Download DNA-and-Chromosome

(2) STRUCTURE AND REPLICATION
OF DNA
(A) DNA
Structure
DNA
(B)
Chromosome
Structure
(C) DNA
Replication
STRUCTURE AND REPLICATION OF
DNA (A+B)



Describe the structure of DNA in terms of
nucleotides, backbone and complementary base
pairing
State how 2 DNA strands are held together
Describe the antiparallel structure of the DNA
strands

State where genetic information is stored
Define the term ‘genotype’
State what the genotype is determined by
State what the molecule of inheritance is

Describe the structure of a chromosome



1= Nucleotides 2= DNA double helix 3=Genes 4=Chromosomes
5= Nucleus of cell 6=You!
WHAT IS DNA & WHY IS IT
IMPORTANT?
All cells store their genetic information in the base
sequence of DNA, which is found inside the
nucleus.
 DNA is the molecule of inheritance and within the
structure of DNA, there are many instructions to
make specific proteins.

The sequence of DNA determines the genotype
 The genotype is the term given to the genes
that are present in an organisms.
 The genotype determines the order of amino acids
 The order of the amino acids determines the type
of protein that is to be made.

STRUCTURE OF DNA
 DNA
is made up repeating units
called nucleotides
 Each nucleotide contains:



A phosphate molecule
A deoxyribose sugar
A base
Sugar-Phosphate Bond
THE DEOXYRIBOSE SUGAR
THE SUGAR-PHOSPHATE BACKBONE
 The
deoxyribose
Sugar contains 5
carbons
 The base is attached
to carbon 1
 The phosphate is
attached to carbon 5
 The phosphate of
the NEXT nucleotide
is attached to
carbon 3 by a
SUGAR-PHOSPHATE
BOND
DNA BASES
 In
DNA, there are 4 different
bases:
Base
 Therefore,
bases.
DNA has 4 different
What do you notice about the 2 strands?
COMPLEMENTARY BASE PAIRS
ADENINE
THYMINE
CYTOSINE
GUANINE
WEAK HYDROGEN BOND
ANTI-PARALLEL STRANDS

DNA is double stranded with the two strands
running in opposite directions. This is known as
an antiparallel arrangement.
5’
3’
3’
5’
DOUBLE HELIX
STRUCTURE OF DNA (SUMMARY)







DNA is made up repeating units called nucleotides
Each nucleotide contains:
 A phosphate molecule
 A deoxyribose sugar
 A base
There are 4 bases. Adenine pairs with Thymine and Guanine pairs
with Cytosine. This is known as complementary base pairing.
The two DNA strands are held together by weak hydrogen bonds
(between each of the bases)
The DNA strands have an antiparallel structure because the strands
run in opposite directions to each other
The DNA strand has 2 distinct ends: a phosphate group is at the 5’
end whereas the 3’ end is on the deoxyribose sugar
DNA has a sugar–phosphate backbone
 The deoxyribose sugar of the 1st nucleotide is joined onto the
phosphate molecule of the next nucleotide
 They are joined together by a strong sugar-phosphate bond
PROBLEM SOLVE!
1.
What is the correct sequence of bases to the
single DNA strand below?
2.
If a DNA molecule contained a total of 1000
bases and 400 were ADENINE bases, how many
bases of CYTOSINE would it contain?
400 Adenine = 400 Thymine
1000-800 = 200
200/2 = 100 guanine & 100 cytosine
HOW WAS ALL THIS DISCOVERED?
Your Task:

Your task is to research one of the individuals or
groups of scientists below whose work contributed
to the discovery of DNA structure and produce a
report on them:
WHAT TO INCLUDE:
 Griffiths
• Who the scientist(s) is, where
 Avery et al.
they worked and when
 Hershey and Chase
• The aims of the experiments
• What the experiments were,
 Chargaff
including a diagram
 Franklin and Wilkins
• What the conclusions were
 Watson and Crick
• other interesting information
that you have gathered that
lends interest to the story.
HOW WAS ALL THIS DISCOVERED?


Avery and Griffiths used bacterial transformation
experiments to change one form of bacteria to another
using the isolated DNA (they were not sure what the
mystery molecule was that had this effect) – See
animation here
Hershey and Chase used viruses called phage to
demonstrate that the molecule changing the bacteria was
DNA – See animation here

Erwin Chargaff worked out the base pair rule - See
animation here

Wilkins and Franklin used X ray crystallography to
investigate the structure of DNA – See animation here

Watson and Crick were the first to work the structure of
the double helix – See animation here
WHAT HAPPENS WHEN THE DNA
STRANDS HAVE BEEN FORMED?


Video: zoom in on the structure of chromosomes
and DNA
Video: How DNA is packaged
• DNA is tightly
coiled up
around 8
proteins
• These proteins
are called
Histones
• The
DNA/protein
‘bundle’ is called
a nucleosome
• Many
nucleosomes
make up a
chromosome
CHROMOSOME STRUCTURE

Chromosomes consist of tightly coiled DNA and
are packaged with associated proteins
QUESTIONS
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
What is the name given to the molecule inside cells that
controls inheritance of all features ?
What feature of the molecule contains the code controlling
inheritance of features?
Draw a single nucleotide and label the three component parts
Draw a second nucleotide and show how the two nucleotides
are joined to form part of the backbone and label the bond.
Explain the base pair rule
What type of bond holds the bases between opposite strands
together?
What name is given to the final shape of DNA?
The two strands of DNA run in opposite directions. What
name is given to this arrangement?
What special molecules are DNA packaged around?
What structures contain the all of the final DNA/protein
complexes?
STRUCTURE AND REPLICATION OF
DNA (A+B)



Describe the structure of DNA in terms of
nucleotides, backbone and complementary base
pairing
State how 2 DNA strands are held together
Describe the antiparallel structure of the DNA
strands

State where genetic information is stored
Define the term ‘genotype’
State what the genotype is determined by
State what the molecule of inheritance is

Describe the structure of a chromosome


