(8) DNA, RNA and protein synthesis

Question 1

describe the dna in eukaryotic cells (chromosomes)

Answer 1

it is long and linear, in the form of chromosomes, found in the nucleus
has to be wound up to fit in the nucleus- wound around proteins called histones

Question 2

how is the dna of mitochondria and chloroplasts in eukaryotic cells different to the normal dna

Answer 2

circular and shorter than nuclear dna (more similar to prokaryotic dna) and not associated with histone proteins

Question 3

what are the features of prokaryotic dna

Answer 3

dna molecules are shorter and circular, not wound around histones, it supercoils in order to fit into the cell

Question 4

define gene

Answer 4

a sequence of dna bases that codes for a polypeptide or functional RNA

Question 5

what forms the primary structure of the protein

Answer 5

the sequence of amino acids

Question 6

what is a triplet

Answer 6

a sequence of 3 bases in a gene

Question 7

what is a cells proteome

Answer 7

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

Question 8

what is functional RNA

Answer 8

RNA other than mRNA that perform special tasks during protein synthesis eg tRNA and ribosomal RNA

Question 9

what is an intron

Answer 9

sections that don’t code for amino acids within a gene

Question 10

what are exons

Answer 10

all the sections of the gene that do code for amino acids

Question 11

what is an allele

Answer 11

a different form of the same gene

Question 12

how does the blood type gene produce type O, type A and type B

Answer 12

the blood type gene exists as 3 different alleles and they all code for slightly different versions of the same polypeptide

Question 13

what is the function of mRNA

Answer 13

it carries the genetic code from the dna to the ribosomes where its used to make a protein during translation

Question 14

what is the function of tRNA

Answer 14

carries the amino acids that are used to make proteins to the ribosomes

Question 15

what is the structure of tRNA

Answer 15

single polynucleotide strand folded into a clover shape. hydrogen bonds between specific base pairs hold the molecule in this shape

Question 16

what happens during transcription

Answer 16

an mRNA copy of a gene is made from dna

Question 17

where does transcription take place in prokaryotic and eukaryotic cells

Answer 17

in eukaryotic cells it takes place in the nucleus

in prokaryotic in the cytoplasm

Question 18

what is pre-mRNA

Answer 18

mRNA strands containing introns and exons

Question 19

what is splicing

Answer 19

introns are removed from pre-mRNA and the exons join together forming strands of mRNA

Question 20

how is mRNA produced in prokaryotes

Answer 20

directly from DNA without splicing

Question 21

what are the 1st and 2nd stages of protein synthesis

Answer 21

1) transcription

2) translation

Question 22

what does it mean by the genetic code being non-overlapping

Answer 22

base triplets don’t share their bases, each triplet is separate from the triplet before it and after it

Question 23

what does it mean by the genetic code being degenerate

Answer 23

more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets) meaning some amino acids are coded for by more than one triplet

Question 24

what does it mean by the genetic code being universal

Answer 24

the same specific base triplets code for the same amino acids in all living things

Question 25

define what the genetic code is

Answer 25

sequence of base triplets (codons) in mRNA which code for specific amino acids

Question 26

what is a homologous pair in terms of chromosomes

Answer 26

2 chromosomes that carry the same genes but not necessarily the same alleles of the genes

Question 27

what is a codon

Answer 27

the sequence of three bases on mRNA that codes for a single amino acid

Question 28

how does the mRNA leave the nucleus in order to act as a template for protein synthesis

Answer 28

through pores in the nuclear membrane

Question 29

what is an anticodon

Answer 29

a sequence of 3 adjacent nucleotides on a molecule of tRNA that is complementary to a particular codon on a mRNA molecule

Question 30

what are the 5 steps of transcription

Answer 30

1) enzyme acts on a specific region of the dna causing the 2 strands to separate and expose the nucleotide bases 2) the nucleotide bases on one of the 2 dna strands is the template strand and pairs with the complementary nucleotides from the pool in the nucleus. RNA polymerase moves along the strand and joins the nucleotides to form pre mRNA 3) the complementary bases bind (adenine links to uracil) 4) as the rna polymerase adds nucleotides one at a time to build pre mRNA the dna strands rejoin behind it so only 12 base pairs on dna are exposed at a time 5) when the rna polymerase reaches a particular sequence of bases on the dna that is recognises as a stop codon, it detaches and pre mRNA is produced

Question 31

what does the emdosymbiotic theory state

Answer 31

a bacterial cell was engulfed by a larger cell. explains the presence of dna in mitochondria and chloroplasts

Question 32

what is symbiosis

Answer 32

after the cell was engulfed, the bacterial and host cell formed a beneficial symbiotic relationship

Question 33

what does dna in chloroplasts encode

Answer 33

the enzymes for photosynthesis

Question 34

describe the ancestors of mitochondria and chloroplasts

Answer 34

free living bacteria that needed their own dna to survive. when the bacteria became incorporated into a host cell some of the dna remained

Question 35

what 2 molecules make up ribosomes

Answer 35

RNA and protein

Question 36

during which phase of the cell cycle are gene mutations most likely to occur

Answer 36

interphase because it is the longest phase and is when gene replication occurs

Question 37

how is the structure of an mRNA molecule different to a tRNA molecule

Answer 37

mRNA doesn't contain hydrogen bonds/ base pairs | mRNA doesn't have an anticodon or an amino acid binding site all of which a tRNA molecule does have

Question 38

what is the difference between pre-mRNA and mRNA

Answer 38

pre-mRNA contains exons and introns but mRNA only contains exons

Question 39

why is it likely that the mRNA needed to produce one polypeptide is created more quickly in a prokaryotic cell than a eukaryotic cell

Answer 39

in eukaryotic cells the dna must be dissociated from histone proteins before transcription can take place (mRNA made) also the pre mRNA made during transcription has to undergo splicing but in prokaryotic cells the dna is not associated with histones and doesn’t contain introns so the production of mRNA takes less time