Download DNA & Proteins

DNA & Proteins
B3a
OBJECTIVES
Grade D-C
 Describe the link between DNA and proteins.
Grade B-A*
 Explain how protein structure is linked to DNA
 Explain what transamination is and where it
occurs.
 Explain how proteins are ‘designed’ for a specific
function.
Label the diagram
What are proteins made of?
Proteins are long molecules made from chemical units
called amino acids.
protein
molecule
amino acid
What happens if amino acids are combined in a different
order?
Different combinations of amino acids make different proteins.
Connecting proteins and genes
Consider the following two statements…
Genes carry the
instructions for
inherited characteristics.
Cells have different
characteristics because
they make different
types of proteins.
What is the connection between genes and proteins?
Genes contain the instructions
for making proteins.
What molecule has the instructions for making proteins?
How do genes make proteins?
Genes are made of DNA. Proteins are made of amino acids.
Each amino acid is coded for by its own special sequence
of three bases called a triplet:
triplet
amino acid
How do genes make proteins?
The order of triplets in a gene determines the sequence
of amino acids.
The amino acids join together to form a protein molecule.
Each gene contains the sequence of bases for one protein.
Why is the sequence of bases in DNA called the genetic code?
How do genes make proteins?
The genetic code is the order of DNA bases which
determines the sequence of amino acids in a protein.
How many triplets code for a protein of 20 amino acids?
1 amino acid = 1 triplet
20 amino acids = 20 triplets
How many bases code for a protein of 20 amino acids?
Build your own protein molecule
DNA mutations and proteins
A mutation is a change in the sequence of bases in DNA.
mutation
Mutations can be caused by mistakes in copying DNA
or the effects of radiation and heavy metal ions.
Will the mutated version of DNA make the same protein?
DNA mutations and proteins
A DNA mutation changes the amino acid sequence
and so a different protein may be produced.
If genes produce incorrect proteins, cells may not function
properly. This is the cause of many inherited diseases.
Genetic code quiz
DNA Fingerprinting
What is DNA fingerprinting?
The chemical structure of
everyone's DNA is the same the only difference is the order of
the base pairs. There are so
many millions of base pairs in
each person's DNA that every
person has a different sequence.
DNA fingerprinting uses
differences in DNA sequences to
identify a specific individual. It is
also known as genetic
fingerprinting or DNA profiling.
How is DNA fingerprinting used?
DNA
fingerprinting
is currently
used for
identifying
paternity or
maternity
DNA fingerprinting is also
used for identifying criminals
or victims of crime
How it works
 Only 0.1% of DNA (about 3 million bases) differs from one
person to the next. These different regions are used to generate
a DNA profile of an individual, using samples from blood, bone,
hair, and other body tissues and products.
 Enzymes are used to cut out
specific sequences of DNA. The
different lengths are then
arranged in order of length
using electrophoresis
 Once the DNA sequences are
ordered, they are labelled so
that they show up when
photographed. This produces
the 'fingerprint' - a series of
black lines corresponding to the
DNA sequences present.
How it works
 In criminal cases, DNA samples from crime-scene evidence
and a suspect are compared. If the sample profiles don't match,
the person did not contribute the DNA at the crime scene.
 If the patterns match, the suspect may have contributed the
evidence sample.
DNA collected at the
scene of a crime is
compared with DNA
samples collected from 4
possible suspects. The
fragments from suspect 3
match those left at the
scene of the crime,
betraying the guilty party.
 DNA from crime scenes also can be compared to profiles
stored in a database.
National DNA Database
 Britain has the largest DNA
database of its citizens in the
world. It holds details of over 4
million people – 5.2% of the UK
population is on the database
compared with 0.5% in the USA.
 DNA samples obtained for analysis from the collection of
DNA at crime scenes and from samples taken from
individuals in police custody can be held in the national
DNA database.
 These include people who have been found guilty of a
crime as well as those suspected of a crime but eventually
cleared.
National DNA Database
Arguments in favour
 Each person's DNA is unique (with the exception of identical
twins). Therefore, DNA evidence collected from a crime scene
can implicate or eliminate a suspect, similar to the use of
fingerprints.
 It also can analyse unidentified remains through comparisons
with DNA from relatives.
 When evidence from one crime scene is compared with
evidence from another, those crime scenes can be linked to
the same perpetrator, helping to solve crimes
 When biological evidence from crime scenes is collected and
stored properly, forensically valuable DNA can be found on
evidence that may be decades old. Therefore, old cases that
were previously thought unsolvable may contain valuable DNA
evidence capable of identifying the perpetrator.
National DNA Database
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Arguments against
It is possible for an innocent person’s DNA to be planted at a
crime scene, either to mislead police or to incriminate an enemy
of the real perpetrator.
An innocent person’s DNA may also be at a crime scene even
though they were not involved in the crime – e.g. hair being
transferred on clothing
Cost: maintaining and developing the database required
government and police investment of over £300million over the
last five years.
It would invade our right to privacy.
The data might get into the hands of commercial companies
such as insurance, loan and employers. If it could be used to
identify that you had a genetic risk for a serious disease, could
you find yourself refused life insurance, a loan, or even a job?
http://www.bbc.co.uk/learningzone/clips/dna-database-legal-or-illegal/8463.html
CGP Additional Science workbook
pages 38-39 questions 2-5