CELLULAR REPRODUCTION

Chapter 9PPT corresponds to guided notes with text –

rev 3/2011

SECTION 9.1 – CELLULAR GROWTH

There is a limit to cell size….just as there is a limit to the size of living things

CELL SIZE LIMITATION THERE IS A LIMIT TO CELL SIZE!

The key(main) factor that limits the size of a cell is…

the ratio of its surface area to its volume

Surface area = area covered by the plasma/cell membrane Volume = the space taken up by the inner contents

As the cell grows its…. VOLUME increases MORE RAPIDLY than the surface area ….

so…the surface area to volume ratio decreases

This means…the cell might have difficulty supplying nutrients and expelling wastes

By remaining small…cells have a higher ratio of surface area to volume and can sustain themselves more easily.

Cells remain small to maximize…. the ability of diffusion to transport nutrients and wastes

Small cells maintain…. more efficient transport systems

Cell size also affects the ability of a cell to…communicate instructions for cellular functions

The smaller the cell the more efficient it will be!

THE CELL CYCLE

Once a cell reaches its size limit (maximum) something must happen...

either….they divide or die)!

Most cells will….eventually divide

When a cell divides it is called… CELL DIVISION or CELL REPRODUCTION

CELL DIVISION does 2 things…not only …prevents the cell from becoming too large but it also…is the way the cell reproduces

THE CELL CYCLECells reproduce by a cycle of growing and dividing

called the… CELL CYCLE each time a single cell goes through one

complete cycle it becomes…. 2 cells when the cell cycle is repeated again and again,

the result is ….a continuous production of new cells

there are 3 main stages of the cell cycle: interphase, mitosis, cytokinesis

THE CELL CYCLE

Interphase – the cell grows, carries out cellular functions and copies its DNA

Mitosis – the cell’s nucleus and nuclear material divide

Cytokinesis – the cell’s cytoplasm divides, creating a new cell

DURATION OF THE CELL CYCLE…VARIES…

depending on the (type) of cell that is dividing….

some eukaryotic cells might complete the cycle in as few as 8 minutes, others might take up to 1 year

for most normal, animals cells, the cell cycle takes approximately 12-24 hours

INTERPHASE…the stage during which…. the cell…grows and develops into a mature,

functioning cell replicates/duplicates (makes copies) …of its

DNA (genetic material) is divided into 3 stages/phases – G1, S, G2

G1 (or Gap 1) is the period….immediately after a cell

divides during G1…A cell is growing, carrying out

normal cell functions and prepares to replicate DNA

some cells, such as muscle and nerve cells, exit the cell cycle at this point and do not divide again

S (or Synthesis) is the period when the cell copies its DNA in

preparation for cell division chromosomes – structures that contain the

genetic material chromatin – relaxed form of DNA in the cell’s

nucleus the cell also takes inventory and makes sure

it is ready to continue

G2 (or Gap 2) follows the S stage and is the period when

the cell prepares for the division of its nucleus

When interphase (G1, S, G2) is completed, mitosis and

cytokinesis will follow!

PROKARYOTIC CELLS - BACTERIA, DO NOT UNDERGO CELL DIVISION IN THE SAME WAY AS EUKARYOTIC CELLS

prokaryotic cells reproduce by Binary Fission….

1. single, circular chromosome (of DNA)

copies itself

2. the cell splits into 2 cells

EUKARYOTIC CELL DIVISION – 2 TYPES

MITOSIS – makes…. 2 cells body (somatic) cells maintains the chromosome # diploid cells (2n) cells are genetically identical used for growth, maintenance

and repair Involves a cell cycle

MEIOSIS – makes… 4 cells sex (germ) cells reduces the chromosome # by ½ haploid cells (n) cells are genetically different used for the production of new

individuals DOES NOT invovle a cell cycle

PLOIDY – refers to the number of complete sets of chromosomes in a cell

DIPLOID CELLS (2n) have 2 complete sets of chromosomes – one set from each parent somatic (body) cells are diploid

HAPLOID CELLS (1n) contain only 1 set sex cells (sperm and egg) are haploid

POLYPLOID CELLS – contain more than 2 sets common in plants, fatal in animals

9.2 – MITOSIS AND CYTOKINESIS

Key activity of mitosis = accurate separation of the cell’s replicated DNA

Mitosis results in 2 “daughter” cells that are GENETICALLY IDENTICAL

WHY DO MULTICELLULAR ORGANISMS USE MITOSIS?

to increase the number of cells – growth to replace damaged cells – maintenance and

repair

4 STAGES OF MITOSIS - PMAT

ProphaseMetaphaseAnaphaseTelophase

When a cell is not dividing, the DNA is present in strands called CHROMATIN

Before cell division, the…DNA will replicate

(copy itself)and begin to condense (become more compact)

Eventually ,this will form…double-stranded CHROMOSOMES

(rod-like structures)

A DOUBLE-STRANDED CHROMOSOME HAS….

2 identical parts called (sister) chromatids …..

held together by a centromere (protein disc)

PROPHASE chromatin tightens and forms (double stranded)

chromosomes – composed of 2 “sister” chromatids spindle apparatus forms nuclear membrane begins to break down and

disappear

METAPHASE chromosomes (sister

chromatids) are pulled toward the center (equator) of the cell

ANAPHASE

Chromosomes (sister chromatids) are pulled apart and move toward the poles of the cell

TELOPHASE single stranded chromosomes arrive at the poles and

begin to relax into chromatin nuclear membrane reforms (around 2 distinct nuclei) 2 identical sets of genetic material are in the cell

WHY IS MITOSIS NECESSARY?

3 reasons…..

Growth – adds new cells Repair – of damaged tissues and parts Maintenance – cells are always dying

and need to be replaced

HOW IS MITOSIS DIFFERENT AS WE AGE?

Mitosis occurs very quickly during the early stages of life… just think we start out as one cell, a fertilized egg (zygote) and within 10 months we weigh 6,7, or 8 pounds – whew

Mitosis continues to occur fairly rapidly as we grow, however, in adulthood and into old age the process slows.

CYTOKINESIS

division of the cell and its contents into 2 “daaughter” cells

Cytokinesis results in 2 cells…each genetically identical

Cytokinesis differs in animal and plant cells

CYTOKINESIS IN ANIMAL CELLS

the cell membrane pinchesin and separates the dividingcell using a cleavage furrow

CYTOKINESIS IN PLANT CELLS

A cell plate forms along the equator (of the cell) and separates the cell into 2 cells

A new cell wall will form on either side of the cell

PROCESS OVERVIEW

THIS MAY HELP…

Interphase I - InterludeProphase P - PrepareMetaphase M - MeetAnaphase A - ApartTelophase T -TearCytokinesis C - Complete!

LET’S PRACTICE..

NAME THE STAGES OF MITOSIS…

NAME THE PHASES OF MITOSIS…

PLANT OR ANIMAL CELLS?MITOTIC PHASE?

PLANT OR ANIMAL CELLS?MITOTIC PHASE?

LET’S PRACTICE…

PLANT OR ANIMAL CELLS?MITOTIC PHASE?

ONE MORE TIME…

9.3 - CELL CYCLE REGULATION

NORMAL CELL CYCLE the TIMING and RATE of cell division is important The RATE OF DIVISION - depends on type of cell

CYCLINS (proteins) – help regulate the cycle there are built in “check points” that monitor the

cycle and stop it if needed

ABNORMAL CELL CYCLES….

CancerApoptosisStem Cells

CANCER

uncontrolled growth and division of cells cancer cells grow and divide

UNCONTROLLED cancer is due to A FAILURE TO REGULATE THE CELL CYCLE

CANCER

carcinogens are -- CANCER CAUSING AGENTS

UV radiation – THE MORE RADIATION THE

GREATER THE RISK the risk of cancer INCREASES WITH AGE

MASSES OF CELLS ARE CALLED TUMORS

Malignant Tumors (CANCER) invade and destroy nearby

tissues are life-threatening are severe and become

progressively worse

Benign Tumors do not invade other tissue are not life-threatening

APOPTOSIS

PROGRAMMED CELL DEATH – not every cell is destined to survive

Cells going through apoptosis shrink and shrivel in a controlled process

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

Helpful because ….it can help protect organisms from developing cancerous growths

2 examples: fingers and toes leaves

STEM CELLS

Are unspecialized (“blank”)cells – that can develop into specialized cell types

2 basic types of stem

cells: Embryonic Stem Cells Adult Stem Cells

WHAT IS SPECIAL ABOUT STEM CELLS?

Have the ability to renew themselves and develop into many different cell types

have potential medical uses in disease treatment because they are not specialized in structure and function

EMBRYONIC STEM CELLS

taken from an embryo (early stage of fetal development)

embryo = up to 8th week of development

can differentiate into various cell types (and therefore have greater potential for medical applications)

ADULT STEM CELLS

taken from the tissues of a growing human the term “adult” is misleading because even infants have

“adult” stem cells “adult” stem cells act as a repair system for the body,

replenishing specialized cells and maintaining the regeneration of some tissues and organs

found in bone marrow - also believed to be in brain and heart

not able to differentiate into all cell types (therefore, less potential for medical applications)

ADULT STEM CELLS

USES OF STEM CELLS repair of damaged or degenerating tissues

Parkinson's disease, Ischemic heart disease, genetic disorders, diseases of degeneration, endocrine abnormalities, neurodegenerative diseases, congenital disorders, spinal cord injuries and paralysis, and others