DNA

Question 1

What is a DNA polymer and what does it consist of?

Answer 1

Nucleotide
Deoxyribose (pentose sugar)
A phosphate group
And a nitrogenous base

Question 2

What are the 4 nitrogenous bases?

Answer 2

Adenine
Thymine
Guanine
Cytosine

Question 3

Which bases are purine?

Which are pyrimidines?

Answer 3

Adenine and Guanine are Purines

Thymine and Cytosine are pyrimindines

Question 4

How many hydrogen bonds between Thymine and Adenine

“” Cytosine and Guanine

Answer 4

Two between a and t

Three between c and g

Question 5

How are nucleotides joined together?
What reaction?
What bond?

Answer 5

Bonding between phosphate group on one nucleotide and deoxyribose sugar on another
Condensation
Phospodiester

Question 6

What is a locus?

Answer 6

Each gene occupies a fixed position on a particular chromosome

Question 7

What is a gene?

Answer 7

A gene coded for a polypeptide. It determines the sequence of amino acids in the primary structure. An allele is a version of a gene

Question 8

What are the two stages of protein synthesis?

Answer 8

Transcription and translation

Question 9

Where does transcription take place?

Answer 9

Takes place in the nucleus and involves “copying out” the genetic code as messenger RNA which can leave the nucleus.

Question 10

Where does translation take place?

Answer 10

Takes place at ribosomes and involves changing a sequence of bases into a sequence of amino acids

Question 11

Describe the process of transcription

Answer 11

1. The RNA polymerase attaches to the start of the DNA (gene) to be expressed. The DNA unwinds and hydrogen bonds break
2. One strand acts as a template strand. RNA polymerase moves along the template strand and lines up free RNA nucleotides by complementary base pairing to the DNA template strand
3. RNA polymerase causes the RNA nucleotides to join together by a condensation reaction, forming a molecule of mRNA phosphodiester bond
4. The mRNA leaves the nucleus via a nuclear pore

Question 12

What is Mitosis?

Answer 12

Cell division which produces 2 genetically identical daughter cells

Question 13

Explain the significance of mitosis

Answer 13

Daughter cells are genetically identical because the DNA is copied exactly during interphase by semi-conservative replication
This is important as all new cells must have the full genome (all the genes)
Mitosis produces new cells for growth, repair, cell replacement and new organisms in asexual reproduction in yeast, plants and animals

Question 14

Draw a diagram showing the cell cycle

Or explain

Answer 14

New cell is formed
-undergoes G1 where new proteins and organelles are made
Interphase- G1, S, G2
S stage dna replicates
-G2 proteins needed for cell division made
Synthesis of ATP
- then mitosis

Question 15

What happens in propase?

Answer 15

Centrioles move apart
Nuclear membrane breaks down
DNA coils and condenses
Spindle fibres form

Question 16

What happens during metaphase?

Answer 16

Chromosomes aligned on the equator

Nuclear envelope broken down

Question 17

What happens during anaphase?

Answer 17

Centromeres divide and sister chromatids are pulled apart to opposite poles of the cell by the spindle fibres

Question 18

Wha happens in telophase?

Answer 18

Chromotids reach opposite poles of the cell and chromotids unwind
Nuclear membranes reform around the two nuclei.
Cytoplasm divides into 2 cells

Question 19

What happens in cytokinesis?

Answer 19

Cell splits

Question 20

What happens during meiosis -prophase 1?

Answer 20

Each duplicated, condensed chromosomes pairs with its homologue
Homologise swap segments
Each chromosome becomes attached to microtubules of newly forming spindle

Question 21

What is crossing over?

Answer 21

Each chromosome becomes zippered to its homologue
All four chromotids are closely aligned
Maternal and paternal chromatids exchange segments

Question 22

What factors cause variation among offspring

Answer 22

Crossing over during prophase I

Random alignment of chromosomes at metaphase 1

Random combination of gametes at fertilisation