Transcription and Translation

Question 1

what is the definition of transcription?

Answer 1

-the process of forming complementary copies of mRNA from sequences of DNA that code for a particular polypeptide

Question 2

what is the molecule that is involved in transcription?

Answer 2

-mRNA

Question 3

why does DNA always stay in the nucleus?

Answer 3

-less likely to be damaged in the nucleus than in the metabolically active cytoplasm

Question 4

what is the structure of mRNA?

Answer 4

-single strand
-shorter than DNA
-ribose pentose sugar
-uracil which replaces thymine

Question 5

what are the steps of transcription?

Answer 5

-DNA helicase separates the two strands of DNA by breaking the hydrogen bonds between base pairs
-RNA polymerase moves along the template strand and links the now exposed nucleotides with ribonucleotides from the nucleotide pool
-following base pairing rules
-the RNA polymerase then links the adjacent ribonucleotides together by phosphodiester bonds

Question 6

how many nucleotides are exposed at one time during transcription and why?

Answer 6

-because the unzipped DNA rejoins behind the assembly area

Question 7

when does transcription stop?

Answer 7

-when RNA polymerase reaches a stop codon it detaches and the copying of this polypeptide chain is finished

Question 8

what are the two sections called that DNA is made up of?

Answer 8

-exons and introns

Question 9

what are the jobs of exons and introns?

Answer 9

-exons are sections that code for a polypeptide and introns don’t

Question 10

do prokaryotic cells have introns?

Answer 10

-no they just have exons

Question 11

how is polypeptides modified to remove the intron and what is this process called?

Answer 11

-introns are removed from the pre RNA and the exons are spliced back together to produce as sequence that codes for the required polypeptide or protein

Question 12

what is the term given to the mRNA that contains introns?

Answer 12

-pre RNA

Question 13

what is the definition of translation?

Answer 13

-a process that involves the translation pf the mRNA code into the primary structure

Question 14

what is the term given to three bases on the mRNA strand that code for an amino acid?

Answer 14

-codon

Question 15

what are the two components that are involved in translation?

Answer 15

-tRNA and ribosomes

Question 16

what are some of the characteristics about tRNA? (4)

Answer 16

-single stranded
-clover leaf shaped
-have an anticodon which has complementary bases to the mRNA
-also have exposed nucleotides at the other end that can bind to amino acids

Question 17

how many different types of amino acids can tRNA attach to and why?

Answer 17

-only one due to their anticodon being specific to the type of bases on the amino acid

Question 18

what are the two roles of tRNA?

Answer 18

-transport amino acids to the site of protein synthesis
-ensure that each mRNA codon codes for a particular amino acid

Question 19

where are ribosomes found?

Answer 19

-in the cytoplasm free or attached to the RER

Question 20

what are the two sections of a ribosome and what are each of the ribosomes made up of?

Answer 20

-large and a small sub unit
-ribosomal RNA and protein

Question 21

where are the subunits of the ribosome assembled?

Answer 21

-in the nucleolus and are then transported into the cytoplasm

Question 22

what are the two sites on a ribosome that is concerned with translation and what are their jobs?

Answer 22

-the A site and the P site
-the A site is where tRNA molecules link together through linking the complementary codons and anticodons
-the p site is where adjacent amino acids are linked together by peptide bonds

Question 23

what is the process of translation?

Answer 23

-ribosome attaches to a start codon by its a site
-tRNA molecule attached to the codon via its complementary anticodon and attaches to its amino acid
-ribosome moves along the mRNA strand to accept another codon which links with the complementary anticodon on the tRNA again the tRNA is carrying its particular amino acid
-the first codon will now be in the p site and a peptide bond will be formed between the first two amino acids
-as the ribosome accepts another codon the tRNA for the first amino acid is set free
-another peptide bond is formed between the second and third amino acid
-this continues till a stop codon is reached

Question 24

where is the final place that polypeptides are processed and how does it occur?

Answer 24

-in the Golgi Apparatus
-proteins have to be processed before they are pinched off from the concave side of the Golgi
-they are then transported in vesicles to be used in or out of the cell