A&P-Chapter 3 - Cell Cycle

Chapter 3 - Part 2 - Cell Cycle

Interphase Stages
- G₁(gap 1) - metabolic activity and vigorous growth
- G₀ - cells that cease dividing
- S (synthetic) - DNA replication
- G₂(gap 2) =preparation for division
Mitotic phase
- Mitosis
- Cytokinesis
Interphase - G₀
- G₀ represents not simply the absence of signals for mitosis but an active repression of the genes needed for mitosis.
- Cancer cells cannot enter G₀ and are destined to repeat the cell cycle indefinitely
- Most cells will leave the cell cycle, temporarily. They remain in G₁ until properly stimulated to begin dividing again.
- Often G₀ cells are terminally differentiated: they will never reenter the cell cycle but remain in G₁ until they die. (muscle and nerve cells)
Interphase - S phase (DNA replication)
- ____________ untwists the double helix and exposes complementary strands
- Each nucleotide strand serves as a template for building a new ________________ strand
- ___________________ covalently adds complementary ____________ to the template
- Since DNA polymerase only works in one direction:
  - A continuous _________ strand is synthesized
  - A discontinuous __________ strand is synthesized

Essential for body growth and tissue repair
The phases of mitosis are:
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis - division of the cytoplasm
  - Cleavage furrow formed in late anaphase by contractile ring
  - Cytoplasm is pinched into two parts after mitosis ends
Early and Late Prophase
- Asters are seen as chromatin condenses into chromosomes
- Nucleoli disappear
- Centriole pairs separate and the mitotic spindle is formed
Metaphase
- Chromosomes cluster at the middle of the cell with their centromeres aligned at the exact center, or equator, of the cell
- This arrangement of chromosomes along a plane midway between the poles is called the metaphase plate
Anaphase
- Centromeres of the chromosomes split
- Motor proteins in kinetochores pull chromosomes toward poles
Telophase and Cytokinesis
- New sets of chromosomes extend into chromatin
- New nuclear membrane is formed from the rough ER
- Nucleoli reappear
- Generally cytokinesis completes cell division

Surface-to-volume ratio of cells
Chemical signals such as growth factors and hormones
Contact inhibition
Cyclins and cyclin-dependent kinases (Cdks) complexes
Cell distruction - death
- Necrosis "cell homicide" -Inflammation with secondary injury to surrounding normal tissues.
- Apoptosis "cell suicide". -No Inflammation or secondary tissue injury.
Most cells divide an average of about 50 times
- mitotic clock - tips of chromosomes (telomeres about 15,000 base pairs)
- 25 - 200 base pairs are lost with each division
- When repeats are gone cell quits dividing.
Cell Differentiation-when cells develop different structures and specialized functions.
- Stem cell can divide to form a progenitor cell
  - totipotent -can give rise to any cell type
  - pluripotent - can give to almost any cell type in the body
  - multipotent - can differentiate into a limited range of cells
Cancer
- Division to frequent-->neoplasm-->tumor
  - benign -->lump in place
  - malignant -->lump extends into surrounding tissue resembling a crab --> metastasis
- Genes that cause cancer
  - Oncogenes activate other genes that increase cell division.
  - Tumor suppressor gene - normally regulate mitosis; if inactivated they will not regulate mitosis
  - Environmental causes?
- Cancer treatments are directed at procedures that kill ___________ cells. What normal cells do they also effect?

DNA serves as master blueprint for protein synthesis
Genes are segments of DNA carrying instructions for a polypeptide chain
Triplets of nucleotide bases form the genetic library
Each triplet specifies coding for an amino acid
Transcription
- Transfer of information from the sense strand of DNA to RNA
- Transcription factor
  - Loosens histones from DNA in the area to be transcribed
  - Binds to promoter, a DNA sequence specifying the start site of RNA synthesis
  - Mediates the binding of RNA polymerase to promoter
- DNA triplets are transcribed into mRNA codons by RNA polymerase
Translation to Polypetide - Roles of the Three Types of RNA
- Form Initiation complex
- Messenger RNA (mRNA) carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm
- Transfer RNAs (tRNAs) bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis
- Ribosomal RNA (rRNA) is a structural component of ribosomes

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