3.4.2 DNA and Protein Synthesis

Question 1

How do introns and exons affect protein synthesis?

Answer 1

Introns should not be transcribed or translated

Splicing is when exons are copied, introns are removed

Question 2

What is mRNA?

Answer 2

RNA that transfers the DNA code from the nucleus to the cytoplasm
Short for messenger RNA
Small enough to leave the nucleus though the nucleus pores and to enter the cytoplasm

Question 3

What is a codon?

Answer 3

A sequence of three bases on mRNA that codes for a single amino acids

Question 4

What is the genome?

Answer 4

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts

Question 5

What is the proteome?

Answer 5

The full range of proteins produced by the genome
Sometimes called the complete proteome, in which case the proteome refers to the proteins produced by a given type of cell under a certain set of conditions

Question 6

What is the structure of RNA?

Answer 6

Polymer made of repeating mononucleotide sub-units which forms a single strand
Nucleotide structure:
   Pentose sugar ribose
   One of the organic bases (A, G, C, U)
   A phosphate group

Question 7

What are the two types of RNA?

Answer 7

Messenger RNA (mRNA)
Transfer RNA (tRNA)

Question 8

What is the structure of mRNA?

Answer 8

Consists of thousands of mononucleotides
Long strand arranged into a single helix
Base sequence is determined by the base sequence of DNA in transcription

Question 9

What is the structure of tRNA?

Answer 9

Small molecule

See card

Question 10

What occurs during protein synthesis in terms of mRNA?

Answer 10

An anticodon pairs with the three complementary organic bases that make up the codon on mRNA

Question 11

What are the characteristics of DNA?

Answer 11

Double polynucleotide chain
Larger than mRNA and tRNA
Double helix
Pentose sugar is deoxyribose
Organic bases: A, G, C, T
Found mostly in the nucleus
Quantity is constant for all cells of a species except gametes
Chemically very stable

Question 12

What are the larger steps of protein synthesis?

Answer 12

DNA provides the instructions in the form of a long sequence of bases
Transcription: pre mRNA is formed
Splicing: Pre-mRNA is spliced to form mRNA
Translation: mRNA is used as a template

Question 13

What is transcription?

Answer 13

The process of making pre-mRNA using DNA as a template

Question 14

What are the steps of transcription?

Answer 14

DNA helicase breaks hydrogen bonds between the organic bases to expose the nucleotide bases
One strand acts as a template
The template pairs with complementary nucleotides present in the nucleus except A links to U
RNA polymerase moves along the strand and joins nucleotides together to form a pre-mRNA molecule
RNA polymerase adds nucleotides one at a time
DNA strands rejoin behind behind the pre-mRNA
When a stop code is reached by polymerase, it detaches and the pre-mRNA is formed

Question 15

What are the steps of splicing?

Answer 15

Pre-mRNA is spliced to form mRNA

Introns, which don’t code for proteins, are removed and the functional exons are joined together

Question 16

Do eukaryotic or prokaryotic cells undergo splicing?

Answer 16

Eukaryotic: contain introns so splicing is required
Prokaryotic: do not contain introns so splicing is unnecessary

Question 17

What is translation?

Answer 17

Translating codons on the mRNA into a sequence of amino acids to make up a polypeptide

Question 18

What is tRNA?

Answer 18

A molecule with a specific anticodon and attaches to a specific amino acid

Question 19

What are the steps of translation?

Answer 19

Ribosome becomes attached starting codon
tRNA molecule with complementary anticodon pairs up with the mRNA codon
Next codon is paired up with the complementary anticodon and so on
Each tRNA molecule carries an amino acid
Ribosome moves along the mRNA, forming one peptide bond at a time between amino acids
Any amino acids behind the ribosome have been joined and leave the tRNA molecule
The free tRNA molecule picks up another amino acid from the amino acid pool
This allows many chains to be produced at once
The polypeptide chain grows until a stop codon is reached and the chain seperates

Question 20

How is a protein produced from a polypeptide chain?

Answer 20

Polypeptide is folded to form the secondary structure
Secondary structure is folded to to produce the tertiary structure
Polypeptide chains are joined together to form a quaternary structure

Question 21

What is the role of ATP during translation?

Answer 21

Required to provide energy to attach amino acids to tRNA

To form peptide bonds between amino acids