Biology - Review Qns - 3.1

Question 1

Nucleic acids

Answer 1

Polymers of nucleotides

Polynucleotides

There are two types of nucleic acids: DNA and RNA

Question 2

Purines

2 examples

Answer 2

Nitrogenous Bases

Adenine

Guanine

Question 3

Pyrimidines

Answer 3

Cytosine

Thymine

Uracil

Question 4

Forming polynucleotides

Answer 4

Nucleotides are joined in a condensation polymerisation reaction to form polynucleotides.

Water is released and a covalent bond (phosphodiester bond) forms joining the nucleotides together.

Question 5

Describe

DNA

4 Points

Answer 5

Long

Coiled

Double-stranded nucleic acid

It forms a double helix.

The two strands of DNA are antiparallel. One runs in the 5’ to 3’ direction, while the other runs in the opposite direction.

Question 6

How are DNA nucleotides built

Answer 6

Nucleotides are made up of

• Deoxyribose sugar
• Phosphate
• One of four nitrogenous bases (adenine, cytosine, guanine and thymine).

The two strands of DNA are joined by complementary base pairing between the nitrogenous bases.

Question 7

Describe

RNA

3 points

Answer 7

Short

Usually single-stranded

Nucleic acid

Question 8

RNA construction

Answer 8

RNA contains nucleotides that are made up of

• Ribose sugar
• A phosphate
• one of four nitrogenous bases (adenine, cytosine, guanine and uracil).

Question 9

DNA role

Answer 9

DNA stores hereditary information

Carrys the instructions that code for the production of mainly proteins but also functional RNA molecules

It is stored in a specific sequence of nucleotides.

Question 10

Definition

Gene

Answer 10

A gene is a region of DNA that codes for a protein or a functional RNA molecule

Question 11

The role of RNA

Answer 11

To express the information contained in the nucleotide sequence of a gene to synthesise proteins

Question 12

Definition

mRNA

Answer 12

A single-stranded nucleic acid that carries a copy of the genetic sequence in DNA, specifying the amino acid sequence for a particular protein.

Question 13

rRNA

Answer 13

Makes up part of a ribosome. Ribosomes are the sites where the information in the mRNA is translated into a chain of amino acids.

Question 14

Definition

tRNAs

Answer 14

Carry specific amino acids to ribosomes in order to form polypeptide chains

Question 15

Term to describe these:

Nitrogenous Bases

Adenine

Guanine

Answer 15

Purines

2 examples

Question 16

Term to describe these:

Cytosine

Thymine

Uracil

Answer 16

Pyrimidines

Question 17

What is

The geneic code

Answer 17

the genetic code is the set of rules about how the instructions carried in nucleic acids are translated to synthesise proteins and functional RNA molecules.

Question 18

How is the genetic code stored

Answer 18

In DNA this information is stored as a three-letter code of nucleotides known as a triplet.

Question 19

What are codons?

Answer 19

When these triplets are transcribed into mature mRNA, they are then known as codons.

Question 20

Key points

Genetic Code

Answer 20

The genetic code is universal and degenerate. There are 64 possible codons of three nucleotides (e.g. UAC) for the 20 amino acids.

Question 21

Common Features

Eukaryote genes

4 points

Answer 21

Eukaryotic genes have a number of structural features in common:

• Stop and start instructions —These indicate where transcription starts and stops. Stop codons do not code for amino acids.
• Promoter region—This is the site at which the RNA polymerase attaches to the gene to begin transcription (sometimes called the TATA box).
• Exons—These are the DNA regions that are coding segments.
• Introns—These are the DNA regions that are non-coding segments

Question 22

What is gene expression?

Answer 22

Gene expression is the process in which the information stored in a gene is used to synthesise a functional gene product (protein or RNA). Gene expression is regulated so that it occurs if and when the particular protein or RNA is required by the cell.

Question 23

What are the Eukaryote protein synthesis stages?

Answer 23

Protein synthesis in eukaryotes occurs in three stages:

• transcription
• RNA processing
• translation.

Question 24

Describe

Eukaryote protein synthesis - Transcription

3 steps & 2 points

Answer 24

Transcription occurs in the nucleus and involves RNA polymerase transcribing the DNA into a primary RNA transcript.

• During RNA processing in eukaryotes, a 5’ cap is added to the 5’ end of the primary RNA transcript and a poly
• A tail is added to the 3’ end.

The cap and tail make the mRNA more stable and prevent it from degrading.

• Next, the primary RNA transcript is spliced to remove the introns, and someti mes some exons, resulting in mature mRNA.
• The mature mRNA then exits the nucleus.

Question 25

Describe **Eukaryote protein synthesis - Translation** 3 steps

Answer 25

Translation occurs on a ribosome.The codons on mRNA are translated into a sequence of amino acidsThese are delivered by their specifc tRNA molecules, to form a polypeptide chain.

Question 26

**When can Eukaryote gene expresion be regulated**

Answer 26

Gene expression in eukaryotes can be regulated at any of the three stages: transcription, RNA processing and translation.

Question 27

**When can Prokaryote gene expresion be regulated**

Answer 27

Gene regulation in prokaryotes occurs during transcription.

Question 28

**When are Constitutive genes expressed**

Answer 28

Constitutive genes are expressed continually.

Question 29

Define ## Footnote **Transcription factors**

Answer 29

Transcription of other genes can be induced or repressed as needed by transcription factors, which is a form of gene regulation.

Question 30

Define ## Footnote **Regulatory genes**

Answer 30

Regulatory genes code for the production of transcription factors.

Question 31

Define **Transcription factors** Their working method

Answer 31

Transcription factors are proteins that control gene expression at the transcription stage. They induce or repress the expression of specifc genes by binding to DNA sequences close to the promoter region of a gene or to the RNA polymerase.

Question 32

Define ## Footnote **Structural genes**

Answer 32

Structural genes code for proteins and RNAs that are not involved in gene regulation; for example, enzymes.

Question 33

**E coli example of transcription regulation**

Answer 33

The 'lac operon' in E. coli provides an example of a unit of DNA for which transcription can be induced or repressed—or in other words, regulated. - The regulatory gene lacI constitutively expresses a transcription factor called the lac repressor. - The lac repressor binds to the operator of the lac operon, inhibiting transcription, unless lactose is present. - In the presence of lactose, the lactose binds to the lac repressor, inhibiting it from binding to the lac operon, and enabling the RNA polymerase to bind to the lac operon and begin transcription.

Question 34

**Contrast structure of genetic info between prokaryotes and eukaryotes**

Answer 34

There are many diferences in the structure of the genetic information of prokaryotes and eukaryotes, - Prokaryotes have much less DNA but more genes per number of bases than eukaryotes. - Because eukaryotes have much more DNA, they have to package it more tightly. - These structural diferences afect the way in which genetic information is transcribed, translated and expressed.

Question 35

**Similarities of genetic info in prokaryotes and eukaryotes.**

Answer 35

The same code of nitrogenous bases (A, T, C, G and U) translates into amino acids and proteins in much the same way in prokaryotes and eukaryotes