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Unit 8: The Cell Cycle. Why do Cells Divide? . To make copies of cells for growth (you started out as 1 cell, today you have around 10 trillion) . Why do cells divide?. To make copies of cells for repair (cells wear out and need to be replaced). Why do cells divide? .

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why do cells divide
Why do Cells Divide?

To make copies of cells for growth (you started out as 1 cell, today you have around 10 trillion)

why do cells divide1
Why do cells divide?

To make copies of cells for repair (cells wear out and need to be replaced)

why do cells divide2
Why do cells divide?

To carry on the species – during ASEXUAL reproduction organisms undergo MITOSIS to make exact copies of themselves to create offspring.

During SEXUAL reproduction two gametes (egg and sperm) get together to create offspring. Gametes are made through a process called MEIOSIS.

chromosomes
Chromosomes

In eukaryotic cells, the genetic information that is passed from one generation of cells to the next is carried by chromosomes.

Chromosomes are made up of DNA.

chromosomes1
Chromosomes

Chromosomes are not visible in most cells, except for during cell division. At the beginning of cell division, chromosomes condense and become visible.

chromosomes2
Chromosomes

Before cell division, each chromosome is replicated (remember DNA replication).

Because of this each chromosome is made of 2 identical “sister” chromatids.

chromosomes3
Chromosomes

When the cell divides the “sister” chromatids separate from each other. One chromatid goes to each of the two new cells.

chromosomes4
Chromosomes

Each pair of chromatids is attached at an area called the centromere (usually in the middle of the chromatids)

chromosomes5
Chromosomes

Humans have 46 chromosomes. There are 23 pairs. 23 chromosomes come from their father and 23 from their mother.

2 of the chromosomes are sex chromosomes (represented by an X and Y).

the cell cycle
The Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide.

During the cell cycle a cell:

grows,

prepares for division

(copies organelles),

and divides to form two new “daughter” cells.

4 phases of the cell cycle
4 Phases of the cell cycle
  • G1 Phase – cells grow, make proteins and organelles
  • S Phase – (longest phase) Chromosomes are replicated and new DNA is made.
  • G2 Phase – (shortest) organelles are duplicated
  • M Phase – cells undergo mitosis and cytokinesis
slide13

Interphase - the non-dividing part of the cell cycle, and it consists of G1 phase, S phase, and G2 phase.

slide14

Cyclins – a group of proteins that regulates when a cell should divide.

Cancer cells do not respond to the signals that regulate the growth of cells.

mitosis
Mitosis

Mitosis – cell division in eukaryotic cells that creates two identical daughter cells that are diploid (2N).

Diploid – the cells have two sets of chromosomes (example: humans have 46 chromosomes, 23 pairs)

mitosis1
Mitosis

Interphase

The cell grows and replicates its DNA, organelles, and centrioles

mitosis2
Mitosis

Step 1: Prophase

The chromatin condenses into chromosomes.

The centrioles separate, and a spindle begins to form.

The nuclear envelope breaks down.

mitosis3
Mitosis

Step 2: Metaphase

The chromosomes line up across the center of each cell.

Each chromosome is connected to a spindle fiber at it’s kinetochore (part of the centromere)

mitosis4
Mitosis

Step 3: Anaphase

The sister chromatids separate into individual chromosomes and are moved apart.

mitosis5
Mitosis

Step 4: Telophase

The chromosomes gather at opposite ends of the cell and lose their shapes.

Two new nuclear envelopes will form.

mitosis6
Mitosis

Cytokinesis

In animal cells a cleavage furrow pinches the cytoplasm into 2 new cells.

In plants a cell plate forms to divide the cells.

2 identical diploid daughter cells are formed.

mitosis7
Mitosis

P – Prophase – Prepare

M

A

T

mitosis8
Mitosis

P

M – Metaphase – Meet in middle

A

T

mitosis9
Mitosis

P

M

A – Anaphase – Apart

T

mitosis10
Mitosis

P

M

A

T – Telophase – Two new nuclei

differences between mitosis and meiosis
Meiosis Differences between Mitosis and Meiosis

Mitosis

  • Occurs in somatic (body) cells
  • Produces identical daughter cells
  • Makes 2 diploid (2N) cells
  • No crossing over
  • Occurs in germ (sex) cells
  • Produces gametes (eggs and sperm)
  • Makes 4 haploid (1N) cells
  • Crossing over occurs
amniocentesis
Amniocentesis
  • Having abnormalities in chromosomes can be devastating so…
  • _________________OR amniotic fluid test

Amniocentesis

  • Medical procedure used in ________ diagnosis of ________ abnormalities and fetal infections
  • - A small amount of ________ fluid, (which contains fetal tissues) is extracted from the amniotic sac surrounding a developing fetus
  • - The _____ _____is examined for genetic abnormalities (using a karyotype)

prenatal

genetic

amniotic

fetal DNA

human chromosomes
Human Chromosomes

46chromosomes

23 pairs

  • Humans have ___ ______________… _______
  • 2 are called sex chromosomes… X and Y
  • __________

Karyotype

  • Karyotype is a test to identify and evaluate the size, shape, and number of _________________ in a sample of body cells
  • _______, missing, or ___________ positions of chromosome pieces can cause problems with a person's growth, development, and body functions.

chromosomes

Extra

abnormal

slide30

________ Cell = Body cell

Somatic

ex: hair, blood, skin

diploid

46 chromosomes = ____ = _______

2N

slide31

________ = Sex cell

Gamete

ex: sperm (males), eggs (females)

haploid

1N

23 chromosomes = __ = _______

slide32

The Cell Cycle is the series of events that cells go through as they _________ and __________.

grow

divide

  • During the cell cycle the cell:
  • prepares for division (copies_____________)
  • _________to form two daughter cells

grows

organelles

divides

There are 4 phases:

  • 1. ___ phase – cells grows,
  • makes proteins and
  • organelles
  • 2. __ phase – (longest)
  • synthesize DNA, replicate
  • chromosomes
    • ___ phase – (shortest) organelles duplicated
    • 4. ___ phase – Mitosis and Cytokinesis

G1

S

Interphase

G2

M

meiosis
Meiosis

Meiosis – cell division that creates 4 different daughter cells that are gametes (sex cells).

meiosis1
Meiosis

Each gamete created is haploid (1N), it only contains one set of chromosomes.

In humans, the gametes (sperm and egg) each contain 23 chromosomes.

When fertilization occurs, then the resulting cell has 46 chromosomes (23 from the sperm and 23 from the egg).

meiosis 1
Meiosis 1

Prophase 1

Each chromosome pairs with its matching homologous chromosome to form a tetrad.

Crossing over occurs between the chromatids.

meiosis 11
Meiosis 1

Metaphase 1

The homologous chromosomes line up in the middle. Spindle fibers attach to each of the homologous chromosomes.

meiosis 12
Meiosis 1

Anaphase 1

The spindle fibers pull the homologous chromosomes towards the opposite ends of the cell.

meiosis 13
Meiosis 1

Telophase 1 and Cytokinesis

Nuclear membranes form.

The cell separates into two new cells.

meiosis 2
Meiosis 2

Prophase 2

The chromosomes condense and become visible.

NO crossing over occurs.

meiosis 21
Meiosis 2

Metaphase 2

The chromosomes line up in the middle.

meiosis 22
Meiosis 2

Anaphase 2

The sister chromatids separate and move to opposite ends of the cell.

meiosis 23
Meiosis 2

Telophase 2 and Cytokinesis

Meiosis 2 results in four daughter cells that are haploid (1N)

definitions
Definitions

Tetrad – four sister chromatids (2 homologous chromosomes) that match up with each other during prophase 1.

definitions1
Definitions

Crossing over – When homologous chromosomes switch part of their chromatids. Results in genetic variation.

slide45

Homologous chromosomes: chromosomes with the same genes as each other, in the same sequence, but do not necessarily have the same allele of those genes.

slide46

Homologous chromosomes pair up with one another, forming a tetrad (4 chromatids) during prophase I.

crossing over
Crossing Over
  • A process occurring during meiosis wherein two homologous chromosomes pair up and exchange segments of their genetic material.
slide48

This occurs at the stage when chromatids of homologous chromosomes pair up during synapsis, forming a tetrad. The chromatids form X-like structures (chiasma or chiasmata). They break into segments, which are then exchanged with one another.

slide49

Crossing over is important because it results in new combinations of genes that are different from either parent, contributing to genetic diversity (why you look different than your parents & siblings)

non disjunction
NON-DISJUNCTION
  • When the chromosomes do not separate properly during meiosis (either in in anaphase I or in anaphase II).
  • This leads to the production of gametes that have the wrong number of chromosomes.
slide51

When a zygote is formed from the fertilization of a gamete with an extra chromosome, three chromosomes of one type are present instead of two (Ex: Down syndrome (trisomy 21, 47 chromosomes) Klinefelter’s Syndrome in males ( XXY, 47 chromosomes)

slide52

When a zygote is formed from the fertilization of a gamete with one less chromosome, 1 chromosome is present instead of two (monosomy) ( ex: Turner’s Syndrome in females (XO, 45 chromosomes)