Human Bio- Chapter 10 Cell division

What are the phases of the Cell Cycle

G1 phase

S phase

G2 phase

M Phase

What happens during G1 phase?

first growth phase

Cell produces new proteins

Grows and carries out its normal tasks for the body

Phase ends when cell’s DNA begins to duplicate

What happens during S phase?

SYnthesis phase

DNA molecules in the cell nucleus form exact copies of themselves

What happens during G2 phase?

second growth phase

Relatively short phase

Involves preparation for cell division

What happens during M phase?

mitotic phase

Cell divides into two daughter cells

After this can go back to G1 phase or G0 phase where it stops dividing

What is meiosis?

Division of the nucleus

Each new cell must contain the same genetic material as the parent cell And meiosis ensures that each body cell receives the same hereditary information (DNA) as its parent cell

PMAT- phases

What happens during interphase?

period between nuclear divisions

Cell goes through G1, S, G2

Quantity of DNA in the nucleus doubles

What happens during Prophase?

1st stage of mitosis

Two pairs of centrioles become visible and more to opposite poles of the cells

Microtubules begin to radiate from centrioles and form to create spindle fibres

Nuclear membrane breaks down

Chromatin threads of DNA become tightly coiled and can be seen as chromosomes (condenses)

What happens during metaphase?

Chromatid pairs line up on the equator of the spindle

Spindle fibres attach to the centromere of each pair

What happens during Anaphase?

Each pair of chromatids seperate at the centromere

Chromatids are called chromosomes again, each are a single strand of chromosome

Chromosomes are then pulled away from one another towards opposite ends of the cell

Centromeres still attached to spindle fibres

What happens during telophase?

Two sets of chromosomes uncoil to become chromatin threads

Nuclear membrane re-forms around each group

Spindle fibres disappear

What is cytokenesis?

Last phase of nuclear division (occurs while during telopase)

Division of the cytoplasm is cytokenesis

How does cytokinesis occur?

Furrow develops in the cytoplasm between the teo nuclei

Furrow gradually deepens until the cytoplasm cuts into 2 parts, each with their own nucleus

What does mitosis and cytokinesis result in?

Formation of 2 daughter cells

Bác each chromosome was duplicated prior to mitosis and a copy went into each duaghter cell, each daughter cell has exactly the same number and type of chromosomes as the parent cell

Genetic info is therefor passed from parent to daughter cells without change

How can cells be classified?

Classified as either stem or specialised cells

Specialised cells are unable to divide.

When stem cells undergo mitosis, daughter cells may be new stem cells or cells that differentiate to form specialised cells

What is differentiation?

Process by which cells become specialised cells

As cells undergo division by mitosis, different genes become activiated.

This makes the cells differentiate into specialised cells that can perform particular functions

What are stem cells?

Cells tha undergo differentiation

They are not specialised for any particular role and are capable of repeated division by mitosis

How do stem cells work?

In the right conditions, stem cells can differentiate into specialised cells

They have the potential to develop into any cell type, could possibly provide an unlimited source of cells for repair of tissues

How can stem cells be classified?

Based on where they originate, or the type of cells that they can form

1. Totipotent stem cells

2. Pluripotent stem cells

3. Multi potent stem cells

What are totipotent stem cells?

Stem cells that have the potential to create any type of cell necessary for embryonic development, including the embryo itself and all the membrane associated with embryonic development

What are pluripotent stem cells?

Stem cells that can give rose to any of the cells in the body

Embryonic stem cells are pluripotent as they differentiate to form all cells of the individual

What are multipotent stem cells?

Stem cells tha have the potential to form a number of different type of cells

E.g: blood stem cells give rise to red blood cells, white blood cells and platelets.

Some examples are embryonic stem cells, adult stem cells, and cord blood stem cells are multipotent

What are gametes?

Gametes are the reproductive cells of a human, sperm for males, ova for females

How many chromosomes do humans have?

The human body contains 46 chromomes

Process of mitosis contains 46 chromosomes

What happens to the chromosome during fertilisation?

At fertilisation, the fusion of the sperm and egg results in doubling hr chromosome number, so it would be 92 chromosomes.

Sony resultant offspring would have 184 chromosomes

How come mitosis isn’t used for the production of gametes but meiosis is instead?

If mitosis were responsible for the production of gametes, chromosome numbers would double with each succeeding generation.

Meiosis results in daughter cells with half the number of chromosomes that were present in the original cell

What are haploid number and diploid cells?

Haploid number- daughter cells have half the number of chromosomes than parent cell. Humans = 23

Diploid cells- the number of chromosomes in body cells. Humans = 46

What are homologous chromosomes?

Chromosome sin diploid cells that exist in pairs that are identical in shape and carry genetic information that influence the same characteristics

What are the key stages of meiosis (3)

Interphase

First division

Second division

Meiosis has 2 divisions but the chromosomes only duplicate once

What happens during interphase (meiosis)?

Prior to undergoing meiosis, a cell grows and the DNA is replicated

DNA replication occurs the same way as in mitosis

What happens during the first division?

Homologous pairs seperate and two daughter cells form wit 23 chromosomes, each with two chromatids

What happens during the second division?

Chromatids seperate, resulting in 4 daughter cells with 23 chromosomes, each with 1 chromatid

What is are the stages of meiosis?

Prophase |

Metaphase |

Anaphase |

Telophase |

Prophase ||

Metaphase ||

Anaphase ||

Telophase ||

What happens during Prophase | ?

Chromosomes become visible as long threads, consists of a pair of chromatids

Chromosomes gradually move so the members of a pair of homologous chromosomes come to lie alongside each other throughout their entire length

Chromosomes condense, consists of 2 chromatids, each chromosome pair appears as 4 strands twist together

Nuclear membrane breaks down

What happens during Metaphse | ?

As chromosomes short and thicker, spindle forms

Paired chromosomes are arranged on the spindle fibres across the equator of the cell

What happens during Anaphase | ?

Pairs of homologous chromosomes move apart, one member of each pair moving to opposite poles

Results in 23 chromosomes moving to each pole of the cell ( therefore in first division of meiosis, number of chromosomes assembling at each pole of the cell is half the number in the original cell)

What happens during Telophase | ?

Chromosomes decondense, nuclear membrane may reform

Cytokinesis also occurs, cytoplasm dicing and cell membrane forming to produce two cells

What happens during prophase || ?

New spindle forms at each end of the original spindle, (usually at right angles to the original).

Chromosome in each cell gradually move towards the equator

What happens during metaphase || ?

Chromosomes are arranged on the new spindle

Centromeres divide, each chromatid is now a seperate chromosome

What happens during anaphase ||?

New chromosomes migrate to opposite poles of the cell

What happens during telophase || and Cytokinesis?

Nuclear membranes being to form and the cytoplasm begins to divide

What happens at the end of the 2nd division?

4 new cells have been formed, each with half the number of chromosomes of the original cell

What is the difference between Mitosis and Meiosis? (MITOSIS EDITION)

One duplication of chromosomes and one nuclear division

Produces 2 haploid cells

Homologous chromosomes do not pair

Chromatids seperate so that each new cell gets a complete set of daughter chromosomes

Chromosomes do not change their genetic make-up

Produces new cells for growth and repair

What is the difference between Mitosis and Meiosis? (MEIOSIS EDITION)

One duplication of chromosomes and 2 nuclear divisions

Produces 4 haploid cells

Homologous chromosomes S pair up

Genetic make-up of chromosomes can be changed through crossing over

Produces haploid gametes for sexual reproduction

In first meiotic division, members of homologous pairs seperate so that new cells get a haploid set of chromosomes. At 2nd division, chromatids seperate, giving 4 haploid cells

What do meiosis and mitosis have in common?

Both processes involve the replication of DNA, reduce a doubling of the number of chromosomes prior to cell division taking place

What is crossing over?

Occurs during prophase |

When homologous chromosomes are paired, chromatids may cross, break and exchange segments

The point where two chromatids cross is called a chiasmata

This results in new combination of alleles along the chromosome, called recombination

What does crossing over result in?

Creates new combinations of genes so chromosomes passed on to offspring are not exactly the same as those inherited from the parent

What is non-disjunction

Occurs during first division of meiosis When homologous chromosomes pair and then seperate. Sometimes one or more of the chromosome pairs may fail to seperate when the cell divides

In 2nd division one or more chromatids may fail to seperate

What happens to a cell if non-disjunction occurs?

Results in one of the daughter cells receiving an extra chromosome and other daughter cell lacking that chromosome

Resultant gametes will have either 24 chromosomes or 22, not the normal 23

What happens if fertilisation happens after non-disjunction?

After fertilisation with a normal gamete from the opposite sex, zygote produced will have either have 45 or 47 chromosomes

Will produce unexpected characteristics.

What happens to infants who were born with one more or less chromosome?

Such changes to the chromosome number cause sever and distinctive birth defects, and miscarriages often early in the pregnancy

What is trisomy and monosony?

Trisomy = 1 extra chromosome

Monopsony = missing a chromosome

Partial trisomy/monosomy = missing part of or having an extra part of a chromosome

What Is independent assortment?

Occurs during first division, when homologous pairs of chromosomes seperate at random.

Chromosomes move apart during the first meiotic division, do so independently. So one pair of chromosomes separating is unaffected by the way any of the other pairs seperate.

Combination of genes arranged in an order that has probably never occurred before and will probably never occur again.

What is cancer?

When cells divide uncontrollably

What is a tumour?

Uncontrolled growth of abnormal cells produces tumour or mass

Some tumours are malignant (able to spread to other parts of the body) - this is metastasis, this can cause secondary tumours to develop in areas away from the original tumour

What are benign tumours?

Tumours that are not able to invade normal tissues, blood, lymph vessels, so they do not spread to other parts of the body.

They can grow and press surrounding tissues, they can become dangerous and exert pressure on vital organs.

What are some causes of cancer

Causes of cancer = carcinogen

UV radiation from sun

X-rays emitting radiation

Ionising radiation, such as from uranium

Viruses

Chemical carcinogens like tobacco and asbestos

How do you prevent cancer?

By education (schools, advertisement)

By legislation (smoking being banned in public places)

Avoid smoking

Use sunscreen

Good diet with adequate fibre

Avoid being overweight or obese

Limit alcohol intake

Use protective clothing when handling chemicals

How do you detect cancer?

Papaniclaou / Pap test- for cervical cancer

Screening (x-ray of chest) - breast cancer

Faculty occult blood test- Bowel cancer

Digital rectal examination, prostate-specific antigen, blood test, biopsy- Prostate cancer