cell growth and division chapter 10 p 272- 301 8/29/2015chap 10: cell growth and division 2009

Cell Growth and Division

Chapter 10P 272- 301

04/19/23 Chap 10: Cell Growth and Division 2009

Biology notes-Chapter 8 2

Cell DivisionAbout 2 trillion cells- about 25 million cells per

second- are produced by an adult human body every day. All cells come from the division of preexisting cells. (cell theory) Cell division or reproduction is the process by which cells produce offspring cells. Cell division differs in prokaryotes and eukaryotes. Cell reproduction in both prok and euk produce the same result – two cells from one!!


ReviewWhat are the three parts to the cell theory?1. All living organisms are composed of one or more

cells.2. Cells are the basic units of structure and function in

an organism.3. Cells come only from the reproduction of existing

cells.Four things common is all cells:

cell membrane, cytoplasm, DNA, ribosomes

How does a cell produce a new cell?

10.1- Why do cells Divide?10.2- How do cells Divide?10.3- How does a cell control the process of cell

division?10.4- How does a single undifferentiated cell

lead to a complex multicellular organism?


Voc Terms 10.1- 10.2


THINK ABOUT IT –Limits to Cell Size

1. When a living thing grows, what happens to its cells?

2. What is there about growth that requires cells to divide and reproduce themselves?

What are some of the difficulties a cell faces as it increases in size?

The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane.


Information “Overload”

– Living cells store critical information in DNA.

– As a cell grows, that information is used to build the molecules needed for cell growth.

– As size increases, the demands on that information grow as well. If a cell were to grow without limit, an “information crisis” would occur.


Information “Overload” – Compare a cell

to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access.

– A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.


Exchanging Materials

– Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way.

– The rate at which this exchange takes place depends on the surface area of a cell.

– The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume.

– The ratio of surface area to volume is key to understanding why cells must divide as they grow.


Ratio of Surface Area to Volume

– Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume.

– If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.


Traffic Problems– To use the town

analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out.

– Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.


Division of the Cell

– Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.

– Before cell division, the cell copies all of its DNA.

– It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA.

– Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.


Cell Division and Reproduction

How do asexual and sexual reproduction compare?

– The production of genetically identical offspring from a single parent is known as asexual reproduction.

– Offspring produced by sexual reproduction inherit some of their genetic information from each parent.


– In multicellular organisms, cell division leads to growth. It also enables an organism to repair and maintain its body.

– In single-celled organisms, cell division is a form of reproduction.

Asexual Reproduction


Asexual Reproduction

– Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them.

– Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring.

– Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

– -Bacteria cells reproduce by binary fission


Sexual Reproduction

- In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow.

– The offspring produced inherit some genetic information from both parents.

– Most animals and plants, and many single-celled organisms, reproduce sexually.



Cell Division -EukaryotesTwo main types of division:1. Mitosis- results in new cells with genetic material

that is identical to the genetic material of original cell

During: growth, development, repair, asexual reproduction (production of offspring from one parent)

2. Meiosis- occurs during the formation of gametes (reproductive cells, 1n), reduces the chromosome number by ½ in new cells, often combine to make 2n cells

Comparing Sexual and Asexual Reproduction


8.2- THINK ABOUT IT

1. What role does cell division play in your life?

2. Does cell division stop when you are finished growing?

What is the role of chromosomes in cell division?

– Chromosomes make it possible to separate DNA precisely during cell division


– The genetic information that is passed on from one generation of cells to the next is carried by chromosomes.

– Every cell must copy its genetic information before cell division begins.

– Each daughter cell gets its own copy of that genetic information.

– Cells of every organism have a specific number of chromosomes.

Chromosomes


Prokaryotic Chromosomes

– Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm.

– Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.


Eukaryotic Chromosomes

– In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.


• Chromatin is composed of DNA and histone proteins.


• DNA coils around histone proteins to form nucleosomes.


• The nucleosomes interact with one another to form coils and supercoils that make up chromosomes.



Chromosomes structure cont:• Chromosomes contain 2 identical halves each half of

the chromosome is called a chromatid• Chromatids form when the DNA makes a copy of

itself before cell division• When the cell divides each ½ gets a copy• Chromatids are attached by the centromere• When DNA is not tightly packed it is call chromatin• Prokaryotes DNA is simple, circular, one

chromosome, very compact to fit in the cell


Chromosomes Numbers

• Each species has a set number of chromosomes

Must know terms:1. Sex chromosomes: are chromosomes that

determine the sex of an organism, they may also carry genes for other characteristics (X, Y) (2 humans)

2. Autosomes- all non sex chromosomes (44 of humans )


Chromosomes Numbers cont:

3. Homologous chromosomes- they are chromosomes that are the same sex and shape and carry genes from the same traits

4. Karyotype- photomicrograph of chromosomes in a normal dividing cell found in human cells (46 chromosomes)

22 homologous pairs of autosomes2 sex chromosomes


Karyotype


Diploid (2n) and haploid (n)• If a cell is said to have 2 sets of chromosomes it is

said it is diploid• They have two sex chromosomes in animals

including animals• Except for reproductive cells like sperm and eggs or

generally called gametesEx the 2n or diploid or number of chromosomes is 46

and 22 pairsIf it is haploid it contains only one set of chromosomes

for example only has one set of the autosomes and sex chromosomes 23 total

The Cell Cycle

What are the main events of the cell cycle?

– During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells.


The Prokaryotic Cell Cycle

– The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division.

– Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size.

– When DNA replication is complete, the cells divide through a process known as binary fission.



Cell division in prokaryotes

• Have no true nuclei or membrane-bound organelles

• DNA is not coiled around proteins- it is circular attached to the inner surface of the plasma membrane like a rope attached to the inner wall of a tent

• Process of cell division is Binary fission


Binary fissionIs the division of a prok into

two offspring cells1. DNA is copied get two

identical chromosomes2. A new cell membrane then

begins to develop between the two DNA copies

3. Cell grows till its 2x the original size

4. Cells split containing identical chromosomes


Binary fission

The Eukaryotic Cell Cycle

– The eukaryotic cell cycle consists of four phases: G1, S, G2, and M.

– Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.


G1 Phase: Cell Growth

– In the G1 phase, cells increase in size and synthesize new proteins and organelles.


S Phase: DNA Replication

– In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.


G2 Phase: Preparing for Cell Division

– In the G2 phase, many of the organelles and molecules required for cell division are produced.


M Phase: Cell Division

– In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.

– Mitosis is the division of the cell nucleus.

– Cytokinesis is the division of the cytoplasm.

– Or a G0: stage in which the cell is mature and no longer dividing04/19/23 Chap 10: Cell Growth and Division 2009

What

events

occur

during

each

of the four

phases

of

mitosis?

• Division of the nucleus• Occurs during cell division• Continuous process that allows for the organized

distribution of cell’s copied DNA to offspring cells• Divided into four phases PMAT1. prophase2. metaphase3. Anaphase4. telophase


Important Cell Structures Involved in Mitosis

– Chromatid – each strand of a duplicated chromosome

– Centromere – the area where each pair of chromatids is joined

– Centrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindle

– Spindle – a fanlike microtubule structure that helps separate the chromatids


Prophase

– During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.


Prophase

– During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.

– The centrioles move to opposite sides of nucleus and help organize the spindle.


Prophase– During prophase,

the first phase of mitosis, the duplicated chromosome condenses and becomes visible.


– The spindle forms and DNA strands attach at a point called their centromere.


Prophase– During prophase, the

first phase of mitosis, the duplicated chromosome condenses and becomes visible.


– The spindle forms and DNA strands attach at a point called their centromere.

– The nucleolus disappears and nuclear envelope breaks down.


Metaphase

– During metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.


Metaphase

– During metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.

– The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.


Anaphase

– During anaphase, the third phase of mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.


Anaphase

– During anaphase, the third phase of mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.

– The chromosomes separate into two groups near the poles of the spindle.


Telophase

– During telophase, the fourth and final phase of mitosis, the chromosomes spread out into a tangle of chromatin.


Telophase


– A nuclear envelope re-forms around each cluster of chromosomes.


Telophase


– A nuclear envelope re-forms around each cluster of chromosomes.

– The spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.


Cytokinesis

How do daughter cells split apart after mitosis?– Cytokinesis completes the process of cell

division – it splits one cell into two.

– Cytokinesis is the division of the cytoplasm.

– The process of cytokinesis is different in animal and plant cells.


Cytokinesis in Animal Cells

– The cell membrane is drawn in until the cytoplasm is pinched into two equal parts., Cleavage furrow

– Each part contains its own nucleus and organelles.


Cytokinesis in Plant Cells

– In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall.

– Instead, a cell plate forms between the divided nuclei that develops into cell membranes.

– A cell wall then forms in between the two new membranes.


The Stages of the Cell Cycle


cell growth and division chapter 10 p 272- 301 8/29/2015chap 10: cell growth and division 2009

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