The Mitotic Cell Cycle

Question 1

What are chromosomes made of?

Answer 1

One very long, condensed DNA molecule

Question 2

What are the main proteins present in chromosomes and what are their functions?

Answer 2

The large positively charged globular proteins called histones, their role is to organise and condense the DNA tightly so it fits in the nucleus

Question 3

Describe structure of chromatids

Answer 3

During interphase the DNA replicates to create two identical strands of DNA called chromatids, joined by a narrow region called the centromere

Question 4

Describe sister chromatids

Answer 4

The two chromatids that make up the double structure of a chromosome are known as sister chromatids

Question 5

What are at the end of chromatids?

Answer 5

The ends of chromatids are sealed with protective structures, telomeres

Question 6

What is mitosis?

Answer 6

Mitosis is the process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent nucleus

Question 7

Explain the importance of mitosis in growth of multicellular organisms

Answer 7

The two daughter cells are clones and have the same number of chromosomes as the parent nucleus. This enables unicellular zygotes to grow int multicellular organisms. Growth may occur across the whole body of the organism or be confined to certain regions

Question 8

Explain the importance of mitosis in the replacement of damaged or dead cells

Answer 8

Cells are constantly dying and being replaced by identical cells

Question 9

Explain the importance of mitosis in asexual reproduction

Answer 9

Asexual reproduction is the production of new individuals of a species by a single parent organism- offspring are genetically identical. For multicellular organisms, new individuals grow from parent organisms and then detach

Question 10

How many steps are there in the process of mitosis and what are they named?

Answer 10

1-Prophase
2-Metaphase
3-Anaphase
4-Telophase

Question 11

Describe what occurs during prophase

Answer 11

Chromosomes condense and become visible when stained. The two centrosomes move towards opposite poles. Spindle fibres begin to emerge from the centrosomes. The nuclear envelope breaks down into small vesicles

Question 12

Describe what occurs during metaphase

Answer 12

Centrosomes reach opposite poles. Spindle fibres continue to extend from centrosomes. Chromosomes line up at the equator of the spindle so they are equidistant to the two centrosome poles. Spindle fibres reach chromosomes and attach to the centromeres. Each sister chromatid is attached to a spindle fibre originating from opposite poles

Question 13

Describe what occurs during anaphase

Answer 13

The sister chromatids separate at the centromere. Spindle fibres begin to shorten. The separated sister chromatids are pulled to opposite poles by spindle fibres

Question 14

Describe what occurs during telophase

Answer 14

Chromosomes arrive at opposite poles and begin to decondense. Nuclear envelope begins to reform around each set of chromosomes. Spindle fibres break down

Question 15

What are the different parts of the cell cycle?

Answer 15

Interphase
Nuclear division
Cytokinesis

Question 16

What are the different parts of interphase?

Answer 16

G1 + S + G2

Question 17

G1

Answer 17

The gap between the previous cell division and the S phase is G. During G1 cells make the RNA, enzymes and other proteins require for growth. At some point during this phase a signal is received telling the cell to divide again

Question 18

S

Answer 18

The DNA in the cell replicates

Question 18

G2

Answer 18

The cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired

Question 19

Nuclear Division

Answer 19

Mitosis phase (M phase)
Cell growth stops during M phase

Question 19

Cytokinesis

Answer 19

Once the nucleus has divided into 2 genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells.
In animal cells, cytokinesis involves construction of the cytoplasm between the two nuclei and in plant cells a new cell wall is formed

Question 19

What is the role of telomeres?

Answer 19

Ensures that the very ends of the DNA molecules are included in DNA replication during mitosis. This ensures no genes are lost during cell division

Question 20

What are stem cells?

Answer 20

A stem cell is a cell that can divide an unlimited number of times. The ability of cells to differentiate into more specialised cells is known as potency

Question 20

Role of multipotent adult stem cells

Answer 20

As tissues and organs develop cells become more and more specialised. Most cells gradually lose their ability to divide. However, small numbers of adult stem cells remain to produce new cells for essential processes of growth, cell replacement and tissue repair

Question 20

How does cancer occur?

Answer 20

Cancers occur when changes occur in the gene that control cell division. Cancerous cells divide divide repeatedly and uncontrollably forming a tumour