Topic 6a DNA & Reproduction

Question 1

What are chromosomes made up of

Answer 1

Long molecules of coiled up DNA

Question 2

Why are DNA molecules described as double helix

Answer 2

Because they are made up of two strands coiled up together in the shape of a double helix

Question 3

How does a gene help to make a specific protein

Answer 3

It tells the cells in what order to put together the amino acids in order to make a specific protein.

Question 4

Define the word Genome

Answer 4

A Genome is the entire set of genetic material in an organism

Question 5

Why is understanding the human Genome important for science and medicine

Answer 5

• It allows scientists to identify genes in the Genomes that are linked to specific diseases

Question 6

What is a nucleotide made of

Answer 6

One sugar molecule, One Phosphate molecule (Sugar and Phosphate Backbone) and one base pair AT, CG,

Question 7

Which part of the nucleotide alternate to from a DNA Strand

Answer 7

Sugar and Phosphate molecules alternate e.g. sugar, phosphate, sugar, phosphate

Question 8

How many bases code for an amino acid

Answer 8

3 bases e.g. Asparagine = AAT

Question 9

How does the sequence of bases in a gene control which particular protein is made

Answer 9

Each sequence of three bases is coded to a specific amino acid. These amino acids are joined together to form a particular protein depending on the order of the bases e.g. TCT codes for Serine

Bases code for amino - amino form particular protein

Question 10

In what order are the components of a nucleotide joined together

Answer 10

Base is always attached to the sugar and the the sugar attaches to the a phosphate

Question 11

Where are proteins assembled

Answer 11

Proteins are made in the cell cytoplasm on tiny structures called ribosomes

Question 12

What is the role of mRNA

Answer 12

mRNA is a copy of the DNA code for protein taken from the nucleus and moved to the ribosomes where protein is then synthesised

MRNA - copy of DNA code for protien - moved form nucleus - to ribosomes (for synthesis)

Question 13

How many different amino acids are there in humans

Answer 13

20

Question 14

What are carrier molecules and what do they do

Answer 14

They bring amino acids to the ribosomes in the correct order in order to assemble and form a unique shape (A Protein to perform a specific task) i.e Enzymes, Hormones, Structural Proteins

Question 15

What happens when a protein chain is complete

Answer 15

It forms a unique shape to perform a specific task

• Enzymes = Biological catalyst to speed up chemical reactions
• Structural Protein = a physically strong structure like collagen which strengthens connective tissue
• Hormones = Used to carry messages around the body e.g. insulin to regulate blood glucose levels

Form unique shape - for specific function - enzyme/hormone/ structural protein

Question 16

What is a mutation in genes and how does is occur

Answer 16

A mutation is a random change in an organisms DNA

It occurs when a gene isn’t quite replicated properly changing the sequence of DNA bases in a gene

Question 17

How do mutations affect proteins

Answer 17

Mutations can sometimes lead to changes in proteins as mutations change the sequence of DNA Bases in a gene. These bases code for the sequence of amino acids that make up proteins. Mutations can alter the proteins shape affecting enzyme substrates ability to bind to its active site as the shape of the site has changed.

Mutation changes base sequence in gene leading to changes in protein - alter shape of protein - substrate cant fit active site

Question 18

True or false Mutations occur continuously

Answer 18

True

Question 19

What are insertions in regards to Mutation

Answer 19

Change in base sequence - which changes the amino acid the 3 bases code for
An insertion refers to a change in the DNA base sequence where it shouldn’t be. It changes the way the groups of the three base pairs are read which in turn changes the amino acid they code for.

(EXTRA LETTER INSERTED) e.g -
Origional gene = TAT/AGT/CTT

Insertion = TAT/AGG/TCT/T insertion has caused for a different amino acid to be coded for

Question 20

What are Deletions in regards to mutations

Answer 20

Deletions are when a random base is deleted from the DNA Base sequence. Like insertions they alter the way that the base sequence is read and have a knock on effect further down the sequence.

Question 21

What are substitutions in regards to mutations

Answer 21

Substitutions are when a random base in the DNA base sequence is changed to a different base

Question 22

What is the difference between Sexual Reproduction and Asexual reproduction

Answer 22

Sexual Reproduction = Genetic information from 2 organisms is combined to produce offspring which are genetically different to either parent

ASexual Reproduction = Only one parent so offspring are genetically identical to the parent. No fusion of gametes, no mixing of chromosomes.

Question 23

What are Gametes

Answer 23

Gametes are reproductive/sex cells which unite during sexual reproduction.

Question 24

What is fertilisation

Answer 24

Fertilisation is the fusion of Gametes. In humans Male sperm fuses with female egg to form a cell with the full number of chromosomes half from the father and half from the mother.

Fusion of Gametes - form a cell - full no of chromosomes - Half Male Half Female

Question 25

Are Gametes produced by Meiosis or Mitosis

Answer 25

Meiosis = two divisions

Question 26

How are Gametes produced

Answer 26

Gametes are produced by meiosis. They only have 1 copy of each chromosome so that when gamete fusion takes place the right amount of chromosomes are present (two copies from each gamete)

To make gametes with only have half the amount of the original number of chromosomes the meiosis process involves two cell divisions.

Question 27

How many sets of chromosomes do gametes have

Answer 27

one

Question 28

Where are gametes produced

Answer 28

Reproductive organs

Question 29

How many new cells are produced when a cell divides by meiosis

Answer 29

4

Question 30

Following fertilisation, how does the resulting cell grow

Answer 30

By repeatedly dividing by Mitosis

Question 31

Advantages of Sexual reprodution

Answer 31

• Offspring have genetic information from both parents so there is a mixture of genetic information.
• This produces variety which increase the chance of a species surviving a change in environment.
• the species can adapt to new environments due to variation, which gives them a survival advantage.
• a disease is less likely to affect all the individuals in a population.

Question 32

Disadvantages to Sexual Reproduction

Answer 32

The disadvantages of sexual reproduction:

• time and energy are needed to find a mate
• it is not possible for an isolated individual to reproduce

Question 33

Advantages to Asexual reproduction

Answer 33

• the population can increase rapidly when the conditions are favourable
• only one parent is needed
• it is more time and energy efficient as you don’t need a mate
• it is faster than sexual reproduction

Question 34

Disadvantages to Asexual reproduction

Answer 34

• it does not lead to genetic variation in a population
• the species may only be suited to one habitat
• disease may affect all the individuals in a population

Question 35

When does the Malaria parasite reproduce Asexually

Answer 35

It produces Asexually when its in the human host

Question 36

Explain how a strawberry plant reproduces Asexually

Answer 36

It produces runners, these are stems that grow horizontally on the surface of the soil away from the plant. At various points along the runner a new strawberry plant will form which is identical to the original plant.