Cellular Reproduction Ch 11 Cell Cycle Cells reproduce

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Cellular Reproduction Ch 11

Cellular Reproduction Ch 11

Cell Cycle ▪ Cells reproduce by growing and dividing during the cell cycle ▪

Cell Cycle ▪ Cells reproduce by growing and dividing during the cell cycle ▪ The cell’s DNA is copied in preparation for division to ensure that the two new cells each have an exact copy of the DNA ▪ Cells of all multicellular organisms use this process, and therefore one generation of cells is linked to the next, allowing for the continuity of life

Cell Cycle ▪ Cell division prevents the cell from becoming too large. –Cells have

Cell Cycle ▪ Cell division prevents the cell from becoming too large. –Cells have an optimal size, if it’s too large, it will have difficulty supplying nutrients and expelling waste. –Cell division is also how the cell reproduces, replaces other cells, grows, and heals

Cell Cycle ▪ Cell Cycle: a series of events from the time a cell

Cell Cycle ▪ Cell Cycle: a series of events from the time a cell forms until its cytoplasm divides ▪ Multiplication by division ▪ 3 Main Stages: –Interphase, Mitosis, Cytokinesis

Cell Cycle ▪ A typical cell spends most of its life in interphase, in

Cell Cycle ▪ A typical cell spends most of its life in interphase, in which it roughly doubles the number of its cytoplasmic components, and replicates its DNA ▪ Three stages of interphase –G 1[metabolic activities]: cell is growing, carrying out normal cell functions, and preparing to replicate DNA. Occurs immediately after the cell divides. –S [DNA synthesis]: cell copies DNA in preparation for cell division. –G 2 [protein synthesis]: cell prepares for division of its nucleus.

Cell Cycle ▪ Mitosis: Process that divides the nucleus of one cell into two

Cell Cycle ▪ Mitosis: Process that divides the nucleus of one cell into two nuclei ▪ Mitosis produces two descendant [daughter] cells, each with the same number and type of chromosomes as the parent – IDENTICAL COPIES! ▪ Mitosis MAINTAINS the chromosome number

Cell Cycle ▪ Homologous Chromosomes: chromosome pairs of the same length, same centromere position,

Cell Cycle ▪ Homologous Chromosomes: chromosome pairs of the same length, same centromere position, and control the same inherited trait ▪ At the start of interphase, chromosomes are unduplicated, by the end of G 2, each chromosome has two doublestranded DNA molecules [sister chromatids]

Cell Cycle ▪ During mitosis, the sister chromatids are pulled apart –Each sister chromatid

Cell Cycle ▪ During mitosis, the sister chromatids are pulled apart –Each sister chromatid ends up in separate nuclei that are packaged into separate cells

Cell Cycle ▪ Whether or not a cell divides is determined by mechanisms of

Cell Cycle ▪ Whether or not a cell divides is determined by mechanisms of gene expression control –“Brakes” on the cell cycle normally keep the vast majority of cells in G 1 –“Checkpoint genes” monitor the completion of DNA copying, DNA damage, and nutrient availability ▪ Before mitosis the chromosomes are loosened to allow transcription and DNA replication during interphase, during mitosis the cell grows during various phases

Spindle Fibers ▪ Most animal cells have a structure called a centrosome – a

Spindle Fibers ▪ Most animal cells have a structure called a centrosome – a region of dense cytoplasm that contains a pair of centrioles ▪ These are copied during prophase, and a copy moves to each side of the cell ▪ Microtubules begin to assemble and form a spindle, which is a temporary structure that moves chromosomes during nuclear division ▪ What would happen if a cell had faulty spindles?

Mitosis ▪ Prophase –Chromosomes condense –Centrosomes move to the opposite end of cell and

Mitosis ▪ Prophase –Chromosomes condense –Centrosomes move to the opposite end of cell and microtubules begin to assemble and lengthen, forming a spindle –Nuclear envelope breaks up –Sister chromatids are attached to opposite centrosomes

Mitosis ▪ Metaphase –chromosomes are aligned midway between spindle poles –Ensures there accurate copies

Mitosis ▪ Metaphase –chromosomes are aligned midway between spindle poles –Ensures there accurate copies of the chromosomes ▪ Anaphase –sister chromatids separate and move toward opposite spindle poles ▪ Telophase –chromosomes arrive at opposite spindle poles and decondense; two new nuclei form

Cytokinesis ▪ Cytokinesis: division of cytoplasm ▪ In most eukaryotes, cytokinesis occurs between late

Cytokinesis ▪ Cytokinesis: division of cytoplasm ▪ In most eukaryotes, cytokinesis occurs between late anaphase and the end of telophase ▪ The process of cytokinesis differs between plant and animal cells

Cytokinesis ▪ Typical animal cells pinch themselves in two after nuclear division ends –Cleavage

Cytokinesis ▪ Typical animal cells pinch themselves in two after nuclear division ends –Cleavage furrow (indentation) forms ▪ Dividing plant cells face a challenge because a cell wall surrounds their plasma membrane –Disk-shaped structure called the cell plate forms and eventually partitions the cytoplasm –The cell plate forms into two new cell walls

Interphase Prophase Metaphase Anaphase Telophase Cytokinesis I Pray More At The Church!

Interphase Prophase Metaphase Anaphase Telophase Cytokinesis I Pray More At The Church!

Cancer ▪ In a normal cell cycle, different cyclin/CDK (proteins) combinations signal activities throughout

Cancer ▪ In a normal cell cycle, different cyclin/CDK (proteins) combinations signal activities throughout the cycle ▪ Mutations in these checkpoints can cause a loss of function, and if enough checkpoints fail, a cell loses control over its cell cycle –Interphase may be skipped – division occurs over and over with no resting period –Signaling mechanisms that cause abnormal cells to die may stop working

Cancer ▪ Tumor: accumulation of abnormally dividing cells ▪ Cancer: disease that occurs when

Cancer ▪ Tumor: accumulation of abnormally dividing cells ▪ Cancer: disease that occurs when there is uncontrolled division and growth of cells ▪ Malignant cells enter the bloodstream and spread to other parts of the body ▪ Lifestyle choices can reduce one’s risk of acquiring mutations –Do not smoke, avoid sun exposure

Telomeres ▪ Telomeres: noncoding repeat DNA sequences (repeated thousands of times) found at the

Telomeres ▪ Telomeres: noncoding repeat DNA sequences (repeated thousands of times) found at the ends of eukaryotic chromosomes –provide a buffer against the loss of more valuable internal DNA ▪ Telomeres shorten with every cell division and when they are too short, checkpoints halt the cell cycle and cell death soon follows –Keeps “uncontrolled” cells from overrunning the body

Stem Cells ▪ Stem cells are able to reproduce indefinitely and continuously produce enzymes

Stem Cells ▪ Stem cells are able to reproduce indefinitely and continuously produce enzymes called telomerases –These reverse telomere shortening that occurs after DNA replication ▪ Embryonic Stem Cells: After fertilization, the resulting mass of cells divides repeatedly until there about 100– 150 cells. –These cells are not specialized

Stem Cells ▪ Adult Stem Cells: Found in various tissues in the body and

Stem Cells ▪ Adult Stem Cells: Found in various tissues in the body and might be used to maintain and repair the same kind of tissue. When these mutate cancer occurs. –Less controversial because the adult stem cells can be obtained with the consent of their donor ▪ Induced pluripotent stem cells: Man-made stem cells. These are created using any cell from an organism. –In humans, a persons skin cell is removed and exposed to chemicals that turn them back into embryonic stem cells.

Differentiation ▪ Though our many body cells are different from one another, they are

Differentiation ▪ Though our many body cells are different from one another, they are all descended from a single cell ▪ The DNA in our cells contains all the instructions to build an organism, but different genes are active in different types of cells, –This determines the cell’s form and function (differentiation)

Cell Death ▪ Apoptosis: Programmed cell death ▪ Cells going through this apoptosis actually

Cell Death ▪ Apoptosis: Programmed cell death ▪ Cells going through this apoptosis actually shrink and shrivel in a controlled process

Henrietta’s Immortal Cells ▪ Finding human cells that grow in a laboratory took scientists

Henrietta’s Immortal Cells ▪ Finding human cells that grow in a laboratory took scientists nearly 30 years to find ▪ In 1951, an assistant prepared a cell line that divided vigorously –These cells were named He. La cells, after Henrietta Lacks, the patient from whom the cells were taken ▪ Although Henrietta passed away from cervical cancer, her cells live on and are still used today in laboratories all over the world to study cancer and numerous other cellular processes –He. La cells contributed to the work of Nobel Prize winners