5 the mitotic cell cycle

What is a chromosome

Thread-like structure made of DNA

What is a Chromatid?

• one half of two identical copies of a replicated chromosomes

• MILLIONS OF NUCLEOTIDES → LENGTH OF DNA → CHROMATID

  { 1. Phosphate Group 2. Pentose Sugar 3. Nitrogenous Base }- Adenine-Thymine-Cytosine-Guanine

What is a Centronomere?

• the region of a chromosome to which the microtubules of the spindle attach via the kinetochore, during cell division.

What are Telomeres?

• protective sequence of nucleotides found at the ends of chromosomes

What are histone proteins?

• basic proteins which associate with DNA to form nucleosomes

What are chromatin?

a complex of nucleic acids (DNA and RNA) and other proteins whose primary function is to compress DNA into a compact unit which will fit inside the nucleus

What is DNA (deoxyribonucleic acid)?

DNA is the molecule of inheritance and is made up of a series of genes.

• a gene is a section of DNA that codes for one protein

• DNA molecules are in sister chromatids so that their

• genes are identical

• when cells divide, one chromatid goes into one daughter cell and the other to the other daughter cell, making the daughter cells genetically identical

• size of DNA molecule – 2nm

• the total length of DNA of 46 chromosomes of an adult human is about 1.8m, this needs to be fit into a nucleus of 6μm

• therefore, the DNA is wound around the outside of proteins called histones

• these histone proteins (and therefore, nucleosomes) condense DNA to chromatin

Outline Nucleosomes

• 11nm wide by 6nm long

• made of 8 histone molecules

What are telomeres?

• cap the ends of chromosomes and are needed for successful cell division

• permit continued replication

• prevent the loss of genes

• telomeres are made of DNA with short base sequences that are repeated multiple times

• the copying enzyme, telomerase, stops a little short of the end of DNA

• more bases are added, which don’t have useful information, but allows telomerase to complete copying the meaningful DNA

What is the cell cycle?

Processes of growth, development, and reproduction.

What is Interphase (G1 + S + G2) in the cell cycle?

• Longest phase

• Normal cell work/functions

• The cell grows to its normal size

• Time spent between cell divisions

Outline G₁ phase

• cells make RNA, enzymes and other proteins needed for growth

• at the end of G₁ phase, the cell becomes committed to dividing or not

Outline S phase

• synthesis of DNA

• the DNA in the nucleus replicates so that each chromosome consists of 2 identical chromatids: DNA replication

Outline G₂ phase

• the cell continues to grow

• new DNA is checked, and any errors are repaired

• preparations are made to start cell division e.g., a sharp increase in production of the protein tubulin is observed which is needed to make microtubules for mitotic spindle

Outline M phase (mitosis)

Nuclear division that produces 2 genetically identical daughter cells.

What are the functions of mitosis

• growth

• cell replacement

• repair of tissues

• asexual reproduction

• immune response (cloning B and T-lymphocytes)

What are the 4 Stages of mitosis

Prophase Metaphase Anaphase Telophase

Outline Prophase

• centrosomes migrate to opposite poles of mitotic spindle

• chromatin starts to condense

• nuclear envelope and nucleolus begin to disappear

• centrosomes and migrate to opposite poles of the cell

  and form poles of mitotic spindle

• asters and spindle fibres form

Outline Metaphase

• centrosomes are at poles of the cell and organise the production of spindle microtubules

• chromosomes line up across equator of the spindle

• each chromosome splits at centromere

• chromosomes start to be pulled apart by microtubules

Outline Anaphase

• chromatids move to opposite poles, centromeres are first pulled by microtubules

• spindle fibres contract and chromosomes are pulled to the opposite ends

Outline Telophase

• nuclear envelope and nucleolus reforming

• nucleus divides

• chromosomes are at poles of cell

What is Cytokinesis?

The division of cytoplasm.

Outline the process of cytokinesis in plants

• cell plate forms across equator of cell; cellulose, cell wall laid down

• cytoplasm is hence divided into 2

Outline cytokinesis in animal cells

• contractile ring forms, pushing the equator of cell inwards, forming a cleavage furrow

• this cleavage furrow deepens as active filaments in the ring contract

• eventually the cell splits into 2

What are the differences in plant and animal cell mitosis?

• plant cells don’t have any visible centriole or aster

• in plant cells, daughter cells get separated by cell

  plate, there is no cleave furrow formation

What are kinetochores?

• protein molecules which bind to DNA in centromere and microtubules

• bundles of microtubules called spindle fibres extend from kinetochores to poles of spindle during mitosis

What is a Centronomere?

• needed for separation of chromatids during mitosis

• site of attachment of spindle microtubules

• each metaphase chromosome has 2 kinetochores at its centromere and microtubules

What is a Centrosome?

• an organelle found in animal cells that acts as the microtubule organising centre (MTOC) for construction of the spindle

• present at the poles of cell

What are Stem cells?

Stem cells are cells that can divide an unlimited number of times by mitosis.

• extent of the power of a stem cell to produce different cell types is called its potency

What is Stem cell therapy?

• introduction of new adult stem cells into damaged tissue to treat a disease or injury

What is Cancer?

• a result of uncontrolled mitosis; cancerous cells divide repeatedly and form a tumour

What is a carcinogen?

• agent that causes cancer e.g., radiations (UV, X-rays), tar, nuclear fallout

Outline the cellular changes that occur in the development of cancer?

1. mutation occurs in gene responsible for cell division leading to formation of an oncogene from a proto-oncogene

2. this causes uncontrolled cell division

3. coordination of cell cycle is lost (cell does not receive/respond to signals that tell it to stop dividing)

4. loss of function and lack of specialisation occurs

5. a tumour is formed, an irregular mass of cells showing an abnormal change in shape