Download DNA and the Genetic Code

Proteins, DNA & the
Genetic
Code
By the end of this lesson you should be able to
demonstrate an appreciation of:
• The huge variety of proteins & their diverse properties
• How these depend upon their amino acid sequences
• The “one-gene-one- polypeptide” hypothesis
• What a code does
• The structure of DNA
• How the base sequence of our DNA encodes the
structure of the proteins – which make possible life.
Previous Knowledge:
• Structure of proteins (yr 12)
• Schematic structure of DNA (yr11)
• Cell microstructure (as seen with T.E.M.) (yr 12)
Diverse and Shapely Molecules
Each of the experiments A - E involves one from:
• haemoglobin
• keratin
They are all proteins
• collagen
• gelatine
• catalase
• casein
1. Match one of these chemicals to each experiment
2. What do all these chemicals have in common?
“activ
e site”
Enzymes: e.g. catalase
binds
around . ..
substrate . .
molecule
There are 10 000 different types
of enzyme in your liver cells!
Each one acts as a catalyst to a different chemical
reaction
Casein in Milk
Collagen
Keratin
Haemoglobin
Antibodies
Virus
Antigen binding sites
Antigen
What ever life throws at you –
there’s a protein for it!
Proteins make possible life.
Snakes!
You have beads of four colours, how many
different types of snake, five beads long, can
you make in two minutes?
If you had time and enough beads, how many
different types of five bead snake would it be
possible to make?
1024
45
= 4x4x4x4x4 = 1024
Protein molecules are built from
amino acids – there are 20 types
• There are 20 types of amino acids
• A typical protein is a chain of around 200 amino . ..
. acids.
• How many different proteins are possible?
20200
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20x20
=1607 x 10257
160700000000000000000000000000000000000
0000000000000000000000000000000000000000
0000000000000000000000000000000000000000
0000000000000000000000000000000000000000
0000000000000000000000000000000000000000
0000000000000000000000000000000000000000
000000000000
“One-Gene-One-Polypeptide-Theory”
1024
Archibald Garrod 1909
45
(England)
= 4x4x4x4x4 = 1024
Beadle and Tatum 1941 (USA)
Keratin
How do your hair cells
know how to make your
sort of keratin?
DNA
Cracking the
Code!
Cracking the Genetic Code
• A code stores information in a different form
• A gene is a length of DNA
• Each gene stores the sequence of amino acids
for a particular protein.
• You are about to crack the genetic code!
• You will be able to read a piece of DNA (a gene)
to find the sequence of amino acids it encodes
The name of a famous scientist is
written in Morse code, below.
..-./.-./.-/-./-.-./../…//-.-./.-./../-.-./-.-
Francis Crick
Key:
Part of a DNA
Molecule
Coding
strand
Its sequence
of bases
encodes the
sequence of
amino acids
in a protein
Template
strand
It is used to
make copies of
the coding
strand
Part of a
DNA
Molecule
Coding
strand
Sequence of
bases:
Template
strand
A
G
C
G
T
G
C
T
G
A
C
A
C
G
The Genetic Code:
A triplet of bases on your DNA codes for each type of amino
acid
The 20 Types of Amino Acid
The Genetic Code
(Start)
sequence sequence
of bases of amino
in DNA:
acids in
protein:
DNA Code Key:
(Start)
Triplet of bases
Amino acid
A
G
C
G
T
G
C
T
G
A
C
A
C
G
Ser
Val
Leu
Thr
Insulin
A woman with diabetes
Human
Insulin
Molecule:
Sequence of amino acids
A chain
B chain
1. Choose two contrasting proteins and relate their roles and
properties.
2. Explain what determines their different properties.
3. What is meant by the “one-gene-one polypeptide” theory
4.
Describe how a length of DNA encodes the primary
structure of a protein.
5. The genetic code is “degenerate” and “non-overlapping” what do these terms mean. Explain why each of these is
significant.