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 acidWhat 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 amino acids join together to form a protein molecule.

Each gene contains the sequence of bases for one protein.

The order of triplets in a gene determines the sequence of amino acids.

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.

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?

mutation

DNA mutations and proteins

A DNA mutation changes the amino acid sequenceand 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

DNA fingerprinting uses differences in DNA sequences to identify a specific individual. It is also known as genetic fingerprinting or DNA profiling.

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.

What is DNA fingerprinting?

How is DNA fingerprinting used?

DNA fingerprinting is also used for identifying criminals or victims of crime

DNA fingerprinting is currently used for identifying paternity or maternity

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 from crime scenes also can be compared to profiles stored in a database.

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.

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.

National DNA Database

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 DatabaseArguments 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.

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? 

National DNA Database

http://www.bbc.co.uk/learningzone/clips/dna-database-legal-or-illegal/8463.html

CGP Additional Science workbook pages 38-39 questions 2-5