c ellular r eproduction chapter 9 ppt corresponds to guided notes with text – rev 3/2011
TRANSCRIPT
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