Human Biochemistry

Question 1

Product of the condensation reaction of 2-amino acids to form polypeptides

Answer 1

dipeptide

a substituted amide made up of two amino acids joined by a peptide bond or a peptide linkage

Question 2

Explain primary structure of proteins

Answer 2

Simply the sequence of amino acid residues that form the protein

Indicated by using three-letter codes for the amino acids

Question 3

Explain the secondary structure of proteins

Answer 3

manner in which the polypeptide chain folds itself due to intramolecular hydrogen bonding

Affects arrangement in space of the polypeptide chain

alpha helix and beta pleated sheets

Question 4

Explain alpha helix

Answer 4

Resembles a right handed spiral staircase or coiled spring

Can make the protein elastic or sponge-like in fibrous proteins such as hair and wool

Maintains its shape through regular intramolecular hydrogen bonds

hydrogen bond between negative polar side O of the carbonyl group (C=O) and the positive polar side of the -NH2 group of the third peptide bond down the chain

Question 5

Explain beta-pleated sheet

Answer 5

Different polypeptide chains are bound together by hydrogen bonds to create an orderly alignment of protein chains in which the direction of H-bonding is perpendicular to the sheet structure giving rise to a repeating, pleated pattern.

Question 6

Explain tertiary structure of proteins

Answer 6

Folding or curling due to the interaction between the sequence of amino acids that maintains the three dimensional shape of the protein.

Amino acid chains interact in 4 ways to stabilize their shapes

1) covalent bonding (disulfide bridges)
2) H-Bonding between NH2 and COOH
3) salt bridges (electrostatic attraction) between NH3 and COO- groups
4) R group side chain depending on its polarity

Question 7

Explain Quaternary Structure

Answer 7

How the polypeptide subunits are held together in a precise, more complex 3-D structural arrangement

Occurs only in proteins that are composed of more than one polypeptide chain which are held together by non-covalent bonds

Consist of hydrophobic interactions, H-bonding and ionic bonds

Question 8

What is a subunit?

Answer 8

When a protein consists of more than one polypeptide chain, each polypeptide chain is a subunit

Question 9

What is denaturation?

Answer 9

When proteins lose their 3-D structure and hence biological activity

Question 10

Why does denaturing affect the functioning of a protein

Answer 10

The exact shape is the key to the function of each of the numerous proteins in the body.

Most common cause of denaturing is heat, as in the case when an egg is fried or boiled

Question 11

Explain analysis of proteins through chromatography

Answer 11

Used for analyzing separation of mixtures of substances which are otherwise not easily separated

Paper chromatography - relative solubility of different amino acids varies in the stationary phase (water, which is absorbed on the cellulose paper) and in the mobile phase (solvent)

Amino acids with greater solubility in the eluting solvent will travel further in the direction of the solvent flow

Ratio of fronts = distance travelled by compound/distance travelled by solvent

Question 12

Electrophoresis

Answer 12

Method of separating molecules on the basis of their electric charges

In order to analyze a protein using electrophoresis, the peptide bonds in the protein must first by hydrolyzed to release the individual amino acids

Question 13

List the major functions of proteins in the body

Answer 13

Proteins carry out many important functions in the body

Structural - collagen (skin) keratin (hair)

biological catalysts - enzymes

hormones - insulin

antibodies - proteins that are produced as a result of the presence of foreign materials in the body

transport - hemoglobin

energy - proteins in the human body can be used to provide energy

Question 14

carbohydrates

Answer 14

Main energy source for our bodies and are vital to the synthesis of cells.

Serve as food sources for living organisms and provide the structural support for plants.

Most carbohydrates are changed to glucose through digestion

Cellulose is the major component of plant cells that cannot be digested by humans; it does provide fiber

Question 15

Describe the structural features of monosaccharides

Answer 15

Smallest molecular units of carbohydrates with the general formula (CH2O)n where n=3 to 9

Aldehydes or ketones containing a carbonyl group and at least 2 hydroxyl groups

(glucose, galactose)

Question 16

List the major functions of carbohydrates in the human body

Answer 16

energy source - potatoes, bread, corn, rice contain carbohydrates

energy reserve - animals use glycogen stored in the liver as their energy storage polysaccharide; can be broken down by enzymes into glucose

precursor of other biologically important molecules - found as components of nucleic acids

Question 17

Describe the importance of a diet high in fiber

Answer 17

Water insoluble fiber - provide bulk and move food through digestive system

water soluble fiber - includes pectins which undergo fermentation in the large intestine by bacteria to produce short-chain fatty acids (propanoic and butanoic acids) both help stabilize lipid and blood glucose levels

help prevent constipation and diverticulosis

IBS - refers to symptoms arising from the bowel not working as it should

Obesity - excess body mass; high fiber leads to feeling full on a diet with reduced carbohydrates and fats

Crohn’s Disease - inflammatory bowel disease; dietary fiber may help prevent

Haemorrhoids - enlarged blood vessels in and around the rectum that are swollen and can cause bleeding; caused by pressure in the abdomen due to constipation

Question 18

Define lipids

Answer 18

substances found in living organisms that are defined in terms of their solubility: in general these are poorly soluble in water, but soluble in organic solvents which are non-polar or of low polarity

Due to large non-polar hydrophobic hydrocarbon chains

Question 19

What are the groups that lipids are divided into?

Answer 19

triglycerides (fats and oils)
phospholipids (complex lipids containing phosphorus)
steroids (cholesterol)

Question 20

Why are linoleic and linoeic acids vital?

Answer 20

They cannot be synthesized in our bodies, but are necessary for its correct functioning

Question 21

Define the term iodine number

Answer 21

Number of grams of iodine that react with 100g of lipid/fat/oil

Question 22

How to find iodine number of linoleum acid

Answer 22

100 g/ Mr

100/280.4

Question 23

Describe how oral contraceptives function in the female body

Answer 23

Changes release of hormones (FSH and LH) from hypothalamus/ pituitary gland

Prevents ovulation/egg release

Prevents attachment of egg to uterus/ endometrium

Prevents sperm from reaching the egg by thickening the cervical mucus

Question 24

Describe characteristics of an enzyme such as pepsin

Answer 24

Enzymes are proteins

Enzymatic activity depends on tertiary and quaternary structure/the nature of the active site
Lock and key/ induced fit hypothesis

Question 25

Compare a biological enzyme to an inorganic catalyst

Answer 25

Enzymes function within a narrow pH range
Enzymes are denatured by high temperatures above 40C

Inorganic catalysts can be used at high temps because they are less affected by conditions

Enzymes are very specific and inorganic catalysts often catalyze several reactions/non specific

Question 26

Describe the characteristic properties of 2-amino acids

Answer 26

amino acids are colorless, crystalline solids that exist as zwitterions (dipolar ions)
explains their relatively high melting points for organic compounds and why they are generally more soluble in water than in organic solvents

Amphoteric

When R is not H, the 2-Carbon atom is chiral, the molecule is asymmetric and gives rise to two possible stereoisomers (enantiomers)