Genes

Question 1

Definition of genes

Answer 1

• is a base sequence of DNA
  M1 that codes for amino acids sequences of a polypeptide
  M2 and a functional RNA

Question 2

Where do genes locate ?

Answer 2

In Locus

Question 3

What is a triplet code ?

Answer 3

• when 3 bases code for each amino acids

Question 4

Name of non coding and coding DNA

Answer 4

• introns 99%
• exons 1%

Question 5

E.g. why does the number of amino acids coded for coil be fewer than the number we see ? (2)

Answer 5

M1 99% of DNA are non coding introns
M2 they could be start/ stop codes

Question 6

Features of genetic codes (3)

Answer 6

M1 known as degenerate code because most amino acids are coded for by more than one triplets
M2 it is non- overlapping = only read once
M3 it is universal = each triplets codes for the same amino acids in all organisms

Question 7

Definition of gene

Answer 7

Is a sequence of DNA bases codes for a polypeptide or a functional RNA

Question 8

Definition in genome

Answer 8

• is a complete set of genes in cell

Question 9

Proteome

Answer 9

• is a full range of proteins that a cell is able to produce

Question 10

Functions of mRNA

Answer 10

• is a copy of a gene from DNA = instructed cells to make specific proteins
• leaves the nucleus to carry a copy of genetic code of a gene
• act as a template for translation

Question 11

Structure of mRNA

Answer 11

• single helix
• intermediate sizes
• chemically unstable, easily broken down
• bases of AUGC
• consist of codons that determines amino acids sequence of polypeptide they will make

Question 12

Functions of tRNA

Answer 12

• point of attachment attach with amino acids, transfer to ribosomes and attach to mRNA ‘s codons by anticodons to create polypeptide chain of amino acids

Question 13

Structure of tRNA

Answer 13

• bases AUGC
• clover leaf shaped
• single stranded
• smallest size
• intermediate stability
• consist of anticodons that binds to codons during translation

Question 14

Transcription process in eukaryotic cells (5)

Answer 14

M1) hydrogen bonds between DNA bases break
2) only one DNA strand acts as a template
3) free DNA nucleotides align by complementary base pairing
4) uracil in RNA pair with adenine in DNA
5) RNA polymerase joins adjacent nucleotides, form phosphodiester bond
6) pre- mRNA is spliced to remove introns to form mRNA

Question 15

Translation process (6)

Answer 15

1) mRNA attaches to ribosomes
2) anticodons of tRNA bind to complementary mRNA codons
3) tRNA brings a specific amino acid
4) amino acids join by peptide bond
5) amino acids join together with the use of ATP
6) tRNA released
7) ribosomes moves along the mRNA to form polypeptide

Question 16

What is gene mutation

Answer 16

A change in DNA base sequence of chromosomes

Question 17

How do induced mutations happen

Answer 17

• induced by mutagenic agents= increase RATE of mutation

Question 18

Example of mutagenic agents

Answer 18

• exposure to radiation = UV
• viruses
• microorganisms
• alcohol, smoking, diet

Question 19

What is chromosomes mutation

Answer 19

• a change in number or structure of chromosomes caused by errors in cell division

Question 20

Define substitution

Answer 20

-when one base in the DNA triplets is replaced by another base , changes nucleotides
- may not cause a massive change if the same amnio acid is produced because more than one triplet code for the same amino acid due to degenerate nature of genetic code

Question 21

Define deletion

Answer 21

• when a base of a DNA triplet is removed= causes all other triplets are read differently, each swift to the left by one base = frame shift

Question 22

Process of meiosis (6)

Answer 22

M1) DNA replicates in late interphase
2) crossing over occurs with chromatids swap over in homologous pairs
3) chromosomes line up by independent segregation with random separation in homologous pairs
4) two division take place
5) in 1st division, separation of homologous chromosomes and separation of sister chromatids in DNA division
6) finally produce 4 haploid cells

Question 23

How does meiosis increases genetic variability ?

Answer 23

• independent segregation
• crossing over of chromosomes

Question 24

Why is meiosis necessary ?

Answer 24

• to maintain the chromosomes number of a species
• os gametes are haploid while all other body cells are diploid

Question 25

Compare mitosis vs meiosis (4)

Answer 25

1) 1 cell division vs 2 division 2) involve body cells vs gametes 3) produce genetically identical cells vs genetically different cells 4) produce 2 vs 4 daughter cells

Question 26

Define chromosomes non disjunction

Answer 26

- failure of homologous chromosomes or sister chromatids to separate properly during cell division

Question 27

Define genetic diversity

Answer 27

- the total number of different alleles in a population - greater no. Of different alleles in a species = more genetic diversity = more species able to adopt to environmental changes

Question 28

Effect of low genetic diversity

Answer 28

- lower probability that species can withstand environmental changes = more likely to go extinct

Question 29

Define population

Answer 29

- group of individuals of the same species that live in same place and can inter- breed - differences between reproductive success of individuals affects alleles frequency in population

Question 30

Explain how natural selection produce changes within a species (4)

Answer 30

M1 variations cause by random mutation of alleles within the gene pool M2 some have advantages alleles and an adaptation that favour survival M3 more likely to survive and reproduce offspring which passes down their alleles M4 produce changes into frequency of alleles

Question 31

Reasons of selective breeding (3)

Answer 31

- increase yield / quality/ appearance of meat, fruit and veg etc - longer shelf life of food - pest resistant / resistance to disease = survive longer

Question 32

Explain why percentage of bases from the middle part of chromosomes and the end part are different ? (2)

Answer 32

M1 they have different base sequences M2 pre mRNA codes for different amino acids to different proteins made

Question 33

What is crossing over and independent segregation in meiosis ?

Answer 33

-part of chromatids in homologous pairs is exchanged causing different combination of alleles in same genes - random separation of homologous chromosomes

Question 34

Define polyploidy

Answer 34

When cells have more than two compete sets of chromosomes

Question 35

E.g. explain how a gene codes for a protein (2)

Answer 35

1) base sequence of DNA determines triplets code 2) triplet code for specific amino acids 3) amino acids sequence determines what specific protein made

Question 36

Define homologous chromosomes (2)

Answer 36

1) pairs of chromosomes 2) that are same in size and genetic alleles at the same loci

Question 37

E.g. describe and explain the appearance of one of the chromosomes before 1st division on meiosis (3)

Answer 37

1) chromosomes form by DNA replication 2) form 2 chromatids 3) sister chromatids holds by centromere

Question 38

What increase genetic variation other than main two ones in meiosis ? (2)

Answer 38

1) Random fusion of gametes 2) Produce new alleles combinations

Question 39

Describe how the production of messenger RNA (mRNA) in a eukaryote cell is different from the production of mRNA in a prokaryote cell. (2)

Answer 39

1) introns is not included in prokaryotes cells, only in eukaryotic 2) pre mRNA only made in eukaryotic, but not prokaryotes

Question 40

Explain the importance of meiosis in life cycle of organisms to reproduce sexually (3)

Answer 40

1) meiosis halves the number of chromosomes from diploid to haploid 2) this keeps chromosomes number correct when gametes fuse from one generation to next 3) introduces more genetic variation

Question 41

Explain how crossing over can contribute to genetic variation (3)

Answer 41

1) sections of chromatids exchanged 2) each sections have different alleles coded for 3) creates new combination of alleles

Question 42

Describe the role of tRNA in the process of translation (3)

Answer 42

1) anticodon is complementary to codon on mRNA 2) it carries a specific amino acid to mRNA 3) causes a correct sequence of amino acid to be made along polypeptide