Lecture 3

Question 1

What are the four main biological compounds in a cell?

Answer 1

• Lipids (fatty acids, fat and phospholipids)
• Carbohydrates (sugars and polysaccharides)
• Nucleic acid and nucleotides
• Proteins, peptides and amino acids

Question 2

Define lipids

Answer 2

Soluble in non-polar solvents e.g. benzene - practically insoluble in water

Question 3

LIPIDS: Define fatty acids

Answer 3

• Fatty Acids - carboxylic acids (COOH group)
  => saturated fatty acid- C-C single bonds e.g. stearic acid
  => unsaturated fatty acid - saturated(single C bond) replaced by double C bond e.g. oleic acid
  => hydrophobic - hydrocarbon chain, hydrophilic - carboxyl group
  => when placed at air-water interface, monolayer formed =polar carboxyl in contact with water, nonpolar hydrocarbon tail faces away from water

Question 4

LIPIDS: Define micelles

Answer 4

• lipid low water solubility
• Conc > solubility limit = micelles spontaneously formed (spherical)
• Micelle structure - hydrophilic end contacts water, hydrophobic ends close together to minimise water contact

Question 5

LIPIDS: Define fats

Answer 5

Esters formed by condensation of fatty acids with glycerol

=> broken down by fat-splitting enzymes in digestive system

Question 6

LIPIDS: Define phosphoglycerides and describe their shared properties with a part of the cell.

Answer 6

Similar in structure to fat but different in functions
=> phosphate molecule replacing one of fatty acid branch in fat molecule
=> form lipid bilayers = properties shared with cell membrane - high electrical resistance and capacitance, cell walls of viable organisms become leaky when mild heat/chemicals applied

Question 7

LIPIDS: Define fat-soluble vitamins

Answer 7

Organic substances, necessary for normal cell function
=> fat soluble are lipids = e.g. vitamin A,E etc. - insoluble in water but dissolve inorganic solvents
=> water soluble vitamins not lipids- e.g. vitamin C

Question 8

Define carbohydrates and its functions. What is the general formula?

Answer 8

· Organic compounds found in plant, animal cells
- General formula = (CH_2 O)_n
Functions - energy source(sugars), energy storage and structural purposes (polysaccharides)

Question 9

CARBOHYDRATES: Define monosaccharides

Answer 9

• Smallest carbohydrate (3-9 carbons)
• 2 types - ALDOSES (aldehyde group e.g. glucose), KETOSES (ketone group e.g. fructose)
• D-glucose = most common, ring structure, biologically active

Question 10

CARBOHYDRATES: Define disaccharides

Answer 10

• Disaccharides - formed when aldehyde/ketone group from one monosaccharide reacts with hydroxyl group from another, water molecule removed (condensation reaction)
• Oligosaccharides - short chain of repeating monosaccharides
  Polysaccharides - long chain of repeating monosaccharides or disaccharides

Question 11

CARBOHYDRATES: What is cellulose?

Answer 11

Most abundant organic compound on earth, water insoluble. Crystalline structure from hydrogen bonding

Question 12

Define nucleic acids

Answer 12

· DNA (deoxyribonucleic acid) and RNA(ribonucleic acid)

- Polymers made up of subunits called nucleotides

Question 13

What is the structure of nucleotides?

Answer 13

• Phosphoric acid
• Five carbon sugars
• Nitrogen base

Question 14

What are the nitrogen base pairs in DNA and RNA?

Answer 14

DNA

• Adanine and Thymine (A&T)
• Cytosine & Guaninane (C&G)

RNA

• Adanine and Uracil (A&U)
• Cytosine & Guaninane (C&G)

Question 15

Describe the function of DNA

Answer 15

· DNA function - nucleus contains most DNA carrying hereditary info
=>plasmids manipulated and the recombinant plasmids are introduced into living cells
=> function of DNA - store RNA molecule synthesis instructions with specific length and nucleotide sequences, then involved in variety of protein synthesis , gene - segment of DNA coding for RNA molecule sequence

Question 16

Describe the function of RNA

Answer 16

RNA - reading and implementing genetic instructions of DNA, single stranded
=> messenger RNA(mRNA) - carries info about protein sequence to ribosomes
=> ribosomal RNA (rRNA) - forms up to 65% of ribosomes
=> transfer RNA (tRNA) - smallest (70-95 nucleotides)

Question 17

Define proteins.

Answer 17

· Large biopolymers - roles include: contribute to cell membrane structure, motive functions
· Formed from group of 20 amino acids (long chain)
· Simple proteins formed by condensation of amino acids
Polypeptides - short condensation chains of amino acids

Question 18

What is the structure of a protein?

Answer 18

• Primary - particular sequence of amino acids joined through peptic bonds
• Secondary - structural configuration of amino acid residues are close neighbours
• Tertiary - folding, bending of polymer chains as well as hydrophobic and hydrophilic interactions
• Quaternary - proteins may consist of more than one polypeptide chains

Question 19

Define cell metabolism

Answer 19

All chemical reaction processes that occur in the cell, cell constituents converted to different compounds

Question 20

Define metabolic regulation

Answer 20

The role of enzymes:

• Enzymes are conjugated proteins which are biological catalysts
• Highly specific enzymes

Question 21

Define central dogma and its 3 main processes.

Answer 21

· Central dogma - conversion of genetic code held within cell DNA into protein which controls process within the cell
- 3 main processes
=> replication - info stored in DNA replicated by forming identical molecule
=>transcription - info segments contained in DNA copied onto strands of RNA
=>translation - info used to make polypeptides/proteins with specific sequence by RNA sequence

Question 22

Define anabolism

Answer 22

Anabolism - (or biosynthesis) - production of complex biological polymers and requires energy e.g. photosynthesis

Question 23

Define catabolism

Answer 23

Catabolism - process that occurs within cell whereby larger complex compounds are broken down into smaller simpler products and releases energy for the cell