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Limits to Cell Size Cells grow and increase in size Upper limit to the size of a single cell If cells keep growing
More demands are placed on the DNACells becomes less efficient in moving
nutrients and wastes Cells divide before it becomes too
large
Cell Size As a cell increases in size its volume
increases faster than its surface area. Smaller objects have a greater
ratio of surface area to volume.
Purpose of Cell Division Cell division essential for life
1. Repair replacement of lost or damaged cellsSkin cells are constantly being replaced
2. Growth cells divide and increase in size, so that organism can grow
3. To maintain a favorable Surface area to volume ratio
Infant Baby Child Adult
Asexual Reproduction
Production of offspring from a single parent
Offspring is identical to parentEx bacteria, yeast, unicellular organisms & some multicellular organisms
Sexual Reproduction
Two parents are involved Genetic material from each parent
combines Offspring is different from parent
The Process of Cell Division Genetic material - packaged as DNA
is distributed to two daughter cells
mitotic chromosomeDNAchromatin
Chromosomes and Cell Division1. Chromatin fibers of DNA and
protein2. Chromosomes Chromatin fibers
condense and become visible compact structures
3. Sister Chromatids before the cell divides the DNA duplicates and forms identical copies
Prokaryotes and Eukaryotes
Prokaryotes, the genome is often a single long DNA molecule
Eukaryotes, the genome consists of several DNA molecules
DNA is passed from one generation to the next
The Cell Cycle An orderly sequence of events that
extends from the birth of a cell till the time it divides itself
All Eukaryotic cells undergo this cycle
Cycle is divided into InterphaseMitotic Phase
Interphase 90% of the Cell Cycle
1. G1(gap)phase: cell spends most of its functional life. Gap bet. DNA syn
& cell div Cell grows,
protein & organelles synthesized
Interphase 90% of the Cell Cycle
1. G1(gap)phase: cell spends most of its functional life. Gap bet. DNA syn
& cell div Cell grows,
protein & organelles synthesized
Interphase contd. S-Phase the DNA
synthesis phase. DNA molecules are
copied or replicated, single stranded DNA in G1 phase to double stranded DNA in G2.
G2 Phase completion of DNA syn. & onset of cell division
Mitotic Phase
Division of the nucleus plus cytokinesis, produces two identical daughter cells
Interphase is not part of mitosis, it encompasses stages G1, S, and G2 of the cell cycle.
InterphaseChromatin not visible DNA replicatedNew organelles are formed Cell grows by producing
proteins and cytoplasmic organelles
Prepares for cell division.
Prophase Chromosomes
condensed and visible with sister chromatids joined together
The nucleoli disappear Centrioles at opposite
poles of cell The mitotic spindle
begins to form
Phase ends with the breakdown of the nuclear membrane
Metaphase The second stage Chromosomes
gather in the a plate across the middle of the cell
Mitotic spindle is fully formed
All chromosomes are attached to the spindle microtubules
Anaphase
The third stage of mitosis
The sister chromatids suddenly separate from their partners.
Each chromatid daughter chromosomes move toward the poles
Microtubules shorten, bringing the chromosomes closer to the poles.
Telophase The final stage of mitosis The chromosomes reach the
poles of the spindle. The reverse of prophase
spindle disappears, nuclear envelopes reform, the chromosomes uncoil and lengthen, and nucleoli reappear.
Two genetically identical daughter nuclei are formed
Cytokinesis follows
Cytokinesis Division of the cytoplasm Occurs along with telophase Two daughter cells separate Difference in animal and plant cells
Animal Cell cell membrane pinches off to form a cleavage furrow
Plant Cell Cell plate is formed to divide cell into two
Density dependent inhibition
Cultured cells normally divide until they form a single layer on the inner
surface of the culture container
If a gap is created, the cells will grow to fill the gap.
Anchorage dependence
Cells must be anchored to a substratum, typically the extracellular matrix of a tissue.
Cancer cells are free of both density-dependent inhibition and anchorage dependence.
Regulatory Proteins
Cyclins timing of the cell cycle Regulatory proteins
InternalExternal growth factors
Fluctuates during cell cycle
Growth Factors Coordination between cells
protein signals released by body cells that stimulate other cells to divide
Body has many different types Each stimulates only cells with that
type of receptor
Apoptosis
Programmed cell death Apoptotic cells shrink in size, break
into smaller pieces called apoptotic bodies that other body cells recognize and eat.
What Causes Cancer? Cells do not have a properly
functioning “cell cycle” control system
Cells divide excessively and result in an abnormal mass of cells
tumor-suppressor genes gene p53 inhibits cell division if switched “OFF” can cause cancer
Growth Factors and Cancer Growth factors can create cancers
proto-oncogenes normal growth factor genes that become
oncogenes (cancer-causing) when mutated
stimulates cell growth if switched “ON” can cause cancer example: RAS (activates cyclins)
tumor-suppressor genes inhibits cell division if switched “OFF” can cause cancer example: p53
Tumors and Cancer Benign mass of normal cells
Can be removed surgicallyAlways remain at their original site
MalignantMass of cancer cellsSpread to other tissues by entering
the circulatory system Metastasis spread of cancer
cells beyond site
Types of Cancer Carcinoma external or internal
coverings of the body-skin, intestinal linings
Sarcoma bone and muscle Leukemia and Lymphoma- blood
forming tissues