ch.12 - mitosis.docx

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Biological Sciences
BIOSC 0150
Christine Dahlin- Universityof Pittsburgh Johnstown

1 General biology 1 Chapter 12 – Cell division: Mitosis Cell division – reproduction of cells - Pass genetic material to cellular offspring Prokaryotes – produce entire other organisms Eukaryotes – develop from a single cell Cell cycle terms - Genome – all the DNA (genetic info) in a cell o Packaged into chromosomes  Long DNA molecules coiled around protein  Each chromosome – hundreds to thousand genes  DNA + protein = chromatin - Diffuse chromatin – chromatin coils up after dividing - Sister chromatids – chromosome coiled up tight; dyads – duplicated chromosome How do we get new cells? - Mitosis & cytokinesis – creates somatic cells (nonreproductive cell) o Full set of chromosomes - Meiosis – creates gametes (reproductive cells) o Have only ½ of chromosomes per cell Specific differences - Eukaryotes have set numbers of chromosomes - Human somatic cells – 46 chromosomes - Human gametic (reproductive) cells – 23 chromosomes - Varies in species: chimpanzee (48), hedgehogs (90), cabbage plants (18) What can cells do? - “Hang out” and do their thing - Prepare to divide then divide (“cycling”) - Also die by apoptosis = suicide How does cell decide what to do? - Monitor environment – intra and extracellular - Cell asks – whether or not they are ready to divide? o Where are signals to divide? - Division occurs in response to a signal Ex/ growth factor o Binds to receptor in membrane o And enter cells so then cell commits to dividing - Interphase – G1 (or 1 gap phase) in response to a signal to divide o S (DNA synthesis) – cell prepares to divide o G – 2ell prepares to divide o Mitotic (M phase) – include mitosis and cytokinesis where cell finally divides - Mitosis – cell division o Have exact copies of DNA and split in half o Growth or repair/replacement 2 General biology 1 Chapter 12 – Cell division: Mitosis Overview - Preparation – cell decides to divide - Replicate the DNA – copy all chromosomes - Mitosis – segregate the chromosomes and move them to the daughter cells (new cells) - Cytokinesis – when a cell has physically splits apart into 2 daughter cells (and cytoplasm) Cell cycle 1. Interphase – prepare to divide o Make protein, organelles and replicate DNA o Division of mitosis and cytokinesis - Subphases of interphase are G1, S, G2 phase a. G (1 gap) – “resting”  Make decision to divide or not b. S (synthesis phase) – DNA replication c. G –2preparation for mitosis Orderly/regulated progression - G1 – grow and deciding whether or not to divide - S (synthesis) – DNA replication o Making exact copies of cell: duplicates - G2 – more growing of cell Chromosomes separate during mitosis - Monad (an unreplicated chromosome) get duplicate  occurs in G1 phase - Sister chromatids – monad duplicate into 2 identical joined chromosome o A duplicated chromosome that is condensed - Then sister chromatids get separate into 2 chromosomes that contain an original chromosome and a replicated chromosome pairs  occurs in M phase Centromere – a DNA sequence at the “constriction” of a chromosome When and why cell divide? - Cell control system – molecules that trigger and coordinate key events - Human skin cells: divide frequently - Live cells: divide as needed i.e – wound repair - Some specialized cells never divide once fully formed! Ex/ nerve cells Cell cycle transitions: - Controlled by Cdks and cyclins - Cycle-dependent kinase (Cdk) o Enzyme – phosphorylates (transfer phosphate group from ATP) o Activates or inactivates proteins o Cell cycle progress when Cdk is active Cdks – always present in cell but not always active - Only active when cyclins bind to - BUT cyclins NOT always present 3 General biology 1 Chapter 12 – Cell division: Mitosis - Levels “cycle” is high, low, high, low, … - Based on gene expression and degradation Cyclin – activating molecule (a protein) that fluctuate cell concentration from its cyclically - Activates CDK phosphorylate proteins - Increase during S and G2 phase - High cycle means cell ready to divide Ex – MDK: cyclin-CDK complex which requires high cyclin! When there is enough MDF (M phase promoting factor), mitosis begins Regulation of cell cycle at G2 complex by Cdk and cyclin - An active kinase include cyclin-Cdk complex - Several cyclin-Cdk protein complexes regulate all stages of cell cycle Cell cycle checkpoint - Stop cell cycle when there is a problem o Survey cell – monitor internal and external signal
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