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BIOLOGY PRESENTATIONS
FOR A-LEVEL, IN MULTIMEDIA
JAMES BOWLES, 2001
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‘A’ Level Biology
Nucleic Acids
Nucleotides
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A nucleotide contains:
Phosphate Group
Pentose Sugar
Base
O
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Nucleotides
The phosphate group gives
the nucleotide an acidic
nature
O
O P OO
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Nucleotides
The pentose sugar may be
either Ribose (RNA) or
Deoxyribose (DNA)
O
H
OH
Ribose
O
H
H
Deoxyribose
Nucleotides
There are five bases
Adenine
Purines
Guanine
Cytosine
Thymine
Pyramidines
Uracil
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Polynucleotides
O
O
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Bonds can form
between carbon 3
of the pentose
sugar and the
phosphate group
on carbon 5 of an
adjacent
nucleotide
Polynucleotides
O
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O
O
O
O
O
O
Long chains
can be built up
in this way Polynucleotides
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5’ OPolynucleotides
The
ends
of
O
these
chains
are
O
named on the
O
basis of which
O
carbon is not
O
involved in
bonding
O
3’
DNA
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Deoxyribonucleic Acid
Sugar is
Deoxyribose
Bases are:
O
H
H
Cytosine Thymine Adenine Guanine
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O
O
DNA
O
O
O
O
O
O
O
O
O
O
O
O
Two chains of
polynucleotide
run anti-parallel
to one another
DNA
The chains are
arranged as a
DOUBLE
HELIX with 10
bases to each
complete turn
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DNA
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Base pairing is complimentary
Adenine
Thymine
Guanine
Cytosine
The bonds are hydrogen bonds
RNA
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Ribonucleic Acid
Sugar is
Ribose
Bases are:
Cytosine Uracil
O
H
OH
Adenine Guanine
Messenger RNA
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Messenger RNA
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mRNA
U A AGC G UA U UGGC A UG
Single-stranded, uncoiled
polynucleotide
Messenger RNA
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mRNA
U A AGC G UA U UGGC A UG
mRNA is a copy of the
DNA code which is
exported from the nucleus
Transfer RNA
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tRNA
Single-stranded RNA
arranged in a ‘clover leaf’
shape
Transfer RNA
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tRNA
Amino Acid
binding site
tRNA attaches to amino
acids in the cytoplasm
Transfer RNA
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tRNA
Anticodon
The anticodon lines up alongside
the appropriate codon on mRNA
during protein synthesis
Ribosomal RNA 21
rRNA
This is a long length of RNA
produced in the nucleolus
Ribosomal RNA 22
rRNA
It has areas of single and double
helices
Ribosomal RNA 23
rRNA
In the cytoplasm it combines
with proteins to form ribosomes
DNA vs. RNA
DNA
RNA
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DNA vs. RNA
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DNA
RNA
Always a double helix
May have single or
double helix
DNA vs. RNA
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DNA
RNA
Always a double helix
May have single or
double helix
Sugar is deoxyribose
Sugar is ribose
DNA vs. RNA
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DNA
RNA
Always a double helix
May have single or
double helix
Sugar is deoxyribose
Sugar is ribose
Bases are A, T, G & C Bases are A, U, G & C
DNA vs. RNA
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DNA
RNA
Always a double helix
May have single or
double helix
Sugar is deoxyribose
Sugar is ribose
Bases are A, T, G & C Bases are A, U, G & C
Permanent
May be temporary
DNA vs. RNA
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DNA
RNA
Always a double helix
May have single or
double helix
Sugar is deoxyribose
Sugar is ribose
Bases are A, T, G & C Bases are A, U, G & C
Permanent
May be temporary
Chemically very
stable
Chemically less stable
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