Nucleic Acids, Mitosis And ATP

Question 1

What are nucleic acids?

Answer 1

Biologicalmolecules that carry important information. They are molymers of many monomers called nucleotides

Question 2

Describe the roles of DNA and RNA

Answer 2

DNA stores genetkc information inside the cell
RNA transferes the genetic information from DNA to ribosomes

Question 3

What are the components of DNA nucleotides

Answer 3

4 bases (adenine, thymine, guanice, cytosine)
Deoxyribose sugar
Phosphate group

Question 4

Describe the structure of DNA polynucleotides

Answer 4

Poly nucleotides join during a dindensation reaction
each nucleotide is held by strong covalent bonds called phosphodiester bonds between the phosphate group of one and the sugar of another.
Creates a sugar-phosphate backbone

Question 5

Descrobe the structure of a DNA molecule

Answer 5

Two polynucleotides running anti-parallel to eachother
Twist to form a double helix
Complimentary base paring- hydrogen bonds between the complimentary bases of each strand

Question 6

Describe what complimentary base pairing is

Answer 6

Adenine and thymine join with 2 hydrogen bonds
Guanine and cytosine join with 3 hydrogen bonds

Question 7

What is the difference between pyramidines and purines, give examples of each

Answer 7

Puramidines are smaller bases (thymine and cytosine)
Purines are larger bases (guanine and adenine)

Question 8

Give the adaptations of the structure of DNA

Answer 8

Double helix with many hydrogen bonds- stable molecule
Sugar-phosphate backbone- strong
Complimentary base pairing- allows DNA to replicate via semi-conservative replication (as weak hydrogen bonds can break)
Long and compact- stores lots of info in a small space
Precise genetic coding- allows protein synthesis

Question 9

What is the only way that polynucleotides can differ from eachother?

Answer 9

Different sequences of bases in the polynucleotide

Question 10

Describe the structure of RNA and its components

Answer 10

RNA is a ribonucleic acid, it is short singke stranded polynucleotide made lf RNA nucleodide monomers
Each nucleotide contains a phosphate group, nitrogen containing bases (adenine, uracil, cytosine, guanine) and a ribose sugar

Question 11

What is semi-conservative replication?

Answer 11

DNA replication where half of the origional DNA molecule is conserved, and the other half is newly synthesised

Question 12

Describe the process lf semi-conservative replication

Answer 12

enzyme DNA helicase unwinds double helix by BREAKING the hydrogen bonds between bases. separates polynucleotide strand
Each exposed strand now acts as template
Single DNA nucleotides found free in nucleoplasm are attracted to exposed bases, and attach by complimentary base pairing with new hydrogen bonds
Enzymes DNA polymerase joins the new nucleotides together with phosphodiester bonds in comdensation reaction. This forms new polynucleotide,

Question 13

When and by which scientists was the experiment for evidence of semi-conservative replication?

Answer 13

1958
Stahl and Meselson

Question 14

Explain the evidence for semi-conservative replication

Answer 14

Cultures of E-coil bacteria grown in medium of 15N (heavy isotope)
All DNA becomes labelled with 15N
Transfered and grown in medium with 14N (lighter/ normal isotope)
Samples taken, each generation of DNA was extracted and centrifuged

Gen 0- DNA all heavy
Gen 1- two hybrid molecules of DNA
Gen 2- 50% light, 50% hybrid
Gen 3- 75% light, 25% hybrid

Question 15

What is a chromosome?

Answer 15

Long, linear structures consisting of DNA and histone proteins

Question 16

What are a homologous pair of chromosomes?

Answer 16

A pair pf chromosomes containing the same gene in the same position, each derived from a different parents gamete

Question 17

How many homologous pairs of chromosomes does a human cell contain?

Answer 17

23

Question 18

What is the diploid number of chromosomes? (Definition)

Answer 18

The total number of chromosomes in a normal cell

Question 19

What is the diploid number of chromosomes in a human cell?

Answer 19

46

Question 20

State and describe the 4 stages in the cell cycle

Answer 20

G1- cell prepares for replication (respires, grows, produces new organelles and proteins)
S- DNA replicates by semi-conservatove replication
G2- cell grows and prepares for mitosis
M- mitosis

Question 21

What three stages in the cell cycle can be described as interphase?

Answer 21

G1, S and G2

Question 22

What does it mean if a cell is in stage G0 of the cell cycle?

Answer 22

Some cells within multicellular organicms are soecialised to not divide, so are in G0

Question 23

How does the diration of interphase indicate the rate of cell division?

Answer 23

The shorter the interphase stage, the more rapid the rate of division

Question 24

Explain the stages of mitosis

Answer 24

Prophase- chromosomes shorten and become visible. Nuclear envelope breaks down
Metaphase- chromosomes line up along the equator of the cell and attach to spind fibres by their centromeres
Anaphase- centromere divides, spindle fibres contract to pull apart sister chromosomes to opposite okles of the cell
Telophase- chromosomes uncoil, become thread like again and not visible.new nuclear envelope forms around each set of daughter chromosomes.

Question 25

Explain the process of cytokinesis

Answer 25

After mitosis, the cell pinches itself in two and a cell membrane forms in the middle. The cell membrane from one side of the cell joins that of the opposite side, the cell splits and creates two daughter cells

Question 26

What is the mitotic index and what is its equation?

Answer 26

A ratio that shows the number of cells undergoing mitosis compared to the total number of cells = number of cells in mitosis/ total number of cells

Question 27

State and explain how prokaryotic cells divide

Answer 27

Binary fission: Replicate circular DNA and plasmids The cell memnrane grown between the two main circular DNAs and pinches inwards, dividing the cytoplasm in two A new cell wall forms, forming two daughter cells each with one main circular DNA and variable number of plasmids

Question 28

Why can prokaryotic cells not divide by mitosis?

Answer 28

They have no nucleus, therefore have no histone proteins so DNA cannot coil and chromosomes cannot be made)

Question 29

Explain how viruses divide

Answer 29

They attach to host cells using attachment proteins that are complimentary to the host cells antigens They inject their nucleic acids into the host cell, which uses the nucleic acids to produce viral compoments that can be assembled into new viruses

Question 30

What is cancer and how is it caused?

Answer 30

Results from mutations in genes that cause uncontrolled and rapid cell division of cells by mitosis Forms a mass of abnormal cells called a tumour Tumours dont respond to signals from nerves or hormones, so cannot undergo programmed cell death

Question 31

What are treatments lf cancer?

Answer 31

Drugs can be used so that parts of the cell (such as DNA replication or spindle fibre formation) can be blocked to control/ stop the rate of division

Question 32

What is ATP?

Answer 32

ATP is an immediate source of energy used by all cells to drive their metabolic reactions

Question 33

What are the components of an ATP nucleotide?

Answer 33

3 phosphate groups Organic base adenine Ribose sugar

Question 34

Explain how ATP is synthesised

Answer 34

By the addition of ADP to an inorganic phosphate (Pi) This is a condensation reaction that is catalysed by the enzyme ATP synthase, it occurs during respiration and requires an input of energy

Question 35

What is the reaction called when ATP is synthesised?

Answer 35

Phosphorylation

Question 36

Explain the breakdown of ATP

Answer 36

The phosphate- phosphate bond between the 2nd and 3rd phosphate is broken during a hydrolysis reaction, using the enzyme ATP hydrolase. This removes one inorganic phosphate group and releases energy. ATP becomes ADP

Question 37

Between which bonds is useful energy stored in ATP?

Answer 37

Between the phosphate- phosphate bond between the second and third ohosphates. This is because it is very unstable and easily broken

Question 38

What is the use of ATP, give examples of when it is used?

Answer 38

Energy is released during its hydrolysis, which can be used in metabollic reactions that require energy: Active transport Exocytosis Synthesis of substances Movement of muscle cells Activation of other molecules

Question 39

What are benefits of ATP as an intermediate energy source compared to glucose?

Answer 39

Hydrolysis of ATP is a single reaction, so energy is immediately available. Glucose hydrolysis uses more reactions ATP is soluble, so can easily move around cells without passing through cell membranes. Glucose is insoluble ATP releases small amounts of energy. Glucose releases large amounts of energy that are not needed, so is less efficient

Question 40

What is the ATP cycle?

Answer 40

The condensation of ATP from ADP and Pi and the hydrolysis of ATP is a reversable reaction, so described as a cycle

Question 41

why is ATP not s good long term energy source?

Answer 41

Due to the instability in the phosphate group bonds

Question 42

What are chromatids?

Answer 42

One of two threads of a chromosome, formed after DNA replication

Question 43

What is a centromere?

Answer 43

Holds together two identical sister chromosomes, in the centre of the chromosome

Question 44

What are chromatins?

Answer 44

a substance formed from DNA and proteins together

Question 45

Which two scientists proposed the DNA structure and replication?

Answer 45

Watson and Crick

Question 46

Give two uses for the hydrolysis of ATP

Answer 46

To release energy from chemical reactions To add phosphate groups to other molecules, to make them more reactive/ change their shape

Question 47

What are gametes?

Answer 47

The sex cells involved in sexual reproduction