CBG exam 2 flashcards ; pt2

Binary Fission

·      Occurs in prokaryotes – (doesn’t use mitosis)

1.     Origin replicates (single origin of replication)

2. Both origins of replication move to opposite ends of cell

3. Cell elongates and then divides

·      Taking place in the cytoplasm – doesn’t have a nucleus

Prokaryote vs. Eukaryote division

·      Most eukaryotes go through mitosis while prokaryotes go through binary fission.

·      Some unicellular eukaryotes have an intermediate division in which nucleus divides.

·      A = Binary vision = no nucleus

·      B = Microtubules go through the nucleus and pulls chromosomes apart

·      C = Micro form within the nucleus and pull apart

·      D = Mitosis

Cell Cycle

1.     Interphase

2.     Mitosis

3.     Cytokinesis

·      During S phase; every time you replicate you’re losing a small amount of DNA specifically in the daughter cells

Cell Senescence

·      Human cells cannot keep dividing because of shortening of telomeres (ends of chromosomes), this is called cell senescence.

o   Cell can no longer divide because you’re loosing proteins and DNA needed for cell maintenance

o   Loosing DNA at the end of a strand vvv

The Immortal Life of Henrietta Lacks

·      Henrietta Lacks (1920-1951)

·      Immortal HeLa Cell line

o   Can’t do research without her cell

Telomerase: the key to immortality

·      Telomere: ends of chromosomes have tandem repeats (such as GGGGTT). Telomeres shorten each time the cell divides

·      Loss of telomeres and shortening of chromosomes is thought to be an important reason why cells age and undergo senescence

·      Telomerase: an enzyme that restores telomeres. It is expressed in germ cells, stem cells, and cancer cells but not differentiated adult human cells

·      The telomerase gene has been cloned. Introduction into human fibroblasts prevents senescence and makes cells immortal.

Can telomerase be activated in human cells to prevent aging?

How does telomerase work?

Cell cycle checkpoints

Checkpoints: prevent the cell from entering the next phase of the cycle before the preceding phase has been completed

G1 checkpoint: monitors whether the environment is favorable for cell division (growth factors). It also monitors for DNA damage

G2 checkpoint: checks if DNA replication is complete. Also causes cell cycle arrest in response to DNA damage, allowing cells to repair any damaged DNA before division

M checkpoint: monitors whether chromosomes are intact and lined up properly

How are checkpoints regulated?

The cell cycle is controlled by cyclins and cyclin dependent kinases

·      Cyclins: a family of proteins that cycle in abundance during the cell cycle. Cyclin B accumulates during interphase but drops quickly in mitosis. Cyclins control the cell cycle in all eukaryotic cells

·      Cyclin dependent kinases (cdk): proteins that phosphorylate and cause cells to move to next cell cycle phase. They are always present but they require a cyclin to become an active kinase

Maturation promoting factor (MPF)

·      MPF: first purified complex of cyclin and cdk, promotes maturation of oocytes by completion of meiosis - also stimulates movement of cells from G2 into M phase

·      Cyclin B is the regulatory subunit and must be present for function of the Cdc2 (cdk1) kinase

·      Cdc2 (cdk1) phosphorylates nuclear lamins (breaks down nucleus) and proteins that condense chromosomes

MPF role in cell cycle

1.     Cyclin B synthesized in S and G2.

2.     Cyclin B binds CDK1 making MPF

3.     MPF phosphorylates proteins during M phase

4.     Cyclin B is degraded in anaphase.

Properties of Normal cells

·      Growth Factors - Normal cells within the body respond to growth factors (example: hormones or cytokines) to function within the cell cycle.

·      Density dependent inhibition - Crowded cells stop dividing.

·      Anchorage dependence - Cells need to be attached to a solid surface in order to divide.

Cancer cells leave normal cell cycle

·      Cancer is a malignant neoplasm (or tumor)

o   Neoplasm (neo = new, plasm = growth): a new growth of cells that is abnormal

o   Malignant = cancer: when cells invade adjacent tissue they are considered cancer

o   Benign = non-cancerous: tumor cells do not invade, but can kill if it’s not possible to remove tumor due to location (brain)

Why study cancer? Cancer is a disease of cells. Progress in understanding normal cell biology has come from studying cancer cells