Genome projects and making DNA fragments

Question 1

Define genome

Answer 1

The entire set of DNA in an organism

Question 2

What have improvements in technology allowed scientists to do?

Answer 2

Allows scientists to sequence the genomes of a variety of organisms

Question 3

When do gene fragments only work?

Answer 3

On fragments of DNA

Question 4

What did the Human Genome Project do?

Answer 4

It mapped the entire sequence of the human genome for the first time

Question 5

Define proteome

Answer 5

All the proteins made by an organism

Question 6

Why is it easy to determine the proteome from the DNA sequence of their genome in simple organisms?
How can this be useful?

Answer 6

They don’t have much non-coding DNA.
This can be useful in medical research and development

Question 7

Why is it harder to translate the genome into the proteome in complex organisms?

Answer 7

Complex organisms contain large sections of non-coding DNA.
They also contain complex regulatory genes which determine when the genes that code for a particular protein should be switched on and off.
It is harder to find the bits that code for proteins among the non-coding and regulatory DNA

Question 8

What were past sequencing methods like?

Answer 8

• labour intensive
• expensive
• could only be done on a small scale

Question 9

What are modern sequencing methods like?

Answer 9

• automated
• cost effective
• can be done on a large scale

Question 10

What does recombinant DNA technology involve?

Answer 10

Involves transferring a fragment of DNA from one organism to another

Question 11

What are trangenic organisms?

Answer 11

Organisms that contain transferred DNA

Question 12

What do your firstly need to do in order to transfer a gene from one organisms to another?

Answer 12

You need to get a DNA fragments containing the target gene

Question 13

Name the 3 ways to produce DNA fragments

Answer 13

1. Using reverse transcriptase
2. Using restriction endonuclease enzymes
3. Using a gene machine

Question 14

Explain how reverse transcriptase can be used to make DNA fragments

Answer 14

1. mRNA is easier to obtain from cells than DNA as they contain many mRNA molecules which are complementary to a gene.
2. the mRNA molecules can be used as a template to make lots of DNA. Reverse transcriptase makes DNA from an RNA template. The DNA produced is called complementary DNA (cDNA).
3. To do this mRNA is first isolated from cells. Then it is mixed with free DNA nucleotides and reverse transcriptase. The reverse transcriptase uses the mRNA as a template to synthesis a new strand of cDNA.

Question 15

Explain how restriction endonuclease enzymes can be used to make DNA fragments

Answer 15

1. Some sections of DNA have palindromic sequences of nucleotides which consist of anti-parallel base pairs
2. Restricting endonucleases are enzymes that recognise specific palindromic sequences (recognition sequences) and cut the DNA at these places
3. Different restriction endonucleases cut at different specific recognition sequences as the shape of the recognition sequence is complementary to enzyme’s activity
4. If recognition sequences are present at either side of the DNA fragment you want you can use restriction endonucleases to separate it from the rest of the DNA.
5. The DNA sample is incubated with the specific restriction endonuclease which cuts the DNA fragment out via a hydrolysis reaction
6. Sometimes the cut leaves sticky ends which can be used to bind the DNA fragments to another piece of DNA that has sticky end with complementary sequences

Question 16

What are sticky ends?

Answer 16

Small tails of unpaired bases

Question 17

Explain how a gene machine can be used to make DNA fragments

Answer 17

1. The sequence that is required is designed
2. The first nucleotide in the sequence is fixed to some sort of support
3. Nucleotides are added step by step in the correct order in a cycle of processes that includes adding protecting groups which makes sure that the nucleotides are joined at the right points to prevent unwanted branching.
4. Short sections of DNA called oligonucleotides (20 nucleotides long) are produced. Once these are complete they are broken off from the support and all the protecting groups are removed. The oligonucleotides can then be joined together to make longer DNA fragments.