE CELL

INSIDE CELL

6) Acid-Base Regulators

8.0

7.45

7.35

6.8 Death

Death

Acidosis

Alkalosis

Normal

7) Antibodies (Immune system)

8) Energy: - break down protein to use

the energy.

Proteins per ServingIn Food Groups

Gra

ms

Quality of Proteins

• A COMPLETE protein contains essential amino acids is relatively the same amounts as humans need.

(e.g. meat, fish, poultry, eggs, milk)

• However, all proteins do not have the same proportion of each amino acid.

IleIle LysLys MetMet TrpTrp

LegumeLegume YESYES YESYES NONO NONO

GrainsGrains NONO NONO YESYES YESYES

TogetherTogether YESYES YESYES YESYES YESYES

© 2002 Wadsworth Publishing / Thomson Learning™

PEM (Protein-Energy Malnutrition)

• affects 1 out of 4 children in the world.

• accomplice in 50% of the 10.9 million child deaths each year.

• 70% in Asia, 26% in Africa & 4% in Latin America

PEM (Marasmus)

• chronic PEM

•6 - 18 months

• inadequate intake of energy and protein.

PEM (Kwashiorkor)

• acute PEM

• sets in at 18 months - 2 years of age

• inadequate intake of protein due to a change from breast milk to protein poor cereals.

Protein and Amino Acid Supplements

what is the RDA for protein?

what happens when more high protein higher amounts of proteins are consumed?

do athletes need to supplement their diet with higher amounts of protein or amino acid?

Types of Vegetarianism

Omnivores - people that eat ALL foods including meat.

Lactoovovegetarians - exclude meat, poultry, fish, and seafood.

Lactovegetarians - also exclude eggs

Vegan - exclude ALL animal derived foods

Vegetarians obtain their protein from whole grains, legumes, nuts, vegetables, and, in some cases, eggs and milk products

Food Pyramids Compared