gene expression

Question 1

4 structures

Answer 1

genes, triplet, codon, anticodon

Question 2

gene definiton

Answer 2

is a piece of DNA that codes for one specific protein

Question 3

triplet defintion

Answer 3

three consecutive bases on a DNA molecule, codes for an amino acid

Question 4

codon definition

Answer 4

three consecutive bases on a RNA molecule, codes for an amino

Question 5

anticodon definition

Answer 5

3 exposed bases on a tRNA molecule, complementary to a specific codon

Question 6

DNA strand in relation to mRNA

Answer 6

The DNA template strand is the strand that the mRNA is made from. It is complementary to the mRNA strand.

Question 7

mRNA strand

Answer 7

mRNA is “messenger” RNA and is the short single strand of RNA that is made off the template strand.

Question 8

tRNA strand in relation to mRNA

Answer 8

tRNA is “transfer” RNA that is complementary to the mRNA. Its anticodon ensures that the correct amino acid is added to the growing polypeptide chain

Question 9

transcription

Answer 9

The process where mRNA is made from the template strand of DNA in the nucleus. This process involves the DNA unwinding into two single strands.
An enzyme will then bind to the template strand of DNA at the promoter region. This enzyme will move along the DNA adding complementary RNA bases (A-U, C-G) until a terminating region is reached.
The completed strand of mRNA will now leave the nucleus. The two strands of DNA will bind back together. This is the end of transcription.

Question 10

translations

Answer 10

The process where the mRNA is read by the ribosome in the cytoplasm and an amino acid chain is created based on the codons on the mRNA.
This process involves the Ribosome binding to the start of the mRNA strand. The ribosome will move along the mRNA reading it in threes (codons).
tRNA, with three complementary bases (called anticodons) to the mRNA codons, will enter the ribosome and drop off their attached amino acid. The tRNA will then leave for another tRNA to enter the ribosome and drop off its amino acid.
These amino acids are joined together by the ribosome forming a polypeptide chain. This process continues until the ribosome encounters a stop codon. At this point the mRNA will leave the ribosome, the polypeptide chain will also detach. This is the end of translation.

Question 11

metabolic pathway definiton

Answer 11

is a series of linked biological reactions where the product of the first reaction is needed for the second reaction to proceed.

Question 12

mutation definiton

Answer 12

is a permanent change in the DNA\base sequence

Question 13

mutagen defintion

Answer 13

is an environmental factor that changes the DNA base sequence/increases the rate of mutations e.g ionising radiation, X-rays, alcohol, cigarette smoke, microorganisms etc. NOT just chemicals / toxins.

Question 14

metabolic pathway explantion

Answer 14

A gene is a section of DNA that codes for one protein / polypeptide chain.
Genes influence metabolic pathways because they code for the enzymes that catalyse the reactions in the pathway.
If a gene is mutated, this will mean that the resulting enzyme will not function and the end product can’t be made.
This is because the change/mutation in the DNA will result in the enzyme being a different shape/contain different amino acids

Question 15

point mutaion

Answer 15

Point mutation: one base is changed (can be a deletion, addition, or substitution)

Question 16

frameshift

Answer 16

caused by deletion and addition mutations - bases removed or added, causes all triplets downstream of mutation to change.

Question 17

substitution

Answer 17

one base in the gene is changed for another - can cause silent mutations (same-sense) due to degeneracy due to redundancy of the genetic code, usually less serious than other point mutations.

Question 18

effect of frameshift

Answer 18

A frame shift is where after a mutation, all the triplets are incorrect (as they are not “read” in their correct threes). Frame shifts can be deadly and are usually more serious than mutations that don’t result in frameshifts (can also result in STOP codons forming in the wrong place)

Question 19

phenotype definiton

Answer 19

is the physical expression of the genetic information in an organism’s DNA. The phenotype expressed is a combination of the genes an organism has AND the environment they are in.

Question 20

genotyope definiton

Answer 20

is the alleles that the thing possesses.

Question 21

environmental factor definiton

Answer 21

internal or external factor that affects the organism’s phenotype. It does not change the DNA sequence / does not affect genotype but alters the expression (transcription / translation) of genes

Question 22

effect of substitution

Answer 22

substitution (or a three base deletion / addition) will only (usually) affect one triplet / codon and therefore only one amino acid in the polypeptide chain.