Mr P bio 9 The cell cycle

Question 1

What is a chromosome?

Answer 1

Very long condensed DNA molecule associated with proteins and contain many genes

Question 2

What protein is present in chromosomes?

Answer 2

Largely positively charges globular proteins called histones

Question 3

What is his histones role?

Answer 3

To organise and condense the DNA tightly so that it fits into the nucleus

Question 4

What is the structure of a chromosome?

Answer 4

Dependent on the stage in the cell cycle, a chromosome may have 1 chromatid or be made of 2 identical sister chromatids joined together at the centromere

Question 5

What are haploid cells?

Answer 5

Cells that have one copy of each chromosome

Question 6

What is a diploid cell?

Answer 6

Cells have 2 copies of each chromosome so one from each parent (in most organisms)

Question 7

In diploid cells what are the copies of the same chromosome called?

Answer 7

Homologous chromosomes

Question 8

What are homologous chromosomes?

Answer 8

They have the same genes but may have different alleles of the gene. (E.g. a pair of homologous chromosomes may carry the eye colour gene, one may carry blue eyes allele and the other brown eyes allele

Question 9

Which theory did Watson and Crick come up with for DNA replication?

Answer 9

Semi-conservative replication

Question 10

What are the steps of the semi-conservative theory?

Answer 10

1. DNA helicase attaches to DNA breaking H bonds between bases
2. Two strands start to separate
3. In nucleus, there are free nucleotides which contain 3 phosphate groups and are known as nucleotide triphosphates
4. Individual DNA nucleotides base pair with the exposed bases on seperating DNA
5. DNA polymerase connects new nucleotides together by catalysing condensation reactions between the sugar and phosphate groups of adjacent nucleotides within new strand
6. Polymerase breaks the 2 extra phosphates on the nucleotides + uses energy released to create the phosphodiester bonds
7. Occurs on both original strands so 2 copies are made and each new strand of DNA contians an original and a new strand and is genetically identical to the original DNA

Question 11

What are the steps of the Meselson Stahl experiment involving creating bacteria containing 15N?

Answer 11

1) bacteria grown in broth containing heavy (15N) nitrogen isotope
2) as bacteria replicates, uses nitrogen from the broth to make DNA nucleotides and after some time culture of bacteria had DNA only containing heavy (15N) nitrogen
3)sample of DNA from 15N culture of bacteria extracted and spun in a centrifuge showing that DNA containing heavy N settled near the bottom of the centrifuge tube

Question 12

What are the steps after the formation of 15N?

Answer 12

1)taken out of broth and added to a broth containing lighter 14N nitrogen which was left for enough time for 1 round of DNA replication to occur before DNA was extracted and spun in a centrifuge
2)if conservative DNA replication has occurred the original template DNA molecules would only contain heavy N and would settle at bottom of tube whilst new DNA molecules would only contain the light N and would settle at the top but the results showed semi- conservative replication had occurred all the DNA molecules would now contain heavy 15N and light 14N and would therefore settle in the middle of the tube

Question 13

What are the 3 phases of the cell cycle?

Answer 13

1. Interphase
2. Nuclear division (mitosis)
3. Cell division

Question 14

What are the stages within interphase?

Answer 14

G1 phase- cell increases in size and new biomass is made
S phase- DNA replicates
G2 phase-cell gets ready for division it makes stores of ATP and new organelles

Question 15

What is cytokinesis?

Answer 15

Period when the cell divides into 2 each daughter cell receiving one of the nuclei. Created 2 genetically identical cells.

Question 16

What occurs during mitosis?

Answer 16

In this form of nuclear division, the DNA molecules are copied, copies separated and passed to the 2 daughter cells. The daughter cells will be genetically identical to each other and to the original parent cell

Question 17

Why is mitosis important?

Answer 17

1. Growth of multicellular organisms
2. Replacement of cells and repair of tissues
3. Asexual reproduction

Question 18

What are the 4 processes of mitosis?

Answer 18

Prophase, metaphase, anaphase, telophase

Question 19

what is the process of prophase?

Answer 19

1)nuclear membrane stars to break down
2)centrioles start to move to the poles of the cell and make spindle fibres
3)the chromosomes condense and become visible. each chromosome is made up of 2 chromatids joined at the centromere

Question 20

what is the process of metaphase?

Answer 20

1)the centrioles complete the production of spindle fibres
2) the homologous pairs of chromosomes are attached to the spindle fibres and are aligned down the middle of the spindle. They attach via their centromeres

Question 21

what is the process of anaphase?

Answer 21

1) the spindle fibres contract and pull back to the poles
2)as they contract, they pull on the centromere, which splits
3) the sister chromatids are pulled to the opposite poles

Question 22

what is the process of telophase

Answer 22

1) the nuclear membrane starts to re-form around each set of chromosomes
2) the chromosomes unwind and become invisible
3)the sister chromatids are pulled to opposite poles

Question 23

what are oncogenes?

Answer 23

code for proteins that stimulate division (if mutated, the proteins may over stimulate cell division)

Question 24

what are tumour suppressor genes?

Answer 24

code for proteins that stop cell division (if mutated, the proteins may no longer inhibit cell division)

Question 25

what happens if a mutation occurs in one the control genes?

Answer 25

cell division may continue uncontrollably and rapidly and the cells produced are abnormal. a tumour develops.

Question 26

what is a benign tumour?

Answer 26

do not spread from their original site and do not cause cancer

Question 27

what is a malignant tumour?

Answer 27

tumours that spread through the body, invading and destroying other tissues and cause cancer

Question 28

how do malignant tumours interfere with the normal functioning of an organ?

Answer 28

they interfere with the organ/tissue on which they have stated to grow. they can break off the tumour and travel through the blood or lymphatic system to form secondary growths in other parts of the body

Question 29

what is the spreading of cancer via the blood or lymphatic system known as?

Answer 29

metastasis

Question 30

one method of treating cancer is through drugs, how do they work to prevent cell division?

Answer 30

the drugs may stop:
DNA synthesis
spindle formation
cytokinesis
or other processes linked to mitosis

Question 31

how do prokaryotes such as bacteria divide?

Answer 31

binary fission

Question 32

how is binary fission different from mitosis?

Answer 32

there is no nuclear envelope to breakdown and there are no spindle fibres present

Question 33

what is the process of binary fission?

Answer 33

1.the single, circular DNA molecule undergoes DNA replication
2.any plasmids present undergo DNA replication
3.the parent cell divides into two cells, with the cytoplasm roughly halved between the 2 daughter cells
4.the 2 daughter cells each contain a single copy of the circular DNA molecule and a variable no. of plasmids

Question 34

what do viruses structurally contain?

Answer 34

-a nucleic acid core
-a protein coat: capsid
-some viruses have outer layer called an ‘envelope’

Question 35

how do viruses replicate?

Answer 35

1. a virus uses attachment proteins on its surface to bind to complementary receptor proteins on the surface of a host cell
   2.inject their nucleic acid is inside a host cell, the hosts DNA replicating and protein synthesising systems make more virus particles
2. these are released when cell bursts or by ‘budding’ one t a time through the host cell membrane (exocytosis)

Question 36

what is a carcinogen?

Answer 36

A chemical, a form of radiation or other agent that causes cancer