CELL DIVISION Reasons Cells Must Divide Limitation is

  • Slides: 35
Download presentation
CELL DIVISION

CELL DIVISION

Reasons Cells Must Divide • Limitation is due to relationship between volume and surface

Reasons Cells Must Divide • Limitation is due to relationship between volume and surface area of cell membrane • If membrane is stretched too large: - cytoplasm will flow out of cells movement of materials in and out of cell would not be controlled (suffocation and waste poisoning) - cell would not be able to supply enough materials needed for life - not enough RNA would be able to be produced - eventually cell would burst and die

Cell division process whereby a mother cell divides into two daughter cells

Cell division process whereby a mother cell divides into two daughter cells

Types Cell Reproduction 1. Asexual: purely cell division - no exchange of genetic material

Types Cell Reproduction 1. Asexual: purely cell division - no exchange of genetic material - daughter cells have exact genetic info as mother (identical) Ex: binary fission: unicellular organisms, bacteria Mitosis: DNA + organelles duplicated

2. sexual: joining of two reproductive or sex cells (gametes or germ cells) -

2. sexual: joining of two reproductive or sex cells (gametes or germ cells) - resulting offspring has combination of into from both sets of parents - fertilization: joining of 2 gametes to form a zygote Gamete (mom) egg + gamete (dad) sperm zygote

Chromosome Number Depending on the function of a cell, the number of chromosomes it

Chromosome Number Depending on the function of a cell, the number of chromosomes it has may differ. - somatic cells: non sex cells, contain pairs of homologous chromosomes - homologous chromosomes: two copies of each autosome, similar in size, shape, and genetic material - diploid number (2 n): full set of homologous chromosomes ex: humans corn goldfish fruit flies somatic 46 10 96 8 germ 23 5 48 4

Chromosome Number - gametes: sex cells (egg, sperm) - haploid number: half set of

Chromosome Number - gametes: sex cells (egg, sperm) - haploid number: half set of chromosomes “one set” half the diploid number (N) - zygote: fertilized egg cell resulting from joining of sex cells (2 n) ex: fruit flies 2 N = 8 N = 4 diploid haploid WHY IS IT IMPORTANT THAT GERM CELLS HAVE THE HAPLOID #

CELL DIVISION IS NEEDED FOR 1. Growth: - size of cell: makes room for

CELL DIVISION IS NEEDED FOR 1. Growth: - size of cell: makes room for new parts - number of cells is increased 2. Repair and replacement of old worn out cells **adult human body produces ~ 2 trillion cells/day**

FACTORS THAT TRIGGER CELL DIVISION - cells divide in response to external signals that

FACTORS THAT TRIGGER CELL DIVISION - cells divide in response to external signals that tell them to enter the cell cycle (proteins such as growth factors, enzymes) ex: cut in skin – produces growth factor which tells skin cell to divide until wound is filled in.

FACTORS THAT STOP CELL DIVISION 1. lack of positive external signals (proteins, enzymes, growth

FACTORS THAT STOP CELL DIVISION 1. lack of positive external signals (proteins, enzymes, growth factors) 2. contact inhibition- when cell is surrounded on all sides by other cells it will stop dividing. 3. cellular senescence- preprogrammed limit to the number of times cells can divide (dependant on cells ability to maintain integrity of its DNA) **Cells cannot grow uncontrollably** Ex: E Coli doubles size and divides every 30 minutes, in 2 days would equal the mass of the Earth

CONTROLS ON CELL GROWTH - depending on function and location of cells, growth and

CONTROLS ON CELL GROWTH - depending on function and location of cells, growth and division of cells vary ex: heart, nerves, liver cells– rarely divide (only during fetal growth) cells suspended in G 0 phase **liver cells retain ability to divide but do not – if piece of liver is removed, cells will divide until original mass is reached** - skin, digestive tract – rapid growth and division (more wear and tear on these cells) - embryonic cells – very rapid division - controls can be turned on and off ex: injury – cells stimulated to divide rapidly (healing process) as injury is healed, growth and division slows down

Chromosomes colored/body Structures located in the nucleus which are composed of strands of DNA

Chromosomes colored/body Structures located in the nucleus which are composed of strands of DNA surrounded by protein and contain genetic information - since DNA triplets control genetic information, chromosomes control heredity - genes: triplet codons of DNA - only visible during cell division - each species of organism has a specific number of chromosomes

Composition of Chromosomes 1. chromatin: less tightly coiled DNA/protein complex that makes up chromosomes

Composition of Chromosomes 1. chromatin: less tightly coiled DNA/protein complex that makes up chromosomes - composed of DNA and protein which is folded over and over again so it can fit into nucleus (otherwise too long) - DNA double helix is 1000 x longer than chromosome

Composition of Chromosomes 2. nucleosome: coiled bead like structures composed of histone proteins and

Composition of Chromosomes 2. nucleosome: coiled bead like structures composed of histone proteins and DNA - result: tightly packed chromosomes seen during cell division

Composition of Chromosomes 3. chromatids: each half of chromosome 4. centromere: area where chromatids

Composition of Chromosomes 3. chromatids: each half of chromosome 4. centromere: area where chromatids are joined

SEX DETERMINATION In humans there a total of 46 chromosomes (23 pairs) - autosomes:

SEX DETERMINATION In humans there a total of 46 chromosomes (23 pairs) - autosomes: homologous chromosomes not involved in gender determination humans: 22 pairs - sex chromosomes: determine gender one pair : XX or female XY male varies among organisms ex: grasshoppers: no Y birds, moths, butterflies: male XX female X

Karyotype Photo of metaphase chromosomes of an individual - used in prenatal testing to

Karyotype Photo of metaphase chromosomes of an individual - used in prenatal testing to help determine if there abnormalities or mutations

Karyotype

Karyotype

 • The Cell Cycle DNA and organelles must be duplicated before the cell

• The Cell Cycle DNA and organelles must be duplicated before the cell can divide Cell Cycle: period from beginning of one mitosis to beginning of next - involves growth, synthesis, growth, cell division 5 phases Interphase: phases 1, 2, 3 Mitosis: phase 4 Cytokinesis: phase 5 • Goal: to produce two genetically identical cells from one mother cell Before mitosis actually occurs there is a period between cell divisions Interphase: - time between mitosis (preparation for mitosis) - can be a very long period of time (approx. 90% of cell cycle) - usually 12 -24 hrs. in mammalian cells

Phases of the Cell Cycle 1. G 1 (gap 1) phase: cell growth and

Phases of the Cell Cycle 1. G 1 (gap 1) phase: cell growth and development - after cytokinesis, daughter cells are very small and low on ATP - uses this phase to grow and gain ATP 2. S phase (synthesis): DNA replicates - only occurs after cell is large enough and has enough ATP 3. G 2 (gap 2)phase: - S phase drains energy so cell must grow and gain energy again. - m. RNA synthesize - ATP made and used in cell division - synthesis of organelles - chromosomes doubled - centrioles divide (2 pair of protein microtubules that form spindle) 4. M phase: mitosis 5. Cytokinesis: division of cytoplasm

Safeguards During Interphase • cell cycle can be halted or stopped if growth and

Safeguards During Interphase • cell cycle can be halted or stopped if growth and duplication requirements not met • Checkpoints: key inspection points which give feedback to determine if cell can move into next phase of the cycle »

Checkpoints, cont. cell cycle anmation

Checkpoints, cont. cell cycle anmation

Uncontrolled Cell Division • Most healthy body cells grow and divide a certain number

Uncontrolled Cell Division • Most healthy body cells grow and divide a certain number of times (approx. 20 -50 X), and then die (senescence) - tumors - benign (do not metastasize) - malignant (metastasize) - cancer: uncontrolled rapid cell division - do not respond normally to cell cycle checkpoints - signals to nucleus to divide are abnormal - entire cell cycle control system is abnormal - if ca. cells stop dividing, they do not do so at normal cell checkpoints - will continue to grow and divide even when coming in contact with other cells - grow until nutrients are exhausted ……… “immortal” cancer animations

Cell Division Mitosis Process whereby materials of the parent (mother) cell’s nucleus duplicate and

Cell Division Mitosis Process whereby materials of the parent (mother) cell’s nucleus duplicate and divide into 2 equal sets to be given equally to 2 daughter cells - daughter cells and identical and carry same genetic material as mother cell Cytokenesis Process by which cytoplasm divides creating two distinct cells

Mitosis Overview

Mitosis Overview

Phases of Mitosis Detail I. Prophase - first stage that shows mitosis is starting

Phases of Mitosis Detail I. Prophase - first stage that shows mitosis is starting - longest phase (50 – 60% total time) - most events happen during this phase

A. EARLY PROPHASE 1. centrioles move to opposite poles outside nuclear membrane 2. aster

A. EARLY PROPHASE 1. centrioles move to opposite poles outside nuclear membrane 2. aster forms: protein fibers (astral rays) form around centrioles (look like stars) Centriole + astral rays aster 3. chromosomes continue to grow shorter and thicker and begin to pair up (sister chromatids – identical) 4. sister chromatids become attached a one point along the length Centromere: attaches chromosome Chromatids: half of each identical sister chromosome Chromosome 5. nucleolus disappears 6. nuclear membrane disintegrates

B. MIDDLE PROPHASE 7. centrioles form spindle by building fibers Spindle: football shaped structure

B. MIDDLE PROPHASE 7. centrioles form spindle by building fibers Spindle: football shaped structure made up of microtubule protein fibers Types of fibers: - Spindle (polar): from centriole to centriole - Traction: from centriole to equator - Kinetochore: disc shape protein found in centromere region, attaches to fibers SPINDLE APPARATUS

c. LATE PROPHASE 8. paired chromatids begin to move to equator

c. LATE PROPHASE 8. paired chromatids begin to move to equator

II. Metaphase - shortest stage: only a few minutes 1. sister chromatids line up

II. Metaphase - shortest stage: only a few minutes 1. sister chromatids line up at equator of cell 2. centromeres (kinetochore fibers) of identical chromatids attach to traction fibers that lead to opposite poles (importance of two identical chromosomes) spindle checkpoint: blocks transition to anaphase if all chromosomes not attached to spindle

III. Anaphase 1. centromeres that join sister chromatids split and they become individual chromosomes

III. Anaphase 1. centromeres that join sister chromatids split and they become individual chromosomes 2. matching (homologous) chromosomes repel each other 3. chromosomes start to move to opposite poles (centromeres are pulled by traction fibers that begin to shorten) 4. anaphase ends when chromosomes reach the poles and stop moving (mechanism still a mystery)

IV. Telophase and Cytokinesis 1. chromosomes uncoil and lengthen – become tangled mass of

IV. Telophase and Cytokinesis 1. chromosomes uncoil and lengthen – become tangled mass of chromatin (occurs where nuclei of daughter cells will form) 2. nucleolus and nuclear membrane reform (two new nuclei have formed in mitosis) 3. spindle breaks apart 4. A. animal cells: cleavage furrow forms: protein belt pinches cell membrane inward B. plant cells: cell plate forms from inside and spreads to cell wall 5. Cytokenesis occurs: cytoplasm divides - result: 2 exact duplicate cells (daughter cells) have same genetic info as mother cells

Identify the stages of mitosis

Identify the stages of mitosis

Difference in Mitosis Plant Cells Cell plate Unequal size daughter cells No centrioles (spindle

Difference in Mitosis Plant Cells Cell plate Unequal size daughter cells No centrioles (spindle formed from cell wall) Mitosis animation Virtual cell animation

IMPORTANCE OF CELL DIVISION • completion of cell cycle produces new organisms and they

IMPORTANCE OF CELL DIVISION • completion of cell cycle produces new organisms and they grow by adding more cells • if cell division ceases - unicellular organism: will die immediately - multicellular organism: will die within a few days • cell cycle ensures that life will always be able to produce more life in an organized fashion.