How Cells Reproduce Chapter 8

What is the purpose of reproduction? Grow in size Repair old and worn out cells Replace Reproduce

New cell has to be… An exact copy of the parent cell i.e. the nuclear material identical to parent Why? The chromosomes in nucleus is the control center of the cell So the chromosome numbers and types of daughter cell HAS to be identical to parent.

Cell Cycle Process of events which a cell is born, carries out its activities and reproduces to make a cell identical to it. Cycle starts when a new cell forms During cycle, cell increases in mass and duplicates its chromosomes Cycle ends when this cell divides

So what is a chromosome? Chromosome A B A double stranded linear DNA molecule associated with proteins. In a non-dividing cell, it would look like diagram A and is called chromatin In a cell getting ready to divide, it will look an X and is called a chromosome Chromosome

Chromosmes vs chromatin Chromosomes Tightly packed DNA Found only during cell division DNA not being used to make proteins Chromatin Unwound DNA Found during Interphase DNA being used to synthesize proteins and/or replicating

Stages of Cell Cycle

Cell Cycle Two main phases Interphase Cell division G1 (growth/generation/gap) S (synthesis of DNA) G2 Cell division Mitosis Cytokinesis

Interphase Longest part of the cycle Cell increases in mass Number of cytoplasmic components increases Cell develop carry out functions DNA is duplicated

Generation/Growth 1 Phase right after cell division Cell grows in size Organelles are made if necessary Cell carries out its functions Example? ________________ At the end of G1, the cell makes a decision “To divide or not to divide”

Growth 0 Cells will not divide Will carry out the functions it was meant to perform Why is that important? ______________

Synthesis (S) Cell has made a decision to divide The chromosomes/DNA will now make exact copies of each other Amount of DNA doubles by the end of this phase

Generation/Growth 2 Cell gets ready for cell division Makes organelles and proteins necessary for cell division Spindle fibers Centrioles

Prokaryotic organisms Division Mechanisms Eukaryotic organisms Mitosis Meiosis Prokaryotic organisms Prokaryotic fission

Cell division Mitosis separates the replicated chromosomes into two equal groups Cytokinesis builds the cell membrane between the two nucleii The Rutgers Lessons

Cell Division Period of nuclear division - mitosis Usually followed by cytoplasmic division Four stages: Prophase Metaphase Anaphase Telophase

Prophase Duplicated chromosomes begin to condense New microtubules are assembled One centriole pair is moved toward opposite pole of spindle Nuclear envelope starts to break up

Metaphase Spindle forms Spindle microtubules become attached to the two sister chromatids of each chromosome All chromosomes are lined up at the spindle equator Chromosomes are condensed

Anaphase Sister chromatids of each chromosome are pulled apart Once separated, each chromatid is a chromosome

Telophase Chromosomes decondense Two nuclear membranes form, one around each set of unduplicated chromosomes

Results of Mitosis Two daughter nuclei Each with same chromosome number as parent cell Chromosomes in unduplicated form

Cytoplasmic Division Usually occurs between late anaphase and end of telophase Two mechanisms Cleavage (animals) Cell plate formation (plants)

Animal Cell Division Cleavage furrow

Plant cell Division Cell Plate Formation

When Control Is Lost Growth and reproduction depend on controls over cell division Checkpoint proteins: Growth factors invite transcription of genes that help the body grow Other proteins inhibit cell cycle changes, such as after chromosomal DNA gets damaged When all checkpoint mechanisms for a particular process fail, a cell loses control over its replication cycle An example of this is cancer

Types of Cancers Are abnormal masses of cells that lost controls over how they grow and divide Benign – grow slowly and retain surface recognition proteins that keep them in a home tissue (noncancerous) Malignant – grow and divide abnormally, disrupting surrounding tissues physically and metabolically (cancerous)

Cancer Research Described in Egyptian records 2625 BC In Greek records ~440 BC Greek for “Like a crayfish/crab”