storing and using genetic information

Question 1

define phenotype

Answer 1

outward, physical manifestation of organism

Question 2

define genotype

Answer 2

full heredity information of an organism

Question 3

what is protein structure ultimately dependent on

Answer 3

the primary structure of amino acids

Question 4

dna is a chain of …

Answer 4

nucleotide monomers

Question 5

what are the complementary base pairs

Answer 5

A-T/U

C-G

Question 6

what are some of the functions of the nucleus

Answer 6

• usually the largest organelle in the cell
• contain most of the cell’s genetic material
• replication of DNA and transcription occur here

Question 7

how is DNA packaged in the nucleus

Answer 7

packaged into chromosomes in a highly orderred manner

Question 8

define chromatin

Answer 8

the mixture of DNA, RNA and proteins that package DNA within the nu
can be heterochromatin or euchromatin

Question 9

how is chromatin made more accessible for transcription and replication

Answer 9

○ Histones can be enzymatically modified

• Histones can be displaced by chromatin remodelling complexes (no longer associated with histones)
• these processes are reversible

Question 10

define semi-conservative replication

Answer 10

one half of each new molecule of DNA is old, one half new

Question 11

explain bi-directional dna replication

Answer 11

• Replicated in the 5’ to 3’ direction
  DNA polymerase can only add new nucleotides to the 3’ end of the growing strand.
  Okazaki fragments are formed on the lagging strand which are joined together by DNA ligase to form one continuous strand. However the 5’ end of the lagging strand cannot be replicated in this way so a specialized enzyme – telomerase – replicates the 5’ ends of the lagging strand.

Question 12

how is DNA packaged during metaphase

Answer 12

• DNA is packed about 10 000 times more tightly in metaphase than in cells in other states - chromosomes are most compacted and visible during metaphase
• this allows an ordered 50:50 split when the chromosomes separate to allow normal functioning
• Achieved by repeatedly folding chromatin fibres into a hierarchy of multiple loops and coils

Question 13

what proportion of the genome is coding DNA

Answer 13

<2%
repeated sequences (Junk DNA) that are non-coding make up at least 50% of the human genome and it s important in regulating gene expression

Question 14

genetic code

Answer 14

describes how base sequences are coded into aa

Question 15

codon

Answer 15

set of 3 bases, codes for a particular aa

Question 16

describe the degenerate nature of the genetic code

Answer 16

there are 64 possible codons but only 20 aa

With the exception of methionine and tryptophan they are all encoded by more than one codon, this is referred to as degeneracy or the redundancy of the genetic code.
Codons which refer to the same amino acid are called synonyms and tend to be very similar. Variations between synonyms tend to occur at the third base of the codon – the wobble position.

Question 17

how does degeneracy minimise the effect of genetic mutation

Answer 17

alterations to the base sequences are less likely to alter the protein being coded for. This prevents any alteration in protein structure and hence function

Question 18

what is the function of RNA

Answer 18

participates in protein synthesis

Question 19

what is alternative splicing

Answer 19

process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing.
The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins.
Alternative splicing occurs as a normal phenomenon in eukaryotes, where it greatly increases the diversity of proteins that can be encoded by the genome

Question 20

reading frames

Answer 20

• Initiation codon determines the reading frame of the RNA sequence
• Usually only one reading frame contains useful information with others including a number of stop codons which will prevent the wrong protein being synthesised.
• A set of codons runs continuously and is bounded by a start/initiation codon and a termination codon – this is known as the open reading frame and is used to identify DNA which encodes protein sequences in genome sequencing projects.

Question 21

tRNA

Answer 21

• Major role is to translate mRNA sequence into aa sequence

Acts as an adaptor molecule between the coded aa and the mRNA

Question 22

rRNA

Answer 22

• Component of ribosomes
• rRNA molecules are produced in the nu
• Transported to cytoplasm, combine with proteins to form a ribosome
  Several ribosomes can translate mRNA at one time creating a polysome