14. Chemical composition of the cell. Basic chemical compounds. Lipids, proteins and nucleic acids

Question 1

What are cells made up of - what four organic biomolecules are made from these elements?

Answer 1

• Hydrogen
• Oxygen
• Nitrogen
• Carbon
• Sulphur
• Phosphorus

99% of the cell = water molecules

Cells usually contain more protein than DNA

Many diseases are due to abnormalities in biomolecules, chemical reactions or biochemical path-ways.

When the elements are combined - organic biomolecules. There are four key areas:

1. Nucleic acids
2. Proteins
3. Lipids
4. Carbohydrates

Question 2

Chemical Comp of NA?

Answer 2

Very large molecules

• A Macromolecule made up of chains of monomeric (single protein) nucleotides
• The most common Nucleic Acids are RNA and DNA.

Nucleotides consist of three components:
•5-C sugar
•1 Phosphate group
•and a Nitrogenous base (A, G, C, T (DNA) or U (replace T) (if RNA). Inosine is a rare NA base in mature transfer RNA

The structure of the carbon sugar determines the type of nucleic acid

• 2-deoxyribose - DNA
• Ribose (without a hydroxyl group) - RNA.

Nucleic acids can be:

• Single or double stranded
• Although 3 or more strands can form
• In double stranded nucleic acid (e.g. DNA) 2 strands are held together by Hydrogen bonds.

The Sugar-phosphate ‘backbone’ is held together by phosphodiester linkages

Question 3

How can a certain folding form tRNA and rRNA?

Answer 3

RNA is usually single stranded but any strand may fold back upon itself = forming a secondary structure –> tRNA and rRNA

Question 4

What RNA is in retroviruses?

Answer 4

RV has single stranded RNA as their genome

Question 5

Points of RNA?

Answer 5

• RNA acts as a messenger b/w DNA and ribosomes
• essential carrier molecules for AA to be used in protein synthesis
• three types of RNA:
• tRNA
• mRNA
• rRNA

Question 6

Points of DNA?

Answer 6

NA containing genetic instructions used in the development/functioning of all organisms.
Role of DNA mole - the long term storage of information - instruction to construct components of the cell (e.g. proteins/ RNA molecules).

DNA segments that carry this genetic information - genes

Othe DNA sequences have structural purposes/ involved in regulating the use of the genetic info

DNA - phosphate back bone x 2 = two chains held together by HB b/w complementary bases - chains coil around eachother = DNA double helix

GC
AT

Question 7

Proteins? 2 categories?

Answer 7

Proteins w/in cells - 2 categories:

• Integral - sit incorporated w/in plb
• Peripheral - show loose association w/ 1 of the 2 membrane surfaces
• Bonded to membrane by hydrophobic reactions b/w lipids and non-polar AA (outer regions of protein)

Question 8

Protein Functions?

Answer 8

Functions:

• Resp for acting as receptors - bind to a sig molecule –> induce biochemical response in cell
• Proteins in cell wall add stiffness/rigidity to cell (e.g. globular proteins)
• Motor proteins - myosin (muscles) generating mechanical forces

Question 9

Chemical composition of Proteins? Types of Proteins?

Answer 9

• NH4 (AMINO)
• COO (CARBOXYL)
• H
• R GROUP (VARIES)

20 Naturally occurring amino acids

Types:

• Skeletal - collagen
• Muscle - myosin
• Blood Plasma - fibrin
• Soluble proteins
• Compound protein

Question 10

Transmembrane proteins?

Answer 10

some integral proteins span the mem 1 or more times - one side to other. Permanently attached. These are one -pass/ multipass transmembrane proteins

• Large enough to extend across 2 lipid layers - can protrude from mem surfaces

Question 11

Movement of proteins in the membrane?

Answer 11

• Some not bound rigidly and can move w/in plane of cell mem

- Most are restricted in lateral diffusion by attachment to cytoskeletal components

Question 12

Chemical comp of Lipids? General points?

Answer 12

• H, O, C
• Form half of the phospholipid bilayer
• Glycolipids: Phospholipid w/ direct carbohydrate attached to it
• Oligosaccharide chains extend outwards from surface = promoting lipid asymmetry

Question 13

Major classes of cellular lipids?

Answer 13

The major classes of cellular lipids are:

-Phospholipids
o Have a phosphate head and a lipid tail, help form the membrane

-Glycolipids
o Have one or several sugar units attached

-Fatty acids
o Contain an even number of carbon atoms attached

• Phosphoglycerides
  o Have carboxylic acids attached, a key part of biosynthesis of other molecules

-Sphingolipids
o An amino acid with an unsaturated hydrocarbon chain

-Sterols
o Includes things such as cholesterol and forms part of the membrane