Topic 3: Genetics

Question 1

What is DNA?

Answer 1

• DNA is genetic information for an organism.
• It is passed from parents to offspring
• Stands for Deoxyribonucleic Acid.

Question 2

Where is DNA in a cell?

Answer 2

In the nucleus

Question 3

What is the structure of DNA?

Answer 3

• DNA is shaped like a twisted ladder (double helix)

Question 4

Definition of a chromosome?

Answer 4

• Tiny threads that are made of DNA
• The shape DNA takes when it is coiled up

Question 5

Definition of a gene?

Answer 5

• A gene is a segment of DNA that codes for a specific protein

Question 6

Describe the relationship between
chromosomes, DNA and genes?

Answer 6

• There are 46 chromosomes inside a human nucleus
• Chromosomes are made up of DNA
• Chromosomes contain genes that determine the traits of an organism

Question 7

What is a nucleotide?

Answer 7

• The basic building block of DNA
• Nucleotides are made up of a phosphate group, a deoxyribose sugar and a nitrogenous base

Question 8

What are the 4 bases in DNA? What base
pairs with what?

Answer 8

DNA has four different bases:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
- Nucleotides are joined together by their sugar-phosphate groups.
A pairs with T
G pairs with C
T pairs with A
C pairs with G

Question 9

What bonds hold together the bases in DNA?

Answer 9

• Hydrogen bonds hold together the nitrogenous bases.

Question 10

What is RNA?

Answer 10

• A ribonucleic acid, that is present in all living cells. Its main role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins.
• Divided into 3 types (mRNA, rRNA, tRNA)

Question 11

List the differences between DNA and RNA?

Answer 11

1. DNA is double-stranded, RNA is single-stranded
2. DNA has a deoxyribose sugar, RNA has a ribose sugar.
3. DNA uses Thymine (A), RNA uses Uracil (A)
4. DNA is located in the nucleus, RNA is located in the nucleus and cytoplasm.

Question 12

What pairs with adenine (mRNA)?

Answer 12

Uracil

Question 13

Similarities between DNA and RNA

Answer 13

• Uses Guanine, Cytosine, and Adenine
• Has a sugar-phosphate backbone.

Question 14

What is protein synthesis?

Answer 14

The process in which cells make proteins through transcription and translation

Question 15

What are the 2 steps of protein
synthesis?

Answer 15

Protein synthesis involves 2 important steps:
Transcription (DNA → mRNA)
Translation (mRNA → protein)

Question 16

What happens during transcription?

Answer 16

• DNA to mRNA
• Transcription is the first step of protein synthesis.
  It is broken into three major steps:
  Step 1: Initiation (RNA polymerase binds onto the promoter)
  Step 2: Elongation (RNA polymerase moves across the DNA strand and synthesises)
  Step 3: Termination (Ending of transcription, the mRNA strand is complete and it detaches from DNA)
• Transcription occurs in the nucleus only

Question 17

What happens during translation?

Answer 17

• mRNA to protein
  1. mRNA connects to a ribosome
  2. tRNA brings amino acids
  3. Amino acids join together
  4. Protein is finished and released.
• Translation occurs in the cytoplasm and at the ribosome.

Question 18

What is mRNA? What is its function?

Answer 18

• mRNA stands for messenger ribonucleic acid.
• mRNA carries the instructions for one gene
• mRNA is synthesised in the nucleus
• Its function is to make a copy of a gene and take it to a ribosome, where amino acids are assembled to make a protein

Question 19

What is rRNA? What is its function?

Answer 19

• rRNA stands for ribosomal RNA
• The rRNA is responsible for linking the amino acids in a pre-determined order to form proteins.

Question 20

What is tRNA? What is its function?

Answer 20

• tRNA stands for transfer RNA
• tRNA molecules ferry the amino acids to the mRNA at the ribosome
• tRNA links with the ribosome and matches its anticodon with the codon of the mRNA
• A peptide bond forms between the adjoining amino acids, forming a polypeptide. The tRNA is removed to be used again.

Question 21

What is the role of the ribosome?

Answer 21

To translate the genetic code transcribed in mRNA into an amino-acid sequence

Question 22

What is a codon?

Answer 22

Three nucleotides found on the mRNA that codes for a specific amino-acid.

Question 23

What is an anticodon?

Answer 23

Three nucleotide sequences found on the tRNA that bind with the mRNA sequence

Question 24

What is a triplet?

Answer 24

A sequence of three nucleotides that determines ONE amino acid

Question 25

What is a polypeptide chain?

Answer 25

A string of amino acids connected by peptide bonds. They are the building blocks for proteins or amino acids.

Question 26

How are polypeptide chains and proteins different?

Answer 26

A polypeptide is a chain of amino acids linked together by peptide bonds. Whereas the protein is made up of one or more polypeptide chains folded to a specific three-dimensional structure, in which determines its functions.

Question 27

What is tRNA? What is the role of tRNA?

Answer 27

- Is a small RNA molecule that helps decode mRNA sequences into proteins. - It brings specific amino acids to the ribosomes during translation, the process of assembling proteins based on instructions provided by the mRNA.

Question 28

What are mutations?

Answer 28

Changes in the DNA sequence of an organism

Question 29

When do mutations occur?

Answer 29

DNA mutations occur during cell division (mitosis) where abnormal cells are replicated

Question 30

What can mutation be?

Answer 30

1. Harmful (benign or malignant) 2. Beneficial (HIV resistance, lactose tolerance) 3. No effect on organism

Question 31

What causes them?

Answer 31

1. Can come about spontaneously due to errors in DNA replication 2. Induced by mutagens (environmental factors that cause changes in DNA) such as - X-rays/radiation - Chemicals, poisons - UV Light

Question 32

What is a point mutation?

Answer 32

A change in a single nucleotide base in a DNA sequence. This can be a substitution of one base for another (eg; A to G). This changes the codon in the mRNA and potentially the amino acid in the protein.

Question 33

What is addition/insertion mutation?

Answer 33

The addition of one or more nucleotide bases into the DNA sequence. Eg; if an extra cytosine is added, it shifts the reading frame and changes all downstream codons, resulting in a completely different/non-functioning protein.

Question 34

What is deletion mutation?

Answer 34

The loss of one or more nucleotide bases in the DNA sequence. They cause frameshift mutations if they are not in multiples of 3, altering the downstream amino acid sequence.

Question 35

How do mutations impact protein synthesis?

Answer 35

1. DNA affected (Substitution, Insertion, or deletion) 2. This results in the mRNA being copied incorrectly. (incorrect nucleotide sequences) 3. Codes for wrong amino acid(s). 4. Formation of incorrect protein

Question 36

What is Huntington’s Disease?

Answer 36

A progressive brain disorder that affects the central area of the brain as well as movement, mood, and thinking skills.

Question 37

What is Sickle cell anaemia?

Answer 37

An inherited blood disorder marked by defective haemoglobin.

Question 38

What happens in Sickle cell anaemia?

Answer 38

- Only one amino acid changes in the haemoglobin - The haemoglobin still function but folds differently, changing the shape of the red blood cell, and affecting the way it carries oxygen - Blocks blood, causes tissue damage and pain.