Chemistry of Proteins

1 Chemistry of Proteins

Outline

Protein Uses

Amino Acids
- Structure, Classification, Properties

Peptides and Proteins
- Structure, Classification, Properties

Metabolism

Diet
- Starvation, Diabetes, and Atkin's Diet
- Vitamins

2 Protein Uses

Structure - Some proteins (collagen, silk, ...) provide protection and support

Catalysis - Enzymes are proteins the direct and accelerate biochemical reactions.

Movement - Proteins are involved in all cell movements

Defense - Blood-clotting, keratin in skin, ...

Regulation - Peptide hormones (such as insulin) regulate key biochemical processes

Transport - Proteins can assist movement of molecules into and out of cells or through body.

3 Amino Acids

Optically active

Mirror image is NOT the same.

In lab, get 50/50 mixture.

In nature, ``all'' amino acids are ``L'' (left-handed)

4 Classification of Amino Acids

Non-polar (10)

Ala, Cys, Gly, Ile, Leu, Met, Phe, Pro, Try, Val

Don't contain any polar groups on side chain

Water insoluble side chains

Polar (10)

Arg, Asn, Asp, Gln, Glu, His, Lys, Ser, Thr, Tyr,

Includes Neutral, Acidic, and Basic side chains

Water soluble side chains

5 Amino Acid Structures

6 Amino Acid Structures (2)

7 Classification

# amino acids	Name	Examples

1	amino acid	-
~ 2-50	peptide	oxytocin, GSH, insulin
~ 50+	protein	hemoglobin, collagen

8 Peptide Bond

Peptides and Proteins are held together by peptide bonds.

The peptide bond is formed by the reaction of the carboxylic acid group of one amino acid with the amine group of the second amino acid.

9 Collagen - Fibrous Protein

Collagen is a primary component of connective tissue

10 Hemoglobin - Globular Protein

Hemoglobin is responsible for the transport of oxygen.

11 Essential Amino Acids

Humans are unable to synthesis nine (9) of the twenty (20) naturally-occurring amino acids in sufficient quantities, so these essential amino acids must be supplied in our diets.

Histidine	(basic)	Phenylalanine	(non-polar)
Isoleucine	(non-polar)	Threonine	(polar)
Leucine	(non-polar)	Tryptophan	(non-polar)
Lysine	(polar)	Valine	(non-polar)
Methionine	(non-polar)

Meat is a good source of protein. Vegetarians need to be sure to consume ``complete proteins'' in order to avoid malnutrition.

12 Metabolism

Both Carbohydrates and Lipids (triglycerides & fatty acids) are converted into acetyl-CoA, which feeds into the Kreb's cycle to produce energy. However, only carbohydrates are able to produce oxaloacetate, which is necessary to keep the Kreb's cycle going. If necessary, proteins can be used to synthesize oxaloacetate, which can be used to either keep the Kreb's cycle going or to synthesize glucose.

13 Starvation

Carbohydrate reserves depleted in about 1 day.

Metabolism of lipids (fat) predominates.

Protein (primarily from muscle) sacrificed to provide glucose for brain.

14 Diabetes

Untreated diabetes similar (from a metabolism perspective) to starvation.

Blood sugar is high (especially after eating) because either insulin is not formed (Type I) or insulin receptors broken (Type II). Insulin is responsible for bringing glucose from bloodstream into cells.

Since cells think glucose concentration is low, hormones released to produce more glucose.

Cell concentration of glucose is low, so metabolism of fats primary fuel source.

High metabolism of fat can lead to ketone bodies (acetone smell on breath).

15 Atkin's Diet

The Atkin's Diet, Protein Power Plan, and other diets require:

Very low carbohydrate intake

High fat intake (for fuel)

High protein (to avoid muscle degradation)

Claim is that we consume too much simple sugar, which gives rise to diabetes.

American Heart Association recently warned that these diets can be dangerous.

16 Energy Expenditures

Activity	Calories/min (180 lb person)

Aerobics (vigorous)	11
Basketball (vigorous)	15
Bicycling (11 mph)	9
Jogging (10 min/mile)	14
Running (7 min/mile)	18
Swimming (fast)	13
Walking (20 min/mile)	5

Taken from ACS Textbook ``Chemistry in Context'', 3rd Edition, Table 11.6 (p. 441)

17 Exercise and Calories

One pound of fat @ 3500 Calories

If 180 pound person runs 3 miles a day, 7 days a week he/she will use:

(7 min/mile) * (21 miles) = 147 minutes

(18 Calories/min) * (147 minutes) = 2646 Calories

But only ~ 1/3 of these are due to fat.

2646 / 3 = 882 Calories of fat per week

To lose 1 pound fat

(3500 Calories) / (882 Calories/week) @ 4 weeks

Exercising this much will allow you to lose 1 pound of fat per month!

18 Metabolism

Basal Metabolism - Energy required to survive (heart, lungs, ...)

For most individuals:

Basal Metabolism = 1 [ Cal/kg hr]

Thus, for our 180 pound individual:

180 lbs @ 80 kg

1 [ Cal/kg hr] x 80 kg x 24 hours = 1920 Calories/day.

A key role of exercise is to increase basal metabolism. Direct calorie burning helps, but alone is not enough.

File translated from T_EX by T_TH, version 3.02.
On 14 Apr 2003, 14:08.