Biological molecules - how does DNA code for proteins?

Question 1

How does genetic coding, sitting in the nucleus get to code proteins which float in the cytoplasm? (3pts)

Answer 1

1. Transcription:
2. a copy of the gene coding required is made from RNA
3. RNA can leave the nucleus carrying the ‘info’ for correct protein synthesis in the cytoplasm

Question 2

What is RNA and how is it different from DNA?

Answer 2

1. ribonucleic acid
2. similar to DNA but contain ribose not deoxyribose
3. and uracil replaces thymine

Question 3

What does mRNA mean?

What does it do?

Answer 3

Messenger RNA

Directs the synthesis of a protein

Question 4

What does rRNA mean? What does it do?

Answer 4

Ribosomal RNA

Joins ribosomal proteins to make ribosomes

Question 5

What does tRNA mean? What does it do?

Answer 5

Transfer RNA

tRNA binds to an amino acid in the cytoplasm

it holds it in place on a ribosome until it is incorporated into a protein during translation

Question 6

Explain how tRNA works..

Answer 6

one end of tRNA carries a specific amino acid,

the opposite end has a triplet of nucleotides - an anticodon

complementary bases then pair up, the tRNA anticodon attaches to the mRNA codon

there are 20 different tRNA types and they bind to only one of the 20 amino acids.

Question 7

What does RNA polymerase do?

Answer 7

RNA polymerase catalyzes transcription of DNA

Question 8

What is the sequence of RNA in transcription to protein synthesis? (2 pts)

Answer 8

1. RNA is made in the nucleus by transcription (copying) - it is called mRNA (or messenger RNA) as it carries the coding outside of the nucleus
2. the second stage is called tanslation which involves transfer RNA (tRNA) and ribosomal RNA (rRNA)

Question 9

Explain the sequence of transcription (7 pts)

Answer 9

INITIATION

RNA polymerase attaches to DNA, breaking its hydrogen bonds can causing it to unwind and to start the copying of part of the DNA required - it starts ‘reading’ at a certain part and ends at another part (just like reading two paragraphs in a chapter)

One of the DNA strands, the template, is transcribed (copied) for the required protein to create mRNA

ELONGATION

the mRNA is ‘edited’ as other completmentary base nucleotides are added creating a full mRNA

TERMINATION

at the end of the transcription, the RNA polymerase enzyme reaches a terminator/stop sequence (‘end of the paragraph’) and the mRNA detatches.

the DNA zips back up completing the sequence

Question 10

What is translation in this context?

Answer 10

Turning the sequence of bases in the genetic code into a sequence of amino acids

Question 11

What is the nature of the genetic code

Answer 11

Four bases, but these four bases need to create 20 amino acids

The code carried by DNA is triplet code

There are thus 64 possible combinations of each codon (4 bases raised to 3rd power, 4³ = 64)

Question 12

What does ‘degenerate’ mean in DNA coding?

Answer 12

several triplet codes can code for the same amino acid

Question 13

What is the relationship between codons and amino acids?

Answer 13

Each codon on mRNA corresponds to (practically) different amino acids.

EG

UUU = phynenylalanine

UUA = leucine

CAG = glutamine

GGG = glycine

Question 14

Once out of the nucleus, what does mRNA attach to?

Answer 14

The mRNA attaches to a ribosome (these float around the cytoplasm or are found hanging out at the endoplasmic reticulum pub)

Ribosomes have a larger and smaller subunit;

1) mRNA attaches to the smaller ribosome unit
2) the larger contains two tRNA binding sites which face two mRNA codons

Question 15

How do 30,000 human genes code for between 1/2 million and a million proteins?

Answer 15

Alternate splicing of mRNA which creates leverage

pre-mRNA transcribed from a gene is spliced in different ways to produce several different mRNAs

these different mRNAs are translated into different proteins

that way, one gene may code for 10+ different proteins

(also, when proteins go through the Golgi complex, they can be altered)