DNA structure and replication

Question 1

what must genetic material have

Answer 1

1) contain complex information
2) replicate faithfully
3) encode the phenotype
4) have the capacity to vary

Question 2

what are the three components which make up a nucleotide

Answer 2

a five carbon sugar
a base
one or more phosphate groups

Question 3

outline DNA structure

Answer 3

• nucleotide subunits
• give carbon sugar and phosphate groups form the backbone
• phosphate groups have negative charge on its oxygen atoms

Question 4

what types of bonds link together nucleotides

Answer 4

phosphodiester bonds = linkage is very stable despite changes in PH temperature

Question 5

what bases make up the double ring structures known as purines

Answer 5

adenine and guanine

Question 6

what bases make up single ring structures known as pyrimidines

Answer 6

thymine and cytosine

Question 7

what are the differences between DNA and RNA

Answer 7

DNA - deoxyribose, Thymine, monophosphate, very large, double stranded

RNA - ribose, uracil, triphosphate, smaller, single stranded

Question 8

what is the difference between positive and negative supercoiling

Answer 8

positive- twisted in the same direction as the DNA double helix (overwound DNA)

negative - twisted in the opposite direction as the DNA (underwound DNA)

Question 9

how is DNA packed in prokaryotes

Answer 9

The DNA double helix in the circular bacterial chromosome is folded by DNA binding proteins into supercoil loops that protrude from a denser core

Question 10

How is DNA packed in eukaryotes

Answer 10

the DNA is wrapped around histones forming nucleosomes which are condensed into chromatin which is packed into chromosomes

Question 11

what is a nucleosome

Answer 11

a flattened sphere consisting of approximately 150 nucleotides wrapped twice around two molecules of each histone

Question 12

what is a histone

Answer 12

proteins rich in positively charged amino acids lysine and arginine which enable formation of ionic bonds with negatively charged sugar phosphate backbone of the dna

Question 13

what is semiconservative replication

Answer 13

when two DNA strands separate and are each used as a template for a new strand

Question 14

what is DNA polyermase

Answer 14

1) DNA plymerization occurs only in the 5-3 direction and is catalysed by DNA polyermase

2) its basic function is to synthesize a new DNA strand from an existing template
most also correct mistakes made in replication

Question 15

what are okazaki fragments

Answer 15

as parental strand is unwound a new piece is initiated at intervals and each new piece is elongated until it reaches the bit infront, these short pieces are okazaki fragments

Question 16

what are the 4 key enzymes involved in DNA replication

Answer 16

1) RNA primase- makes the primer to start a new strand
2) DNA polyermase- elongates the primer adding nucelotides
3) a different polyermase removes primer and replaces with nucleotides
4) DNA ligase- joins okazaki fragments

Question 17

how is DNA polyermase used in proofreading

Answer 17

it can detect the number of hydrogen bonds forming between base on the template and new base, if an error is detected the DNA polymerase removes it and inserts the correct one

Question 18

what are the different types of chromosome found in eukaryotes

Answer 18

1) sex chromosomes
2) autosomal chromosomes

Question 19

outline chromosome replication on the leading strand

Answer 19

1) only one primer is needed to start synthesise
2) replication continues to the end
3) strand is replaced by DNA when ast fragment of lagging strand catches up

Question 20

outline chromosome replication in the lagging strand

Answer 20

1) multiple RNA primers needed
2) final primer is added about 100 nucleotides from the 3 end
3) when removed a new daughter strand is shortened by about 100 nucleotides

Question 21

what is a telomeres

Answer 21

short repetitive areas of DNA at the end of chromosomes consisting of repeated TTAGGG sequences

Question 22

what are the five stages of mitosis

Answer 22

prophase
prometaphase
metaphase
anaphase
telophase

Question 23

outline prophase

Answer 23

chromsomes condense and centrosomes radiate microtubules and migrate to opposite poles

Question 24

outline prometaphase

Answer 24

microtubules of the mitotic spindle attach to chromosomes

Question 25

what are kinetochores

Answer 25

two protein complexes associated with centromeres and forms the site of attachment for a single microtubule

Question 26

outline metaphase

Answer 26

chromosomes align in the centre of the cell

Question 27

outline anaphase

Answer 27

sister chromatids separate and travel to opposite poles

Question 28

outline telophase

Answer 28

nuclear envelope reforms and chromosomes decondense

Question 29

what is cytokinesis

Answer 29

at the end of mitosis the parent cell divides into two daughter cells