Chapter 5; Mitosis And Stem Cells, Cancer

Question 1

What is a histone protein

Answer 1

-Globular protein, positively charged that is associated with dna
-role is to organize and condense dna to fit inside the nucleus

Question 2

What is a nucleosome

Answer 2

2 loops of dna, wrapped around 8 histoen proteins twice

Question 3

What is chromatin (2 definitions)

Answer 3

A chain of nucleosomes,
Or a tightly coiled combination of dna and histone proteins

Question 4

Which forms is dna found in during cell division and which form is it found in usually

Answer 4

Cell division, as chromosomes, bc condensed
Usually, as chromatin

Question 5

What is an allele

Answer 5

Different forms of the same gene

Question 6

What is a gene

Answer 6

Sequence of dna that codes for a protein.
Or specific sequence of nucleotide bases that codes for a specific sequence of amino acids, which codes for production of a specific polypetide

Question 7

What is a gene locus

Answer 7

Position where a gene is found in a chromosome

Question 8

Difference between homologous chromosomes and sister chromatids.

Answer 8

Homologous chromosomes, have similar centromère positon, similar shaped and size, and same gene loci, but may contain allele, so diff forms of the same gene

Sister chromatids are genetically identical strands of dna, so each strand of a sister chromatid consist of a molecule of dna therfore

Question 9

In which stage is a chromosome converted into a sister chromatid in the cell cycle

Answer 9

During s phase, of interohase when dna is replicated

Question 10

Explain the role of telomeres

Answer 10

Ensure that the ends of the dna molecule are replicated
(Bc copying enzyme is unable to move to the end of the dna molecule.)
To Prevent the loss of coding dna during cell division
So that normal cell division can still occur

Question 11

Explain what telomeres are

Answer 11

They act as buffer regions of non coding non essential dna
Which consist of short base sequences that are repeated rather than genes.
(So one strand is rich in guanine and one is rich in cytosine, but still contain all the base sequences)

Question 12

What is telomerase

Answer 12

Enzyme that adds bases to telomeres, so extends telomeres
so ensures that the very end as of the dna molecule are replicated

Question 13

Which cells do not have telomerase and what does this mean

Answer 13

Specialized cells eg heart cells do not
-so telomerase can therfore not top up telomeres
So bc copying enzyme can not run till end of dna molecule, the very ends are not replicated
So coding dna is lost with every cell division
And so normal cell division can not occur, bc vital dna is lost and cell dies

Question 14

Do prokaryotes have telomerase or not and explain

Answer 14

They do not because they have circular dna and not chromosomes

Question 15

Which cells do have telomerase

Answer 15

-embryonic stem cells
-b lymphocytes, to divide and produce plasma cells which can in turn produce antibodies

Question 16

What is the role of mitosis and give four reasons why it is important

Answer 16

To produce genetically identical daughter cells.

-to maintain chromosome number
-to repair damaged tissue and replace dead cells
-asexual reproduction
-growth of multicellular organisms

Question 17

State what happens in g1 phase of interphase

Answer 17

-protein synthesis, transcription and translation
-organelles are replicated
-size of cell increases

Question 18

State what happens in s phase of interphase

Answer 18

DNA replication, semi conservative,
So chromosomes are duplicated to form sister chromatids

Question 19

State what happens in g2 phase of interphase

Answer 19

-dna that is synthesized is checked for any errors
-preparations for cell division are made, eg tubulin protein is produced to make microtubules for mitosis spindle fibresz
-size of cell increases

Question 20

In which phase of the cell cycle is the cell committed to dividing by mitosis

Answer 20

S phase, interphase

Question 21

What are cell checkpoints

Answer 21

Occur between each phase of the cell cycle to ensure that
-cells have produced enough organelles
-have no damaged dna
-have grown large enough

Question 22

Give three reasons why the cell cycle should be controlled

Answer 22

-to prevent the formation of tumors, which occur from cells diving uncontrollably and rapidly
-so that some parts of a mammal can grow faster than other parts, eg in an injury increased cell division can increase healing
-rapid division of lymphocytes to increase immune function

Question 23

Explain prophase part of the cell cycle.

Answer 23

Chromatin condenses to form chromosomes, visible as sister chromatids.
-spindle fibres form, which are protein microtubules that emerge form centrosomes
-nucleolus breaks down and nuclear envelope also breaks down

Question 24

Explain metaphase part of the cell cycle

Answer 24

Centrosomeas reach opposite poles and spindle fibres continue to extend,

Chromosomes align at the equator, the metaphase plate

Spindle fibres attach to centromeres or kinetic ores which are protiens on the centrosome

Question 25

Explain anaphase part of the cell cycle

Answer 25

Spindle fibers separated at the centomere, bc it splits in two
Spindle fibres shorten
Separated sister chromatids pulled to opposite poles

Question 26

Explain what happens in telophase part of cell cycle

Answer 26

-chromosomes decondense and become long and thin again
Spindle fibres break down
Nuclear envelope forms around ecah set of chromomes and nucleolus reforms

Question 27

Explain what happens in cytokinesis

Answer 27

In plant cells, a cell plate is formed at the equator and so cytoplasm splits into two
In animal cells, a cleavage furrow is formed, so cell membrane divides into two

Question 28

Explain what a stem cell is

Answer 28

Cell that can divide by mitosis an unlimited number of times

Question 29

After a stem cell has divided, what are the two possible things that can happen to it

Answer 29

-can either remain a stem cell and can be used in (tissue repair, cell replacement and growth)
-can produce daughter cells that differentiate into specialized cells
(Not stem cells that differentiate only the daughter cells)

Question 30

3 roles of stem cells

Answer 30

-tissue repair
-cell replacement
-growth

Question 31

What is totipotency

Answer 31

Can differentiate into any cell type found from cells in the EMBRYO, or in the PLACENTA

Question 32

What is pluripotent

Answer 32

Can differentiate into any cell type from cells found in the embryo BUT NOT FROM IN THE PLACENTA

Question 33

What is multipotent

Answer 33

can only differentiate into specific cell types found throughout the body,
-eg bone marrow cells only differentiate into blood cells, like monocytes neutrophils

Question 34

Explain 4 factors of a cancerous cell cycle

Answer 34

-very short interphase (sod a replication is very error prone)
-cell checkpoints are not controlled
-no cell death
-rapid and ucntrollable mitosis

Question 35

Give two reasons why most mutations do not lead to cancer

Answer 35

-early cell death
-destroyed by Body’s immune system

Question 36

Explain what a mutagen is and give two examples

Answer 36

Substance that causes a mutation.
Eg,
-ionizing radiation (X-ray and gamma rays)
-virus infection (HIV)

Question 37

Explain how a tumor is formed

Answer 37

-Carcinogens cause mutations in genes controlling cell division, so an oncogene is switched on (cancer causing gene)
-mutations are not destroyed by early cell death or by being destroyed by immune system
-cell with mutation does not respond to cell checkpoints, and there is uncontrollable and rapid mitosis, and it grows into a mass of unspecialized cells (a tumor)
-tumor grows and is supplied with blood and lymph
-becomes a malignant tumor, so spreads throughout the body.
-Can cause secondary tumors aswell, where tumor breaks off from original one and spreads through lymph or blood (metastasis)

Question 38

What is a tumour

Answer 38

Mass of unspecialozed cells, that ouccurs form rapid and uncontrollable mitosis

Question 39

Difference between malignant and benign tumours

Answer 39

Malignant- cause cancer,
can spread throughout the body,
More likely to interfere with functions of organs
Benign- do not cause cancer,
Do not spread form site of origin
Less likely to interfere with functioning or organs

Question 40

Give two examples of benign cancers

Answer 40

-warts
-brain tumors

Question 41

What is metastasis

Answer 41

The movement of malignant cancers to other tissues (break off from original one and spread throughout lymph and blood)