DNA,RNA and protein synthesis A

Question 1

what is the difference between the DNA stored in eukaryotes vs. prokaryotes

Answer 1

-Eukaryotic DNA= long,linear,associated with proteins called histones, tightly coiled into chromosomes
-Prokaryotic DNA= short, circular, not associated with histones

Question 2

name the protein associated with DNA in a chromosome

Answer 2

histone

Question 3

compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells

Answer 3

COMPARISONS
-nucleotide structure is identical
-nucleotides joined by phosphodiester bond
CONTRASTS
-eukaryotic DNA is longer
-eukaryotic DNA is linear and prokaryotic is circular
-eukaryotic DNA is associated with histones

Question 4

mitochondria and chloroplasts also contain ……… DNA like prokaryotic cells

Answer 4

circular

Question 5

what is a gene

Answer 5

section of DNA on a chromosome coding for one or more polypeptides

Question 6

What is the nature of the genetic code

Answer 6

-triplet code= sequence of three bases codes for a specific amino acid
-degenerate= more than one triplet codes for a single amino acid
-universal= same triplets code for the same amino acids in all living organisms
-non-overlapping= each triplet is read in sequence and bases are not shared between triplets

Question 7

what is an exon

Answer 7

exons are sequences of DNA within a gene that code for amino acids

Question 8

what are introns

Answer 8

introns are DNA sequences within a gene that don’t code for amino acids

Question 9

what are non-coding base sequences

Answer 9

-DNA that does not code for sequences of amino acids
-found between genes and at the end of chromosomes

Question 10

what are non coding repeats

Answer 10

DNA sequences found outside of genes that repeat over and over

Question 11

name two types of non-coding DNA

Answer 11

introns and repeats

Question 12

what name is given to a sequence of three DNA bases that codes for an amino acid

Answer 12

a triplet

Question 13

what is a genome

Answer 13

complete set of genes in a cell

Question 14

what is a proteome

Answer 14

the full range of different proteins that a cell is able to produce at a given time

Question 15

what are alleles

Answer 15

different version of the same gene

Question 16

what is a homologous pair of chromosomes

Answer 16

same size chromosomes with same genes, but different
alleles

Question 17

describe how a gene is a code for the production of a polypeptide

Answer 17

-because base/nucleotide sequence
-in a triplet
-determines order/sequence of amino acid sequence

Question 18

describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule

Answer 18

-condensation reaction
-between phosphate and deoxyribose
-catalysed by DNA polymerase

Question 19

not all mutations in nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why

Answer 19

-triplets code for same amino acid
-occurs in introns/ non-coding sequence

Question 20

name the type of bond between complementary base pairs

Answer 20

hydrogen

Question 21

name the type of bond between adjacent nucleotides in a DNA strand

Answer 21

phosphodiester

Question 22

what does the m in mRNA stand for

Answer 22

messenger

Question 23

what is an mRNA codon

Answer 23

an mRNA codon is a sequence of three mRNA bases that codes for amino acid

Question 24

what does t in tRNA stand for

Answer 24

transfer

Question 25

what are the differences between mRNA and tRNA

Answer 25

mRNA -single helix/straight -longer -contains no hydrogen bonds tRNA -folded into clover shape -shorter -contains hydrogen bonds

Question 26

what are the 2 stages of protein synthesis

Answer 26

1.transcription 2.translation

Question 27

what is transcription

Answer 27

-eukaryotes= transcribing DNA to pre-mRNA in the nucleus -prokaryotes=transcribing DNA to mRNA in cytoplasm

Question 28

what is splicing

Answer 28

-happens in eukaryotes only as prokaryotes do not have introns -introns are removed from pre-mRNA to form a strand of mRNA containing exons

Question 29

describe how mRNA is formed by transcription in eukaryotes

Answer 29

-hydrogen bonds between DNA bases break -only one DNA strand acts as a template -free RNA nucleotides align by complementary base pairing -uracil is used in place of thymine -RNA polymerase joins nucleotides -by phosphodiester bonds - pre-mRNA is spliced to form mRNA

Question 30

describe how mRNA is produced from an exposed template strand of DNA

Answer 30

-free RNA nucleotides form complementary base pairing -phosphodiester bonds form -by action of RNA polymerase

Question 31

in eukaryotic cells, the base sequence of mRNA might be different from the sequence of the pre-mRNA. explain why

Answer 31

-introns in pre-mRNA -removal of sections of pre-mRNA/ splicing

Question 32

describe the role of DNA helicase in eukaryotic transcription

Answer 32

-breaks hydrogen bonds between the two DNA strands in a gene -separates strands and allows DNA double helix to uncoil -allowing one strand to be used as a template -to produce complementary mRNA

Question 33

what is translation

Answer 33

-translating mRNA into a polypeptide -happens at the ribosomes

Question 34

describe how a polypeptide is formed by translation of mRNA

Answer 34

-mRNA attaches to ribosomes -tRNA anticodons bind to complementary mRNA codons -tRNA brings a specific amino acid -amino acids join by peptide bond -amino acids join with the use of ATP -tRNA released -the ribosome moves along the mRNA to form the polypeptide

Question 35

describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation

Answer 35

-tRNA brings specific amino acid to ribosome -anticodon on tRNA binds to codon on mRNA -amino acids join by condensation reaction using ATP

Question 36

what is the role of ATP in translation

Answer 36

● Hydrolysis of ATP to ADP + Pi releases energy ● So amino acids join to tRNAs and peptide bonds form between amino acids

Question 37

what is the role of tRNA in translation

Answer 37

● Attaches to / transports a specific amino acid, in relation to its anticodon ● tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds ● 2 tRNAs bring amino acids together so peptide bond can form

Question 38

what are anticodons and where are they found

Answer 38

-sequences of three bases found at the end of tRNA molecules -bind to complementary codons in mRNA