Storing and using genetic info

Question 1

describe the double-helical structure of DNA

Answer 1

DNA is a chain of nucleotide monomers, each containing a sugar, base and phosphate group. The bases are stacked up, bound on the outside by the sugar-phosphate backbone. The two chains run anti-parallel to one another
one runs 3’ to 5’ and the other 5’ to 3’

Question 2

Describe how DNA forms chromosomes

Answer 2

DNA winds around histones

Question 3

How is DNA replicated?

Answer 3

special proteins (DNA helicase) 'unzip' the double helix by breaking the H bonds
DNA polymerase can only add new nucleotides to the 3' end of the growing strands. Fragments are formed on the lagging strand which are joined together by DNA ligase to form one continuous strand. Howevere, the 5' end of the lagging strand cannot be replicated in this way so a special enzyme 'telomerase' replicates the 5' ends of the lagging strand.

Question 4

Complementary base pairing

Answer 4

A-T

G-C

Question 5

structure of the nucleus

Answer 5

• contains most of the cell’s genetic material (DNA)

- DNA replication and first step of decoding it for protein take place here

Question 6

what does telomerase do?

Answer 6

replicates the 5’ ends of the lagging strand

Question 7

How is a base sequence of DNA transcribed into a base sequence of RNA

Answer 7

In the genome, each set of 3 bases is called a Codon. 
initiation codon (only has one possible codon sequence) tells enzymes where to begin the transcription of RNA
-from there, sequence is read in Codons until the Termination Codon is reached, which tells the enzymes to stop transcribing 
-Splicing of introns occurs leaving exons and produces a strand of mRNA 
at end- cap is added to 5' end and 3' end to protect it from being broken down by other enzymes

Question 8

Genotype

Answer 8

all the hereditory info of organism (even if it isn’t switched on or expressed)

Question 9

Major groove

Answer 9

most of the interactions with different molecules happen here i.e Transcription factor proteins

Question 10

Minor groove

Answer 10

too narrow for anything to fit in i.e proteins

Question 11

How is the physical shape of DNA molecule affected if base pairing is incorrect?

Answer 11

ie if A-C or G-T instead of A-T and G-C
as when bases pair correctly they fill a particular space, two sets of comp bases fit together well and enables DNA molecule to be packed tightly

Question 12

hydrogen bonds are easily…

Answer 12

broken down so can zip and unzip strands easily for DNA replication

Question 13

where is genetic material held?

Answer 13

most is in the nuclei but the rest is in the mitochondria as it has it’s own genome

Question 14

what is the nucleolus involved with?

Answer 14

making ribosomal RNA
this is important as if you didn’t make this then you wouldn’t have a fully functioning ribosome and so you couldn’t make protein

Question 15

Two reasons for highly ordered structure in chromosome?

Answer 15

• To pack everything in

- To allow regulation (by histones)

Question 16

Genetic testing:- banding pattern

Answer 16

dark banded patches- condensed parts of chromosome. Heterochromatin- less active, switched off, no gene expression produced

light patches- euchromatic-more active

Question 17

how are histones involved in regulating gene expression?

Answer 17

regulate the structure and function of nucleosomes
- Anything that makes nucleosomes more difficult to move will repress transcription, and ultimately down regulate the expression of the associated gene.

Question 18

DNA replication is described to be

Answer 18

semi-conservative- one half of each new molecule of DNA is old, one half is new

bi-directional- 5’ to 3’ direction, continuous and lagging strand however

Question 19

RNA splicing

Answer 19

removes non-coding regions of DNA (introns)

leaving only exons which go on to make protein

Question 20

What is a gene?

Answer 20

All the info that a cell needs to make a particular protein is contained in a sequence of DNA known as a gene.
-huge amount of variation can be produced
-each set of 3 bases is called a codon
each codon specifies a particular amino acid- only 20 amino acids though so more than one codon can refer to one amino acid

Question 21

Role of RNA

Answer 21

main role is to participate in protein synthesis

Question 22

mRNA

Answer 22

transcribed from DNA

carries info for protein synthesis

Question 23

alternative splicing

Answer 23

the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing.

Question 24

Methionine

Answer 24

only has one possible codon sequence so acts as the initiation codon and tells enzymes where to begin with the transcription of RNA

Question 25

Sequence is read in…

Answer 25

codons until the termination codon is reached, which tells enzymes to stop transcribing. Once this has occurred RNA splicing happens producing a stand of mRNA

Question 26

what happens once mRNA has been produced?

Answer 26

a cap is added to the 5’ end and a tail is added to the 3’ end to protect it from being broken down by other enzymes