Module 2 - Genetic information in cells

Question 1

What are the three stages of transcription?

Answer 1

Initiation, elongation, and termination

Question 2

What is the process of initiation during transcription?

Answer 2

Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.

Question 3

What is the process of elongation during transcription?

Answer 3

Transcription elongation is a regulated process in which an RNA chain complementary to the template strand of DNA is synthesized as RNA polymerase moves along DNA. The RNA transcript is nearly identical to the non-template, or coding, strand of DNA. However, RNA strands have the base uracil (U) in place of thymine (T), as well as a slightly different sugar in the nucleotide.

Transcription elongation is preceded by transcription initiation and is followed by transcription termination.

remember, eLONGation, the RNA strand gets LONGER

Question 4

What are RNA polymerase?

Answer 4

Enzymes that transcribe DNA into RNA.
Using a DNA template, RNA polymerase builds a new RNA molecule through base pairing. For instance, if there is a G in the DNA template, RNA polymerase will add a C to the new, growing RNA strand.
RNA polymerase always builds a new RNA strand in the 5’ to 3’ direction.

Question 5

What is the process of termination during transcription?

Answer 5

RNA polymerase will keep transcribing until it gets signals to stop. The process of ending transcription is called termination, and it happens once the polymerase transcribes a sequence of DNA known as a terminator.

After termination, transcription is finished.

Question 6

After termination (transcription), what happens?

Answer 6

The RNA transcript that was made is ready for translation. This RNA strand is called a messenger RNA (mRNA). The ribosomes will begin to translate the strand into a protein.
Ribosomes link amino acids together in the order specified by the codons of messenger RNA molecules to form polypeptide chains.

Question 7

What is the difference between RNA and DNA polymerase?

Answer 7

DNA polymerase is involved in DNA replication while RNA polymerase is involved in transcription.
Both involve the replication of DNA

Question 8

What is a promoter?

Answer 8

A promoter is a region of DNA where RNA polymerase begins to transcribe a gene. Normally, promoter sequences are typically located directly upstream or at the 5′ end of the transcription initiation site

Question 9

Is a primer needed for transcription? Why/why not?

Answer 9

No, RNA polymerase do not proofread their work, because it is a temporary molecule, and it doesn’t matter if there are a few mistakes.

Question 10

What is an intron?

Answer 10

It is an interruption in the coding sequence. They are cut out carefully by spliceosomes, then the exons are spliced together.

Question 11

What is an exon?

Answer 11

The expressed bits on the coding sequence

Question 12

What is a spliceosome?

Answer 12

The spliceosome is a large RNA-protein complex that catalyses the removal of introns from nuclear pre-mRNA. It will read messages, and recognise certain code words in the intron, then cut it out. Then the two exons will carefully join back together

Question 12

Compare and Contrast the process of RNA transcription and DNA replication

Answer 12

Features of Transcription:
- DNA strands are separated
- one strand is used as template
- monomer added sequentially at one end
- new polymer growth in 5’ to 3’ direction
- catalysed by RNA polymerase
- no helicase needed
- no primer needed

Features of DNA Replication:
- DNA strands are separated
- monomers added sequentially at one end
- new polymer growth in the 5’ to 3’ direction
- helicase is needed to separate double-stranded DNA into single strands, allowing each strand to be copied.
- primer is needed, as it provides a starting point for DNA synthesis.

Question 13

Where does transcription start?

Answer 13

At the Promoter, a specific binding site for RNA polymerase to begin transcription

Question 14

What codon initiates translation?

Answer 14

MET

Question 15

Why is the genetic code redundant?

Answer 15

Because there are two or more genes that perform the same function, and the inactivation of one of these genes can have little/no effect on the biological genotype.
This results in the effects of some mutations to be minimised.

Question 16

Describe a tRNA molecule and explain how its structure is related to its function

Answer 16

tRNA is the transfer RNA, that brings the correct amino acids to make up the polypeptide chain.
Its like a molecular interpreter.
Its structure is small, with many modified bases.
It has a 5’ and a 3’ end, and has base pairing with itself.
Amino acid attaches on top, while anticodon end is on the bottom.

Question 17

What is the function of an amino acyl - tRNA synthetase enzyme?

Answer 17

Aminoacyl-tRNA synthetases function is to attach amino acids to its tRNA.
They are enzymes that catalyze the aminoacylation reaction by covalently linking an amino acid to its cognate tRNA in the first step of protein translation.

Question 18

What is the relationship between the complementary sequences of codons and anti-codons?

Answer 18

Codons in the mRNA bind to the anticodons in the tRNA during protein synthesis (translation). This relationship ensures the correct the amino acids are added to the growing polypeptide chain.

Question 19

What is protein synthesis?

Answer 19

The process in which cells make proteins. It occurs in two stages: transcription and translation.

Question 20

What is a gene?

Answer 20

A section of DNA that carries the instructions for specific proteins or RNA molecules.

Question 22

What is a kinase and its function?

Answer 22

An enzyme that catalyses the transfer of a phosphate group from ATP to a specified molecule

Question 23

Define a gene

Answer 23

a section of DNA that carries the instructions for specific proteins or RNA molecules.

Question 24

Define a nucleosome

Answer 24

Nucleosome - a unit of DNA packaging in eukaryotes, consisting of DNA wound around eight histone protein

Question 25

Define a karyotype

Answer 25

a display of the chromosome pairs, arranged by size and shape

Question 26

Define a genome

Answer 26

the complete set of an organism’s genes and other DNA sequences

Question 27

What are euchromatin and heterochromatin

Answer 27

Euchromatin = loose chromatin that can be transcriptionally active. During the process of transcription there will be enzymes to bind to the DNA - that means that the DNA needs to be accessible

heterochromatin - tightly packed, and is transcriptionally inactive - meaning that the genes on the DNA are not accessible for enzymes to attach and interact with.

Question 28

what is a histone

Answer 28

a protein that provides structural support for a chromosome. In chromatin, there are eight histone proteins present

Question 29

what is chromatin

Answer 29

the complex of DNA and proteins (histones) that form the chromosomes that make up eukaryotic chromosomes

Question 30

What are haploids and diploids?

Answer 30

Haploid = one copy of chromosomes ( we have 46 chromosomes, two copies of every chromosome)
Diploid = two copies of chromosomes

Question 31

What direction does DNA polymerase add to?

Answer 31

At the 3’, and in the 5’ to 3’ direction

Question 32

What is a DNA helicase?

Answer 32

An enzyme that unwinds the DNA at the origin of replication

Question 33

What is a single stranded DNA binding protein?

Answer 33

A protein that prevents the two separated DNA strands from binding back together during replication

Question 34

What is topoisomerase?

Answer 34

An enzyme that relieves the tortional stress/ undoes the twisting of DNA

Question 35

What is the function of DNA polymerase?

Answer 35

Builds the DNA polymer in the 5’ to 3’ direction, starting at the RNA primer. Its also an enzyme that proof checks its work to make sure there are no mistakes in the nucleotides

Question 36

What is a primase?

Answer 36

An enzyme that makes a short RNA primer for the DNA polymerase to know where to start its replication process