The human genome

Question 1

What is the genome?

Answer 1

All the genetic information of an organism

Question 2

How many nucleotides making up coding genes in humans?

Answer 2

3.2 billion make up 20,000

Question 3

What is a genome divided up into?

Answer 3

2 sex chromosomes
44 (22 pairs) of autosomes
37 genes on circular mitochondrial chromosomes

Question 4

Why do mitochondria have their own separate set of genes?

Answer 4

13 out of 37 provide instructions for making enzymes

Question 5

What is a nucleotide made of?

Answer 5

Nitrogenous base
Phosphate group
5 carbon sugar (deoxyribose)

Question 6

What chemical bonds hold DNA together?

Answer 6

Covalent phosphodiester bonds between 5’ of one sugar and 3’ of another
Hydrogen bonds between base pairs

Question 7

How is DNA packaged into the nucleus?

Answer 7

1-DNA (negatively charged) bound to histone proteins (positively charged) to make nucleosomes
2-Coil nucleosomes to form 30nm thick
3-Chromatin fibres assembled on a protein scaffold to form a chromosome

Question 8

What is coding DNA?

Answer 8

codes for proteins

Question 9

7 examples of non coding DNA

Answer 9

Genes for other RNAs
Promoter regions
Introns
Tandem repeats
Telomeres
Pseudogenes
Viral DNA
Junk DNA

Question 10

What are Pseudogenes?

Answer 10

DNA sequence that resembles a gene but has been mutated into an inactive form over the course of evolution

Question 11

What are tandem repeats?

Answer 11

repeated short DNA sequences, occur due to polymerase “slippage”

Question 12

What is the role of coding RNA?

Answer 12

Messenger mRNA (DNA-mRNA and mRNA- proteins)
Viral genomes (RNA how some viruses store genetic material)

Question 13

What is the role of structural RNA?

Answer 13

Ribosomal rRNA (makes up ribosomes)
Transfer tRNA (carries amino acids to ribosome in translation)

Question 14

What is the role of regulatory RNA?

Answer 14

microRNA (involved in post- transcriptional regulation of gene expression)
Xist (switches off one copy of the X chromosome in XX cells creating a Barr body)

Question 15

What is the Sense/coding strand?

Answer 15

the stand (when read in the right direction) contains the specific code to make a protein, matches mRNA

Question 16

What is the Antisense/ template strand?

Answer 16

the stand with the opposite sequence to the sense strand

Question 17

Steps in DNA replication (leading strand)

Answer 17

• Unzip the double helix (DNA helicase)
• Attach a primer (primase enzyme)
• Add complementary nucleotides (DNA polymerase III adds nucleotides)

Question 18

What prevents over coiling?

Answer 18

Topoisomerase

Question 19

What direction are nucleotides added in?

Answer 19

5’ to 3’ direction and starts at primer

Question 20

Steps in DNA replication (lagging strand)

Answer 20

-Unzip
- Add primer (DNA polymerase only works in one direction so primer adds close to helicase)
- DNA polymerase III add nucleotides in 5’3’ direction
- Helicase unzips more and process repeats
- Once replication is complete= lagging strand is a mess

Question 21

What happens after DNA replication of the lagging strand?

Answer 21

• Made up of OKAZAKI FRAGMENTS
• Mix of RNA and DNA
• Primers from RNA are turned into to DNA using DNA polymerase I
• Gaps are stitched together by DNA ligase

Question 22

What is PCR?

Answer 22

• Amplifies a DNA sample in a lab to allow us to perform genetic testing

Question 23

What ingredients are added to PCR tube?

Answer 23

• The DNA sample from your patient
• Nucleotides
• Buffer solution
• Primers
• DNA Taq polymerase (heat stable DNA polymerase 1)

Question 24

Steps in PCR

Answer 24

• Denaturation (94-95)
• Annealing (50-60)
• Extension/ Elongation (72)
  Repeat approx 30 times, num of repeats depends on amount of DNA needed

Question 25

What is a Barr body?

Answer 25

An inactivated X chromsome in a female somatic cell

Question 26

What is the function of the enzyme DNA telomerase?

Answer 26

To prevent the ends of chromosomes from degradation

Question 27

What is semi conservative replication?

Answer 27

After replication each strand is made of half of the original strand