Chapter 4 - Protein Synthesis

Question 1

What is the genetic code?

Answer 1

• The specific order of nitrogen bases
• It is read by the cell and produces structural and functional proteins for use by the cell or the organism
• organised into genes and codes for a specific protein

Question 2

What is gene expression?

Answer 2

Reading one gene at a time. It is the process of using one genetic code to synthesise specific proteins.

Question 3

How are genes bundled together in prokaryotic cells and eukaryotic cells?

Answer 3

Prokaryotic cells - single circular chromosome
Eukaryotic cell - multiple linear chromosome

Question 4

What are the 3 stages of gene expression/protein synthesis?

Answer 4

• Transcription
• mRNA processing
• Translation

Question 5

What is transcription?

Answer 5

the process of synthesising a strand of mRNA that is complementary to the DNA base sequence of the gene being read

(makes a copy of a specific gene)

Question 6

Where does trandcription occur?

Answer 6

inside the nucleus before the mRNA leaves the nucleus

Question 7

What is the promoter region?

Answer 7

• Indicates the location on chromosome where gene starts
• not transcribed

Question 8

What is the template strand?

Answer 8

• Strand of the DNA that is transcribed
• All thymine bases will be replaced with uracil

Question 9

What are the 3 stages of transcription?

Answer 9

1. Initiation
2. Elongation
3. Termination

Question 10

What is transcription initiation?

Answer 10

• Transcription factors (proteins) bind to the promoter region. This helps RNA polymerase bind to the DNA
• RNA polymerase unwinds the DNA by breaking hydrogen bonds

Question 11

What is transcription elongation?

Answer 11

• RNA polymerase adds complementary nucleotides to the DNA
• Occurs from 5’ to 3’ direction

Question 12

What is transcription termination?

Answer 12

• RNA polymerase is released
• 2 strands of the DNA reanneal
• Single strand of the RNA peels off the DNA
• the RNA becomes the primary RNA transcript

Question 13

What is mRNA processing?

Answer 13

The primary RNA transcript is processed in the nucleus. It is modified in three ways before it leaves the nucleus.

Question 14

What are the 3 ways the RNA is modified in?

Answer 14

1. Caps and Tails
2. Splicing the gene
3. Reading the genetic code

Question 15

What is caps and tails?

Answer 15

5’ cap - a modified guanine nucleotide is added to 5’ end.

Poly-A tail - once the whole transcript has peeled f=off the DNA, 50-250 adenine nucleotides are added to 3’ end of RNA

Question 16

What types of sequence is the gene made up from?

Answer 16

Introns and exons

Question 17

What are introns?

Answer 17

non-coding regions that do not contribute to building proteins

Question 18

What are exons?

Answer 18

it is made up of coding sequences. genetic code within exons builds polypeptide.

Question 19

What is splicing the gene?

Answer 19

A complex of proteins and RNA molecules cut out all introns and stick the exons back together into a single mRNA sequence

Question 20

What is the reading the genetic code?

Answer 20

• reading the gene in sets of three bases.
  Triplet codes - codons (codes for a specific amino acid)

Question 21

What are stop codons?

Answer 21

Found at the end of the mRNA sequence
UAA, UAG, UGA

Question 22

What are start codons?

Answer 22

AUG - codes for methionin (MET)

Question 23

What happens before translation?

Answer 23

Mature mRNA moves out of the nucleus and into the cytoplasm

Question 24

What is translation?

Answer 24

The process of building a polypeptide chain using the mRNA as instructions

Question 24

Where does translation occur?

Answer 24

Occurs in the ribosome

Question 25

What are ribosomes made from

Answer 25

small and large subunit made from proteins and rRNA

Question 26

What are the 3 stages of translation?

Answer 26

1. Initiation 2. Elongation 3. Termination

Question 27

What is translation initiation?

Answer 27

- Small ribosomal subunit binds to 5' of mRNA and moves to start codon - A tRNA binds to mRNA - Large ribosomal subunit attaches to the complex

Question 28

What is translation elongation?

Answer 28

- A tRNA molecules with an inticodon complementary to the next mRNA codon enters ribosome - Each tRNA carries the amino acid coded for by the codon - The two amino acids bond together and the first tRNA molecule is released to fetch more amino acid molecules - mRNA moves through ribosome

Question 29

What is translation termination?

Answer 29

- Elongation continues until the stop codon moves through the chromosome - The polypeptide chain is released from the ribosome since the tRNA has a complementary anticodon

Question 30

What is an anticodon?

Answer 30

The triplet code found on tRNA that is complementary to mRNA sequence

Question 31

What is the coding region?

Answer 31

The section of the gene that is used to build the polypeptide chain

Question 32

What is a codon?

Answer 32

Three RNA bases in a row that code for a specific amino acid