topic 7 : modern genetics

Question 1

what is a genome

Answer 1

all of the DNA of an organism including mitochondrial/chloroplast DNA

Question 2

what is the PCR used for

Answer 2

amplify DNA sample. used for dna sequencing and dna profiling

Question 3

what is DNA sequencing

Answer 3

determine nucleotide sequence

Question 4

what is DNA profiling

Answer 4

identifies unique sections of DNA to identify an individual

Question 5

How is PCR done

Answer 5

1. Reaction mixture contains: DNA sample, primers (short section of complementary DNA, its used as a starting point for the free nucleotides to then continue making the complementary chain), free nucleotides, Taq DNA polymerase (taken from organisms living in extreme heat environments so that the enzyme does not denature at high temp)
2. The mixture is heated 99C to break the H bonds between the complementary bases of the DNA (DNA unzips)
3. The mixture is then cooled 55C to allow the primers to join to the complementary section of the DNA – annealing
4. Mixture is heated again to 70C (optimum temp for Taq polymerase) for the phosphodiester bonds to form between the free nucleotides
5. This is repeated several times to produce many molecules of the DNA sample

Question 6

why is DNA sequencing used

Answer 6

used to predict the amino acid sequence and to determine the links between genetically connected individuals. This is done by gel electrophoresis

Question 7

How is DNA sequencing done

Answer 7

1. The sample of DNA is divided into four separate sequencing reactions. Each of the reactions contain the 4 standard nucleotides, DNA polymerase, primers and fluorescently labelled terminator nucleotides
2. The primers initiate the formation of complementary strands
3. Terminator nucleotides cause the replication to be terminated
4. As a result, several fragments of complementary strands are produced which are all different in size
5. Gel electrophoresis is used to separate the fragments
6. Fragments are viewed under UV light to enable the base sequence to be read

Question 8

what is DNA profiling used for

Answer 8

used for forensics to identify individuals and paternity testing

Question 9

how is dna profiling done

Answer 9

1. Fragments of DNA are cut by restriction enzymes
2. The fragments are separated using gel electrophoresis

Question 10

how is gel electrophoresis done

Answer 10

1. Fragments of DNA are placed in agar, and they are dyed with ethidium bromide so they are visible under UV light
2. DNA is negatively charged so it moves and is attracted towards the positive electrode at the end of the electrophoresis equipment
3. Fragments of DNA have different masses, so the lighter fragments move quicker and the heavier fragments move slower
4. This produces the appearance of various “bands” which can be analysed to identify the DNA sequence

Question 11

what is gene expression

Answer 11

The process by which a gene gets turned on in a cell to make RNA and proteins.

Question 12

what are transcription factors

Answer 12

proteins which bind to specific base sequences on DNA
- they sometimes initiate protein synthesis and other times they prevent protein synthesis

Question 13

what are promotor sequences

Answer 13

1. They are found upstream of the gene they act on
2. Enable the binding of RNA polymerase and hence promotes transcription

Question 14

what are enhancer sequences

Answer 14

1. Regulate DNA structure by changing the structure of chromatin
2. This allows/prevent RNA polymerase from binding
3. Open: gene expression is active, Closed: gene expression is inactive

Question 15

what is epigenetics

Answer 15

heritable and reversible modifications to the DNA that do not involve changes to the nucleotide sequence.

1. Study of changes in organisms due to the changes in gene expression rather than the change in the actual DNA code

Question 16

what is DNA methylation

Answer 16

when a Ch3 group is added to a CpG site (cytosine next to a guanine) on DNA. It prevents transcription and it has an effect on histone structure to make the DNA more/less accessible to RNA polymerase

Question 17

what is a histone protein

Answer 17

type of protein found in chromosomes. Histones bind to DNA, help give chromosomes their shape, and help control the activity of genes.

Question 18

what is histone modification

Answer 18

1. Methylation to cause the activation/inactivation of transcription
2. Acetylation: addition of a COCH3 group which allows transcription

Question 19

what is non-coding RNA

Answer 19

does not code for amino acids, but instead affects transcription or modifies the products of transcription

1. E.g. ncRNA coats an X chromosome which causes it to super coil and condense to become stable and inactive Barr body – this maintains the balance the products of genes

Question 20

what is RNA splicing

Answer 20

1. After transcription, the mRNA produced is immature: pre mRNA
2. Introns (non coding regions) are removed
3. The exons (coding regions) are joined together by an enzymes called spliceosomes
4. Mature mRNA is produced