The replication of DNA must be accurate because two identical copies of (replicated) DNA will be used (after the cell division) to encode (→transcription) mRNA. Then, mRNA → translation → proteins. Any errors in DNA replication → changes in sequence of nucleotides of mRNA → changes in sequence of amino-acids → changes in the functional properties of synthesised proteins (→carrier molecules/ enzymes).

P170/Q7

Mucus very thick → difficult to be removed by cilia. Mucus = a perfect growing medium for microorganisms
→ microorganisms multiply → infection.

P171/Q8

A phenylketonuric (PKU) sufferer does not produce phenylalanine hydroxylase (PhAH).

Phenylalanine ~~~~~> Tyrosine by PhAH

Absence of PhAH = no phenylalanine converted to tyrosine. Phenylalanine accumulates in the body
(→ mental retardation in children).

Assignment

P174/Q1		Polynucleotide chain (a polymer) is made of monomers (nucleotides) joint together through a "phosphodiester bridge" (C3 of one sugar and C5 of the next one via the P - group).
P174/Q2	a)	4� = 16
	b)	Number of amino-acids found in living organisms Number of different nucleotides in DNA How is one amino-acid coded for by nucleotides of DNA Number of possible combinations
P175/Q3	a)	AT CG
	b)	parallel - alpha helix
P175/Q4		H- bonds possible between C & G/A & T, but not between A & G (purines)/C & T (pyrimidines)
P175/Q5		Alpha helix folded over and over again

Examinations

P175/Q1

(i) Held together by phosphodiester bridge.

(ii) Hydrogen bond.

DNA → TCGACATGA

(i)

450 / 3 = 150
-1 start codon
-1 stop codon
= 148 codons for amino-acids

P176/Q2

(i)	Nucleic Acid	A	C	G	T	U	Total
	DNA	31	18	22	29	0	100%
	RNA	29	22	18	0	31	100%

(ii)	DNA		RNA
	A (31%)	→	U (31%)
	C (18%)	→	G (18%)
	G (22%)	→	C (22%)
	Th(29%)	→	A (29%)

(i) Thymine absent in mRNA/replaced by Uracil.

(ii) Adenine in mRNA is a transcription of Thymine in DNA.

P176/Q3

Parts to draw: phosphate group - ribose - organic base (Fig 9.2, p.162)

Sequence of nucleotides (A, V, C, G) in RNA
Codons (3 nucleotides of 4) code for one amino-acid
Number of possible codons 4 cube = 64