Cell Growth and Division

Chapter 10(M)

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

Cell Division and ReproductionAsexual ReproductionSexual Reproduction

Asexual Reproduction

Production of offspring from a single parent

Offspring is identical to parentEx bacteria, yeast, unicellular organisms & some multicellular organisms

Binary Fission Bacteria

Budding Yeast

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

The Cell Cycle

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.

MitosisDivision of the NucleusStages

ProphaseMetaphaseAnaphaseTelophase

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

Animal Cell

Plant Cell

Regulating the Cell Cycle Cell division is affected by

Cell DensityAnchorageRegulatory Proteins

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

Treatment of Cancer Surgery Radiation therapy high energy

radiation disrupts cell division Chemotherapy drugs that inhibit

cell division Side effects:

Radiation can lead to sterilityChemotherapy can cause nausea,

hair loss