Genetic Information and Relationships

Question 1

give the differences between prokaryotic and eukaryotic dna

Answer 1

prokaryotic:
circular, shorter than eukaryotic dna, not associated with histone proteins, doesn’t form chromosomes, sometimes in the form of plasmids, no introns

eukaryotic:
linear, longer than prokaryotic dna, associated with histone proteins, forms chromosomes, doesn’t have plasmids, contains introns

Question 2

why are dna strands described as antiparallel?

Answer 2

the dna base sequence is read one way on one strand and the other way on the other strand

Question 3

what is a gene?

Answer 3

a base sequence of dna that codes for the amino acid sequence of a polypeptide or a functional rna

Question 4

what is the gene locus?

Answer 4

fixed position on a particular dna molecule chromosome which a gene occupies

Question 5

what is the genome?

Answer 5

the complete set of genes in a cell

Question 6

what is the proteome?

Answer 6

the full range of proteins that a cell is able to produce

Question 7

what is a triplet?

Answer 7

3 bases in dna that code for amino acids

Question 8

what are non-coding multiple repeats?

Answer 8

dna base sequences between genes which don’t code for an amino acid

Question 9

what are exons?

Answer 9

dna base sequences within genes which code for an amino acid sequence

Question 10

what are introns?

Answer 10

dna base sequences within genes that don’t code for an amino acid sequence

Question 11

why is the genetic code described as universal?

Answer 11

in all organisms, each specific triplet codes for the same amino acid

Question 12

why is the genetic code described as non-overlapping?

Answer 12

each base is part of only one triplet

Question 13

why is the genetic code described as degenerate?

Answer 13

more than one triplet can code for the same amino acid

Question 14

why might there be more codes than there are amino acids?

Answer 14

if there’s a dna mutation, the amino acid sequence will be less likely to change so still get a functional protein

Question 15

why might the number of amino acids coded for be less than the number of triplets?

Answer 15

it may contain introns or a stop codon

Question 16

how can a dna mutation lead to a non-functional protein?

Answer 16

if there’s a mutation in the dna, this can sometimes change the amino acid sequence and protein primary structure. this might change the hydrogen, ionic and disulphide bond position in the protein, which changes the protein’s tertiary structure.
this can lead to a non-functioning protein

Question 17

give the similarities of a dna nucleotide and rna nucleotide

Answer 17

they both consist of a phosphate group, pentose sugar and a nitrogenous base

Question 18

give the differences of dna and rna

Answer 18

dna :
have deoxyribose sugar and adenine, thymine, guanine or cytosine as a base. a double helix, 2 polynucleotide strands

rna:
have ribose sugar, and adenine, URACIL, guanine or cytosine as a base. single helix, 1 polynucleotide strand

Question 19

what are the 3 types of rna?

Answer 19

mRNA, tRNA, rRNA

Question 20

what is the role of mRNA and where is it found?

Answer 20

it carries a template of the dna code for 1 gene to the ribosome for protein synthesis.
it is found in the cytoplasm

Question 21

what is the role of tRNA and where is it found?

Answer 21

it carries specific amino acids to the ribosome during protein synthesis.
it is found in the cytoplasm

Question 22

for both mRNA and tRNA, give the number of polynucleotide strands, the shape of the molecule, whether it has hydrogen bonds and amino acid binding site, the size of the molecule and what 3 bases are known as

Answer 22

mRNA:
1 polynucleotide strand, linear, no hydrogen bonds or amino acid binding site, longer than tRNA, 3 bases = codon

tRNA:
1 polynucleotide strand, clover leaf shape, has hydrogen bonds and amino acid binding site, shorter than mRNA, 3 bases = anticodon

Question 23

TAT CCA GTG CAC AGA
for this dna code, give the mRNA codons and the tRNA anticodons that would be complementary

Answer 23

mRNA codons:
AUA GGU CAC GUG UCU

tRNA codons:
UAU CCA GUG CAC AGA

Question 24

what are the 3 processes in protein synthesis?

Answer 24

transcription: the copying of the base sequence of a gene in dna onto the base sequence of a molecule of pre-mRNA, occurs in the nucleus

splicing: where introns from the pre-mRNA are removed to form mRNA

translation: the conversion of the base sequence of mRNA into the amino acid sequence of a polypeptide chain at the ribosome

Question 25

describe the process of transcription

Answer 25

1) an enzyme attaches to and unwinds the dna double helix to be transcribed- hydrogen bonds between the 2 strands are broken causing the strands to separate
2) one strand is used as a template
3) free rna nucleotides bind with exposed dna bases via complementary base pairing- uracil to adenine, adenine to thymine, cytosine to guanine, guanine to cytosine
4) the enzyme rna polymerase joins the adjacent rna nucleotides forming phosphodiester bonds and pre-mRNA
5) the introns in the pre-mRNA are removed through splicing, leaving a molecule of mRNA.
6) the mRNA passes out of the nucleus via nuclear pore and goes to the ribosome

Question 26

how does transcription differ in prokaryotes and eukaryotes?

Answer 26

splicing doesn’t occur in prokaryotes because prokaryotic dna doesn’t contain introns

Question 27

describe the process of translation

Answer 27

1) mRNA attaches to the ribosome and moves along to find the start codon
2) 2 codons fit into the ribosome at one time
3) tRNA carrying a specific amino acid binds to the start codon on the mRNA via complementary base pairing- uracil to adenine, adenine to thymine, cytosine to guanine, guanine to cytosine
4) a second tRNA carrying a specific amino acid binds to the 2nd codon on mRNA, via complementary base pairing with its anticodon
5) enzymes join the amino acids together forming peptide bonds, using energy from the hydrolysis of atp
6) the ribosome moves to the next codon, and the tRNA is removed from the first codon, which goes to collect the same amino acid from the cytoplasm
7) another tRNA carrying a specific amino acid binds to the 3rd mRNA codon, via complementary base pairing and a new peptide bond forms between the amino acids
8) this process repeats until the stop codon is reached and the polypeptide detaches from the ribosome

Question 28

what is an allele?

Answer 28

different forms of the same gene

Question 29

what are homologous chromosomes?

Answer 29

a pair of chromosomes which have the same genes at the same gene loci but may have different alleles

Question 30

what is a haploid cell?

Answer 30

a cell containing one of each type of chromosome eg a gamete

Question 31

what is a diploid cell?

Answer 31

a cell containing two of each type of chromosome eg a normal body cell (or somatic cell)

Question 32

what is the definition of sexual reproduction?

Answer 32

when 2 gametes join to make a zygote of a new organism, the joining of gametes is called fertilisation.

Question 33

what is a gene mutation and when do they arise?

Answer 33

a change in the dna base sequence of a chromosome that results in the formation of a new allele.
they arise spontaneously during dna replication.

Question 34

what is a substitution mutation?

Answer 34

where one dna base is replaced with a different base

Question 35

sometimes when a substitution happens, the same amino acids can be made, why?

Answer 35

due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids, so the tertiary structure of the protein stays the same

Question 36

what is a deletion mutation?

Answer 36

where one dna base is removed from the dna base sequence

Question 37

what does a deletion mutation cause?

Answer 37

a frameshift in the dna base sequence which changes the triplets from the point of mutation

Question 38

how does a deletion mutation affect the amino acid sequence and the rest of the protein?

Answer 38

deletion mutations cause a frameshift in the dna base sequence so different amino acids are coded for. this would affect the position of hydrogen, ionic and disulphide bonds which would change the tertiary structure of the protein and the shape of the protein. this can lead to it becoming non-functional.

Question 39

what is a mutagenic agent + examples?

Answer 39

something that increases the rate of gene mutations
examples:
uv radiation
ionising radiation ( x-rays, gamma rays)
carcinogens (asbestos, tobacco tar from cigarettes)
chemicals (benzene, caffeine)