Exam Three Bio - Ch 12, 13, 14, 15

Mitosis - the only way to get new genetically identical cells

• somatic cells - normal body cells

meiosis - produces genetically different daughter cells galled gametes responsible for reproduction

chromosome - single long DNA strand wrapped around histones and containing genes

• one chromosome has many genes, which code for products

unreplicated chromosome → replicated chromosome → condensed replicated chromosome

• even when chromosomes copy, if they are attached to each other they are one chromosome; this is known as sister chromatids, which remain joined at the centromere until they are separated during cell division.

m-phase: mitosis or meiosis

interphase: gap 1, s-phase, gap 2

• these contain checkpoints to ensure cell properly divides

• chromosome NEVER changes during mitosis

prophase - chromosomes condense, spindles form

• spindles are made of microtubules and are able to move chromosomes and pull chromatids apart

• centrioles move to opposite ends of the cell

prometaphase

• nuclear envelope breaks so microtubules can attach to chromosomes at kinetochores

• kinetochores are structures on the centromere of sister chromatids

• they are proteins providing a site of connection

metaphase - central alignment of chromosomes

• spindle fibers move chromosomes to metaphase plate and are anchored to cell membrane

anaphase

• microtubules shorten and pull sister chromatids apart, ensuring each daughter cell receives the same number of chromosomes

• because sister chromosomes are not attached, they are now called chromosomes

telophase

• reformes nuclear envelope and chromosomes recondense in each daughter cell

• each daughter cell now has unreplicated chromosomes

cytokinesis - splitting of cytoplasm

• plants build a new cell wall with their cell plates

• animals just split membrane in half

  • this process happens with actin and myosin proteins, creating cleavage furrows

prokaryotic division - binary fission

• prokaryotes do not have nuclei or spindle fibers

• replicate circular chromosomes and undergo the same process

chromosomes

• homologs - chromosomes of same size and shape with same genes in same place

• sister chromatids - identical PART of a chromosome

• non-sister chromatid - one chromatid is on one homolog and a separate chromatid is on a different homolog

meiosis - goal of halving chromosomes and producing gametes

• increases genetic diversity

• chromosome number is restored during fertilization

• all organisms have a specific number of chromosomes unique to them

• x and y are sex chromosomes

• chromosome pairs that do not determine sex are called autosomes

• homologous chromosomes: NOT identical

• bivalence: paired, replicated homologs attached during prophase I

ploidy

• number of chromosome pairs

• n is the number of unique chromosomes in a cell

• haploid: meaning single form, denoted by n, one distinct type of chromosome

• diploid: meaning double, denoted by 2n, one paternal and one maternal chromosome

• polyploidy: 3 or more of each unique chromosome

• ploidy changes throughout an organisms life cycle

  haploid gametes combine to form diploid zygotes

• then diploid zygotes undergo mitosis and develop into diploid adults

priori to meiosis

• chromosomes always replicate in s-phase

• checkpoints remain the same and now pairing matters

two complete cell divisions

• meiosis 1: homologous chromosomes separate

• meiosis 2: sister chromatids separate

meiosis 1 - promoting genetic variation via crossing over, creating new allele combinations

• prophase 1 - undergoes synapsis, create chiasmata, and complete crossing ober

  • homologs come close together and become bivalent during synapsis

  • chiasmata - non-sister chromatids join and prepare to cross over

  • crossing over - non-sister chromatids exchange genetic information at genes / alleles

• metaphase 1 - homologs line up at the metaphase plate

• anaphase 1 - homologous pairs separate into individual replicated chromosomes

  • crossing over - genetic recombination

  • independent assortment - the way homologs align at metaphase plate

  • fertilization - union of two random gametes

    • outcrossing and self pollination

Nondisjunction - either homologs or sister chromatids fail to separate

• aneuploidy - cells have an abnormal amount of chromosomes

• if nondisjunction occurs in meiosis 1, two n+1 cells and two n-1 cells are produced

• karyotype: visualization of all chromosomes to find aneuploidy

  • trisomy-21: three chromosomes are at chromosome 21, cause of down syndrome

cell cycle regulation

• checkpoints cause cell to stay in that phase until it’s ready for division

• g1: is the cell large enough, does it have enough nutrients, are social signals present and is the DNA undamaged?

  • g0: mature / unfixable cells never pass through this checkpoint

• g2: have the chromosomes been successfully replicated and is the DNA undamaged?

• m-phase

  • checkpoint between prometaphase and metaphase ensuring spindle fibers properly attached and the chromosomes properly separate

proteins

• cyclins: only produced when needed in a specific part of the phase

  • at G1, G1 to S phase, S phase and M phase

  • work with cyclin-dependent kinases (cdks)

  • only work when paired with cyclin

  • activate protein by removing phosphate from ATP and donate to a specific protein

• MPF: m-phase promoting factor

  • cyclin and cdk pair in the cytoplasm telling the cell it’s ready for mitosis

  • cyclin is produced in g1 and peaks during m-phase

    • binds to cdk and activates it, cycling concentration goes down until the cell is ready for another cycle

regulation of MPFs

• interphase

  • cyclin concentration increases and attaches to cdks

  • cdk has an extra phosphate attached, preventing it from activating the cycle

• G2

  • phosphate group is removed and activates cdk

• m phase

  • cyclin degrades and cdk becomes inactive once division begins

G1 checkpoint

• controlled by growth factors

  • hormones promoting the cycle like gas

• tumor suppressors

  • restrict cell division like brakes

  • p53: DNA repair

  • Rb: prevents G1 from transitioning to S-phase

• E2F - activates s-phase

  • must be held back until cell is ready

  • growth factor produced cyclin and E2F

  • Rb inhibits e2F

  • cyclin binds to cdk, which is inhibited by phosphate

  • phosphate is removed from cdk by an enzyme, cdk removes phosphate from ATP and attaches it to the Rb and inactivating it

  • once rb is inactive, E2F is released and kicks off the cycle

Cancer

• caused by too many growth factors, too much phosphate enzyme, too much e2f

• also by too much cyclin or mutated Rb

• cancer is many diseases caused by uncontrolled cell division

  • invades nearby tissue and metastasizes

• tumor - mass of uncontrolled cells

  • benign: noncancerous and noninvasive mass

  • malignant: metastasizing cells

  • driver genes

    • protooncogenes - promote cell growth and division by coding for growth factors

    • oncogenes - mutated alleles causing uncontrolled division

    • too many of either of these cause cancer

• tumor suppressors also can mutate or be broken, causing cancer

Growth Factors

• tell the cell to create e2f and cyclin

• RAS - gene involved in many cancers

  • part of signal transduction pathway that tells cell to produce e2f

  • when mutated, RAS never inactivates and/or tells cell to activate without growth factor

• p53 - cell cycle control and DNA repair

  • transcription factor

  • DNA damage sets off signaling pathway, p53 tells nucleus to stop cycle until the dna is repaired

  • defective or missing p53 leads to uncontrolled division

Genetics

• one gene mutation usually isnt enough to cause cancer

  • one oncogene and many tumor suppressor defects must be present

• genetic predisposition: increased likelihood of developing a specific cancer

  • individuals inherit one broken copy and only need to have one more mutation to develop cancer

• BRCA: two copies of every gene, individual inherits one of them, it only takes one more mutation to get cancer

environmental factors

• carcinogens - substances proven to cause cancer

  • tobacco, alcohol, UV, pollution

• cancer is treated with surgery, chemo, radiation, targeted therapy and immunotherapy