Chapter 9Cell Reproduction

Review:What we know

• Cells have DNA / genetic information

• We pass on our info to our children

• All our cells contain DNA

• Chromosomes are bundles of DNA

What we need know

• How do our cells make new cells?

• What can go wrong?

• Do all cells get made the same?

• Can do bacteria and viruses make new cells?

In the beginning…

• You start life as a single cell

Human Embryo Day 3

Human Embryo 20 Weeks

Until the end of time…

• New cells made throughout entire life

• Called cell reproduction

Cell Reproduction• Goal:

– Replace old or worn out cells

– Growth & Development

• Most cells are less than 100 micrometers

–Smaller than a period . at the end of a sentence!

• Why?

–To ensure that the needs of the cell are met.

http://learn.genetics.utah.edu/content/begin/cells/scale/

Cell Size

• Factors that influence cell size are:

–Ratio of surface area to volume

• Surface area is the area covered by the plasma membrane

(nutrients & wastes

must pass through)

SA = L x W x # sides

Cell Size Continued:

• Volume is the space taken by the inner contents of the cell (including organelles and nucleus)

V = L x W x H

Cell Size Continued:

• As cell grows the ratio of surface area to volume will continue to decrease!

• Volume increases much more rapidly than the surface area!

Cell has TROUBLE:

- supplying nutrients

- expelling waste products

Cell Size Continued:

• SMALL cells have a higher ratio & can sustain themselves!

REMEMBER:

How do substances move in a cell?

Cell Size Continued:

• Communication breaks down over long distances!

Cell Size Continued:

Investigate Cell Size:

• Complete the Investigation

of Cell Size by creating a

table on your

handout.

Hypothetical Cells

SA V SA:V

Ratio

0.00002 m

0.001 m

2.5 m

30 cm

15 m

Investigation of Cell Size:

So based on your calculations do cells become large?

Are large organisms large because they contain extra large cells or just more standard – sized cells?

Cell Cycle

AKA A Cell’s

Life

• Once cell reaches a certain size it must:–Stop growing or–Divide

• The cell cycle is a cell’s cycle of growing and dividing.

• One complete cycle produces two cells.

Cell Cycle

• When repeated continuously the result is a continuous production of NEW cells!

Cell Cycle

• Interphase

– Cell grows, carries our cellular functions, & replicates (makes copies) of DNA

• Mitosis

– Cell’s nucleus and nuclear material divide

• Cytokinesis

– Cell’s cytoplasm divides creating a new cell

3 Main Phases of Cell Cycle:

• Divided into 3 stages:– G1

• Cell grows, carries out normal cell functions, prepares to replicate DNA.

• Checkpoint for size & nutrients!

Interphase:

–S (aka the synthesis phase)

• Cell copies (replicates)

its DNA to prepare for

cell division

Interphase continued:

–G2

• Cell prepares for the division of its nucleus

• Checkpoint to make sure cell is ready for mitosis!

Interphase continued:

M Phase of Cell Cycle a.k.a. Mitosis

• Result = two identical cells• Forms all human body cells • Ex: skin, blood,

bones, stomach• Slows with age

Different Forms of DNA:

• Remember DNA is found in the nucleus

• DNA Deoxyribonucleic Acid• In it’s normal state DNA is

loosely coiled and in the form of chromatin.

Chromatin:

• Looks like loose spaghetti!

• During what phase is DNA replicated? “S” phase of Interphase.

• Humans have 46 chromosomes or 23 pairs:–23 from mom–23 from dad

Chromosomes:

• Once copied the DNA will begin to coil tightly around proteins and is now called chromosomes.

Chromosomes:

Chromatid (s):

• The chromosomes 1-23 from mom will then pair up with chromosome 1-23 from dad respectively!

• Once chromosomes are paired they are now called sister chromatids.

• Each half is a chromatid but together they are sister chromatids.

Chromatid (s):

Chromatid

Chromatid

Centromere:

• Each sister chromatid is held together by a centromere!

Remember Before Cells Divide

• DNA replication occurs chromosomes double

• This stage of the cell cycle is called interphase

Interphase

• Longest stage of cell cycle

• Cell is preparing for mitosis

• Cell gets larger & centrioles double

Interphase

Interphase (cont.)

Plant Cells in Interphase

Plant Cell in Interphase (cont.)

Stages of Mitosis

P – M – A – T

PROPHASE• Chromosomes shorten & thicken

(shaped like an X)–Each half = chromatid–Attached by centromere.

• Nuclear membrane breaks down• Centrioles move apart• Spindle fibers form between centrioles

Prophase

Plant Cell in Early Prophase

Plant Cell in Late Prophase

METAPHASE• Centrioles move to opposite

sides of cell

• Spindle fibers stretch between centrioles

• Chromosomes line up in the middle by fibers connected to the centromere

• Sister chromatids are pulled to line up at center of cell

• “Meta-” Prefix meaning middle

METAPHASE (cont.)

Centromere

• Part that holds chromosomes together

Plant Cell in Metaphase

Plant Cell in Metaphase

ANAPHASE• Sister chromatids are

pulled apart• Fibers pull

chromatids toward centrioles

Anaphase

Plant Cell in Anaphase

Plant Cell in Anaphase

TELOPHASE

• Fibers begin to disappear

• Nuclear membrane begins to reform

• Cell membrane pinches in

Plant Cell in Telophase

Cytokinesis• Last stage of cell

cycle • Process of

dividing the cytoplasm

• Starts during anaphase finishes after telophase

In the end…

• Each cell has a complete set of chromosomes

• Two identical daughter cells formed from one parent cell

Mitosis Completed

http://www.edumedia-sciences.com/en/a70-mitosis

Changes in Rate of Mitosis

• Cancer: Cells divide at a fast rate out of control

•Malignant: dangerous

•Benign: not dangerous

Abnormal Cell Division

• A tumor is a mass of tissue that results from excessive cell division

Apoptosis:• Not every cell is destined to survive!• Some cells go through programmed

cell death called apoptosis. –Cell shrinks & shrivels

All animal cells have a “death program” that can be activated.

• Discovered in 1998

• Unspecialized cells that can develop into specialized cells under the right conditions.

• Two types:– Embryonic stem cells– Adult stem cells

Stem Cells

How other cells divide

1.Bacteria (Prokaryote)One cell splits into two

Asexual reproduction

Same genes as “parent”

Bacteria Cell Reproduction

How other cells divide (cont.)

2.Viruses – Inject their DNA into other cellsNot considered “living” cells

Viral Cell Reproduction

Step 3

Step 2Step 1

Step 4