Nucleic acids
 DNA
& RNA
 Made up of nucleotides:
phosphate
base
pentose sugar
Nucleotides
2
types of base:
 Pyrimidines
-
 Cytosine
C
T
 Thymine
 Purines
 Adenine
 Guanine
A
G
Complimentary base pairing
 Adenine
will only bind with Thymine
 Cytosine will only bind with Guanine
T
A
C
G
DNA structure
nucleotide
Condensation
polymerisation of the
deoxyribose nucleotides
Replication—worksheet hw
 During
cell division the DNA must
replicate
 The enzyme helicase unwinds the DNA
double helix
 The exposed bases bind to free floating
nucleotides in the nucleoplasm
 DNA polymerase binds the
complimentary nucleotides
 Replication is
semiconservative
The genetic code
 The
sequence of nucleotide bases
forms a code
 Each ‘code word’ has three letters– a
triplet code
 Each codon codes for a specific amino
acid e.g:
 GGG
= proline
 CGG = glycine
 ATG = tyrosine
 ACT = stop (no amino acid)
Protein synthesis
 The
DNA codes for
proteins
 A copy of DNA
(mRNA) is made in
the nucleus
(transcription)
 The mRNA is used
to make a protein
(translation) in the
cytoplasm
Transcription
 Helicase
unwinds the
DNA
 Free nucleotides join
onto complimentary
bases
 RNA polymerase links
adjacent nucleotides
 The completed mRNA
moves out of the
nucleus
Transcription
Three types of RNA
 Messenger
RNA- made in the nucleus
but sent to the ribosome mRNA
 Ribosomal
RNA- makes up the
ribosome (site of protein synthesis) with
protein rRNA
 Transfer
RNA-brings the appropriate
amino acid to the ribosome for protein
synthesis tRNA
Translation
 mRNA
binds to a ribosome
 tRNA carries an amino acid to the
ribosome
Amino acid
activation
 transferRNA:
 tRNA
binds onto a
specific amino acid
Translation
A
second tRNA brings another aa
 The two amino acids bind
 The process repeats
Translation
A
polypeptide chain forms
 Eventually a stop codon is reached
Acknowledgements

.
Animated cell models used by kind
permission of The Virtual Cell website:
Quiz

a)
b)
c)
d)
1. Which process involves tRNA:
transciption
translation
DNA replication
gene mutation
Quiz

a)
b)
c)
d)
2. The formation of RNA does not
involve:
ribose sugar
thymine
removal of water
phosphate