Cell Reproduction (Chapter 10)

Question 1

Cell cycle

Answer 1

All the stages a cell goes through in its life

Question 2

5 stages in cell cycle

Answer 2

G0 - undergoing normal functions but not dividing
G1 - Growth 1 phase: growing larger, synthesising extra proteins for cell division, still performing normal functions
S - Synthesis phase; DNA molecules are duplicating
G2 - Second growth phase; final preparation and growth before mitosis
M - Mitosis; cell division

Question 3

The 3 checkpoints in the cell cycle

Answer 3

1. Cell growth checkpoint - occurs towards the end of the growth phase (G1). Checks whether the cell is big enough and has made proper proteins for the synthesis phase.
2. DNA synthesis checkpoint - Occurs during synthesis phase (S). Checks whether DNA has been replicated correctly.
3. Mitosis Checkpoint - Occurs during the mitosis phase (M). Checks when mitosis is complete

Question 4

Mitosis

Answer 4

Mitosis is a process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei. There is 4 phases:
Prophase
Metaphase
Anaphase
Telophase

A continuous process that is important because it creates new body cells that are needed for growth, repair and maintenance

Question 5

What occurs in prophase?

Answer 5

-Centrioles become visible, and move to poles of cell
-spindle fibres form from the centrioles
-DNA goes from chromatin to chromosomes

By the end of this stage, the nucleus has disappeared and the chromosomes are making their way to the middle to line up along the cells equator

Question 6

What occurs in metaphase?

Answer 6

Chromosomes, attached to spindle fibres, are aligned in the middle of the cell.

Question 7

What occurs in anaphase?

Answer 7

Chromosomes are pulled back by the spindle fibres, splitting into individual chromatids (now called chromosomes again).

Pulled back towards the poles and centrioles.

Question 8

What occurs in telophase?

Answer 8

Two new nuclei reform around the chromosomes at each pole.
Spindle fibres and centrioles reabsorbed.
Chromosomes relax back into chromatin.
Cytoplasm may start to pinch inwards.

Question 9

What occurs in cytokinesis?

Answer 9

Cyto = cell and kinesis = split

Protein molecules for a contractile ring that contract the cell in the middle to form a figure 8 shape that gradually deepens until the cell splits into two.

Question 10

How does cell differentiation occur?

Answer 10

through methylation and acetylation, in which some genes are turned on and others are turned off

Question 11

How many chromosomes do human somatic cells have versus gametes?

Answer 11

• All human somatic cells have 46 chromosomes - this is referred to as the diploid chromosome number (2n)
• The gametes, or sex cells however have 23 chromosomes - this is referred to as the haplod chromosome number (n)

Question 12

What is meiosis, and where does it occur?

Answer 12

• Meiosis is a special process of nuclear division which results in the production of sperm or ova
• Meiosis involves two divisions and results in fourdaughter cells
• Each daughter cell contains only half the original number of chromosomes, the haploid number (23 or n).
• It takes place in the sex organs – the testes for
  sperm and the ovaries for ovum.

Question 13

Prophase I

Answer 13

Interphase at the start, DNA is replicated. Doesnt occur before prophase II

• Already replicated chromatin threads condense to form (‘X’ shaped) chromosomes (pairs of chromatids joined by centromere)
• Chromosomes gradually move to equator and find their homologous pair
• Nucleolus and nuclear membrane disappear
• Spindle forms

Question 14

Metaphase I

Answer 14

• Chromosomes line up at equator, attached to spindle fibres by their centromeres.
• However, this time each chromosome is
  lined up side by side with it’s homologous pair

Question 15

Anaphase I

Answer 15

Spindle fibres contract pulling homologous chromosomes to opposite poles.

Each pole contains one complete set of chromosomes

Question 16

Telophase I

Answer 16

• Chromosomes uncoil into chromatin, nuclear
  membrane forms, spindle disappears.
• Cytoplasm divides but no cytokinesis.

Question 17

What is the purpose of the 2nd meiotic division?

Answer 17

The purpose of the second meiotic division is to
separate the pairs of chromatids so that each gamete has only 23 chromatids (‘half X’ chromosomes).

Question 18

Prophase II

Answer 18

• New spindle forms that is flipped so horizontal not vertical
• Chromosomes move towards equator

Question 19

Metaphase II

Answer 19

Chromosomes line up at equator

Question 20

Anaphase II

Answer 20

• Centromeres divide so that each chromatid is now a separate chromosome
• New chromosomes move to opposite poles

Question 21

Telophase II

Answer 21

• Nuclear membrane forms and cytoplasm starts to divide
• Cytokinesis occurs producing 4 daughter cells with half the original number of chromosomes.

Question 22

Crossing over

Answer 22

During Prophase I matching regions on homologous chromosomes may break and then reconnect to the other chromosome.
- This is called crossing over
- The point where two chromatids cross is called
a chiasma
Results in new combinations of genes along the chromosome, and creates genetic variation between gametes.

Question 23

Three levels of stem cell potency

Answer 23

• Multipotent – most limited, sometimes called adult stem cells can give rise to different cell types within a cell lineage e.g. blood stem cells can give rise to platelets, RBCs, or WBCs but not a bone cell
• Pluripotent – can be come all cell lineages, but not the cells that form the outer layer of the blastocyst
• Totipotent – can become ANY cell, only applies to cells present after first few rounds of division after fertilisation

Question 24

What is cancer and what are tumours and their two types?

Answer 24

Cancer = uncontrolled cell division.

Tumours are an abnormal mass or tissue of cells that have divided uncontrollably. They can be classified as benign or malignant.

Benign tumours remain in one place. They can’t invade or spread to other parts of the body but they can and do press on surrounding organs.

Malignant tumours can invade other parts of the body. This is known as metastasis and is how secondary tumours form. There can be multiple secondary tumours.

Question 25

Causes of cancer

Answer 25

Lots of things can cause cancer, including genetic and environmental factors. The environmental factors are called carcinogens. Cancer usually develops after prolonged exposure to carcinogens. Examples of carcinogens include:
- UV radiation
- X-rays
- Ionising radiation
- Viruses

Question 26

4 major cancer types and their screening

Answer 26

• Cervical, pap smear every 2 years
• Prostate, Digital rectal exam, biopsy
• Bowel, faecal occult blood test
• Breast, mammograms