8.2- DNA AND CHROMOSOMES

Question 1

What are the two types of cells?

Answer 1

prokaryotic cells

eukaryotic cells

Question 2

What are the DNA molecules of prokaryotic cells i.e. bacteria like? (3)

Answer 2

shorter
form circle
not associated with protein molecules

Question 3

Do prokaryotic cells have chromosomes?

Answer 3

no

Question 4

What are the DNA molecules of eukaryotic cells like? (3)

Answer 4

longer 
form line (linear)
occur in association with proteins called histones to form structures called chromosomes

Question 5

What in eukaryotic cells also contain DNA? (2)

Answer 5

mitochondria

chloroplasts

Question 6

What is the DNA of the mitochondria + chloroplasts in eukaryotic cells like? (3)

Answer 6

short
circular
not associated with proteins

Question 7

When are chromosomes only visible as distinct structures?

Answer 7

when cell dividing

Question 8

How are the chromosomes for the time that the cell is not dividing?

Answer 8

widely dispersed throughout nucleus

Question 9

How do the chromosomes appear when they first become visible at the start of cell division?

Answer 9

chromosomes appear as two threads, joined at single point

Question 10

What is each thread called? (chromosomes appear as two threads, joined at single point)

Answer 10

chromatid

Question 11

Why is each thread called a chromatid?

Answer 11

as DNA has already replicated to give two identical DNA molecules

Question 12

What is the DNA in chromosomes held by?

Answer 12

histones

Question 13

What is done to the considerable length of DNA found in each cell?

Answer 13

highly coiled + folded

Question 14

What sort of helix is DNA?

Answer 14

double helix

Question 15

What is done the DNA helix to fix it in position?

Answer 15

helix wound around histones to fix it in position

Question 16

What happens to the DNA-histone complex?

Answer 16

it’s then coiled

Question 17

What happens after the DNA-histone complex is coiled?

Answer 17

looped + further coiled before being packed into chromosome

Question 18

What can happen as the DNA-histone complex is coiled + looped + further coiled before being packed into chromosome?

Answer 18

a lot of DNA is condensed into a single chromosome

Question 19

How many DNA molecules does does a chromosome contain?

Answer 19

a single molecule of DNA

Question 20

What does a single molecule of DNA have along its length?

Answer 20

many genes

Question 21

What does each gene occupy?

Answer 21

specific position (locus) along DNA molecule

Question 22

In most species, what sort of number of chromosomes are in the cell of adults?

Answer 22

even number of chromosomes

Question 23

What are sexually produced organisms the result of?

Answer 23

fusion of sperm + egg, each of which contributes one complete set of chromosomes to offspring

Question 24

What is one of each pair of chromosome derived from in sexually produced organisms?

Answer 24

one of each pair derived from chromosomes provided by mother in egg (maternal chromosome) + other derived from chromosomes provided by father in sperm (paternal chromosomes)

Question 25

What are the pair of chromosomes known as?

Answer 25

homologous pairs

Question 26

What is the total number of chromosomes referred to as?

Answer 26

diploid number

Question 27

What is the diploid number in humans?

Answer 27

46

Question 28

What is a homologous pair always?

Answer 28

always two chromosomes that carry same genes but not necessarily same alleles of genes

Question 29

What happens to chromosomes number in meiosis?

Answer 29

halving of number of chromosomes

Question 30

What is the way that meiosis done ensure?

Answer 30

each daughter cell receives one chromosomes from each homologous pair

Question 31

What does it mean as each daughter cell receives one chromosomes from each homologous pair from meiosis?

Answer 31

each cell receives one gene from each characteristic of organism

Question 32

What happens when the haploid cells combine?

Answer 32

diploid state, with paired homologous chromosomes restored

Question 33

What is an allele?

Answer 33

one of number of alternative forms of gene

Question 34

How many different forms does each gene exist in?

Answer 34

two, occasionally more

Question 35

What is the different forms a gene exists in called?

Answer 35

gene

Question 36

Where does each individual inherit one allele from?

Answer 36

each of its parents

Question 37

Can the alleles inherited from the parents be the same or different?

Answer 37

may be same or different

Question 38

What is each allele like if an individual inherits different alleles?

Answer 38

each allele has different base sequence , so different amino acid sequence, so produces different polypeptide

Question 39

What is a mutation?

Answer 39

change in base sequence of gene producing new allele of that gene

Question 40

What does a mutation result in (hint- amino acids)

Answer 40

different sequence of amino acids being coded for

Question 41

From a mutation, what will the different sequence of amino acids being coded for lead to?

Answer 41

production of different polypeptide + hence different protein

Question 42

What happens sometimes with the different protein produced from a mutation?

Answer 42

different protein may not function properly or may not function at all

Question 43

When the different protein produced from a mutation is an enzyme, what can happen?

Answer 43

may have different shape

Question 44

If the different protein produced from a mutation is an enzyme and it has a different shape, what may happen?

Answer 44

new shape may not fit enzyme's substrate

Question 45

What happens if the new shape may not fit enzyme's substrate due to mutation?

Answer 45

enzyme may not function + this can have serious consequences on organism