DNA pt2, translation and transcription, and triplet codes

Question 1

Give 4 differences between prokaryotic and eukaryotic DNA

Answer 1

prokaryotic-
-short with fewer genes
-circular
-not associated with proteins
-no non-coding DNA

eukaryotic-
-long with many genes
-linear
associated with proteins called histones
-non-coding DNA is present

Question 2

What is a gene?

Answer 2

a base section of DNA that codes for the sequence of amino acids in a polypeptide chain

Question 3

What is an allele?

Answer 3

a different form of the same gene, found at the same locus on homologous chromosomes

Question 4

What is a locus?

Answer 4

a fixed position on a particular strand of DNA

Question 5

What is a trait of homologous pairs?

Answer 5

same genes, same length, potentially different alleles

Question 6

What is a karyotype?

Answer 6

an image of all chromosomes of an organism in a pair

Question 7

Each unique gene has…

Answer 7

a unique sequence of bases

Question 8

What does the unique sequence of bases determine?

Answer 8

the amino acid sequence in the polypeptide

Question 9

What could happen if there are differences in the base sequences of alleles of a single gene?

Answer 9

potentially a non-functional protein

Question 10

What is non-coding DNA?

Answer 10

DNA that does not code for polypeptides

Question 11

What are introns?

Answer 11

a section of eukaryotic DNA that does not code for amino acids

Question 12

What are exons?

Answer 12

a section of DNA that does code for amino acids

Question 13

What are multiple repeats?

Answer 13

a section of repetitive DNA formed outside of genes which does not code for amino acids

Question 14

Where else can DNA be found?

Answer 14

in chloroplasts and mitochondria

Question 15

What is a genome?

Answer 15

the complete set of genes in a cell

Question 16

What is a proteome?

Answer 16

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

Question 17

What are the two major processes involved in proteinsynthesis?

Answer 17

transcription and translation

Question 18

What is proteinsynthesis?

Answer 18

involves the production of a chain of amino acids that forms the primary structure of a protein

Question 19

What is splicing?

Answer 19

where the introns are removed by enzymes before the mRNA leaves the nucleus, just leaving the exons

Question 20

What is the role of ATP in proteinsynthesis?

Answer 20

IN TRANSLATION-
-attaching amino acids to the tRNA
-amino acids are joined by peptide bonds using an enzyme and ATP, which is hydrolysed to provide the required energy

Question 21

Explain what happens in transcription

Answer 21

-DNA helicase unwinds the DNA by catalysing the hydrolysis of the hydrogen bonds between the bases. one of these is used as the sense strand
-free RNA nucleotides in the nucleoplasm attach themselves to the sense strand by complementary base pairing. only one mRNA strand is made.
-the enzyme RNA polymerase join the nucleotides together
-mRNA strand detaches from sense strand, and the two original DNA strands join together again
-this pre-mRNA strand has lots of non-coding, junk DNA, so is spliced by the enzyme spliceosome, leaving a shorter, mature mRNA strand with only exons
-the mRNA diffuses out of the nucleus through a nuclear pore into the cytoplasm

Question 22

Explain the process of translation

Answer 22

-tRNA carry SPECIFIC amino acids to the mRNA
-a ribosome attaches to the mRNA at a start codon (AUG). the ribosome encloses two codons (6 amino acids)
-met-tRNA diffuses to the ribosome and attaches to the mRNA start codon by complementary base pairing
-the next amino acid tRNA attaches to the adjacent mRNA codon, by binding it’s anticodon to the codon
-the bond between the amino acid and the tRNA is cut, and instead a peptide bond is formed between the two amino acids, which requires an enzyme and ATP
-the ribosome moves along one codon so that a new amino acid tRNA can attach. the free tRNA molecule leaves to collect another amino acid. the cycle repeats from step 3
-the polypeptide chain is built up one amino acid at a time, folding up the protein as it goes, until a stop codon is reached

Question 23

What is the name for transcription and translation?

Answer 23

expression

Question 24

State the 3 properties of the genetic code

Answer 24

universal
degenerate
non-overlapping

Question 25

What does it mean by universal?

Answer 25

the same sequence of bases codes for the same amino acids in all organisms

Question 26

What does it mean by degenerate?

Answer 26

each amino acid is coded for by more than one triplet

Question 27

How do we know that you must read the genetic code in threes?

Answer 27

if it was in 1- only 4 possible amino acids

if it was in 2- only 16 possible amino acids

if it was in 3- 64 possible amino acids

and we know that there are 20 amino acids, so it must be in 3 because its the closest one with enough amino acids

Question 28

What does it mean by non-overlapping?

Answer 28

it is read in 3s- each base is only part of one triplet/codon

Question 29

What happens to a polypeptide chain after translation?

Answer 29

structural changes-
-amino acid chain is coiled/folded into secondary and tertiary structures

addition of a non-protein functional group

Question 30

Why are post-translational modifications necessary?

Answer 30

modifications of the primary structure give the protein it’s specific secondary and tertiary structure that allows it to perform it’s function