View
248
Download
14
Category
Preview:
Citation preview
1 of 13 © Boardworks Ltd 2011
DNA
2 of 13 © Boardworks Ltd 2011
3 of 13 © Boardworks Ltd 2011
In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents.
What are chromosomes?
What makes this baby human? What determines her gender?
Chromosomes are located in the nuclei of cells.
4 of 13 © Boardworks Ltd 2011
Chromosomes are made of a molecule called DNA.
DNA molecules carry the code that controls what cells are made of and what they do.
DNA stands for deoxyribonucleic
acid.
Each chromosome is a very long molecule
of tightly-coiled DNA.
Which part of a DNA molecule holds this information?
What is DNA?
5 of 13 © Boardworks Ltd 2011
The structure of DNA
6 of 13 © Boardworks Ltd 2011
How do you think the four bases are paired?
DNA base pairs
There are four types of bases, and they are usually identified by their initials.
A
T
C
G
adenine
cytosine
guanine
thymine
The double helix ‘ladder’ of a DNA molecule is held together by ‘rungs’ made from pairs of chemicals called bases.
7 of 13 © Boardworks Ltd 2011
Base pairs hold the two strands of the DNA helix together.The rules for base pairing are…
There are millions of base pairs in a DNA molecule, and they always follow these rules.
‘A’ always pairs with ‘T’ ‘C’ always pairs with ‘G’
It is the sequence of these bases along a DNA molecule that forms the genetic code.
How do bases pair together?
A T C G
8 of 13 © Boardworks Ltd 2011
Determining the structure of DNA
The structure of DNA was determined in 1953 by James Watson and Francis Crick.
Previous X-ray studies by Rosalind Franklin and Maurice Wilkins had suggested that DNA was a double helix.
Erwin Chargraff had found evidence that DNA bases occurred in pairs.
These discoveries were not fully accepted until other scientists had performed their own tests and experiments.
9 of 13 © Boardworks Ltd 2011
Mapping the human genome
With the exception of identical twins, every human being has unique DNA. This means that individuals can be identified by a genetic ‘fingerprint’.
The Human Genome Project (HGP) was an international, publicly funded venture to sequence the three billion bases in the 20,000–25,000 genes of the human genome.
One of the subsidiary aims of the HGP was to address ethical and social concerns about how the information would be used. Can you think of any potential issues?
10 of 13 © Boardworks Ltd 2011
Genetic jargon
11 of 13 © Boardworks Ltd 2011
12 of 13 © Boardworks Ltd 2011
Glossary
13 of 13 © Boardworks Ltd 2011
Multiple-choice quiz
Recommended