EXAM 1 - Population, DNA Replication, Mitosis Meiosis Flashcards
DNA Structure
Nitrogenous base
pentose
sugar
phosphate
double helix 5’-3’ antiparallel structure
Nucleosome Structure
Two coils of DNA on Histone core
~ 200 base pairs of DNA
Octomere on each of H2A, H2B, H3, H4
H1 - space between nucleosome
Chromatin Structure Hierarchies
- Primar struc. - 2 coils of DNA on nucleosomes core
- Secondary struc. - helical array of nucleosomes
- Tertiary - Packing of nucleosome arrays into chromatin
visible chromosomes are transcriptionally inert - so raveled up can’t unravel and make gene copies
Types of Chromatin:
*Heterochromatin: densely packed, not transcribed (some nonsense, some repressed)
- Constitutive: repeated sequences, genes not
expressed
- Facultative: the form of an entire chromosome that
is expressed
- ex> — x chromosome barr body: color blind
(can’t see red or yellow well), hemophilia (unable
to clot blood)
*Euchromatin: active genes, transcribed as needed
- found on nucleosomes core and area between
Cell Cycle - study on a white board
Barr Body
small, densely staining structure in the cell nuclei of female mammals - condensed in X chromosome
ex. color blind, hemphilia
Cyclin
Cyclins activate Mitotic cdks (cyclin dependent protein kinases)
Role of Cyclins
Cyclins activate Mitotic cdks (cyclin dependent protein kinases)
Protein kinases phosphorylate proteins (enzymes) to catalyze cell reactions
When cyclins are added, cells move through cell cycle checkpoints
Role of Cyclins
Cyclins activate Mitotic cdks (cyclin dependent protein kinases)
Protein kinases phosphorylate proteins (enzymes) to catalyze cell reactions
When cyclins are added, cells move through cell cycle checkpoints - found at 3 major checkpoints (G1, G2, M Phase)
3 cell populations in the body:
Go (nondividing): muscle and nerves
Cells that barely divide but can when stimulated: Liver (G2)
Cells that rapidly divide:
- Skin, hair
- GI epithelium
- Bone marrow, blood
- Reproductive cells
Role of p53
p = protein
53 = 53 kilodaltons
- Regulates cell division, wild type form halts cell divisions, arrests cells in G1
- mutant forms cause abnormal cell division
- half of all cancers involve mutation of this gene
- gene can trigger “apoptosis” – programmed cell death
- some carcinogens are found to alter p53
Factors that stimulate cell cycle
- Oncogenic factors
- Bcl 1 and 2 genes (B cell lymphoma)
- BRCA 1 and 2: linked to 80% chance of breast, ovarian cancer
- Ras gene
- Cyclin proteins (may be triggered by bcl gene)
Factors that inhibit cell cycle
- P53 gene
- bax genes
- ICE (interleukin converting enzyme)
- Ubiquitin
- these same factors can also trigger apotosis
Factors that inhibit cell cycle
- P53 gene
- bax genes
- ICE (interleukin converting enzyme)
- Ubiquitin
- these same factors can also trigger apoptosis
Initiation of DNA replication
Initiator Proteins: unwind DNA double helix
Helicase: continues winding
Topoisomerase: swivel prevents tangling of DNA supercoils
DNA replication
DNA polymerase directs DNA replication
DNA replicates in a 5’ to 3’ direction
Begins w/ attachment of RNA primer
followed by DNA polymerase
Where possible, RNA primer replaced via exonuclease/ ligase
DNA Replication Enzymes
Initiator Protein
Helicase
Topoisomerase
Exonucleases
Endonucleases
RNA Primer
DNA Ligases
DNA Polymerase
Leading Strand
Lagging Strand
Initiation Protein
Unwind DNA - binds to origin of replication an initiate unwinding of DNA double helix - both cell types
Helicase
Unwinds dsDNA - both cells (eukary and prokary)
Topoisomerase
Sins the ends of the DNA so the stands won’t get knotted up
Exonucleases
an enzyme which removes successive nucleotides from the end of a polynucleotide molecule
Endonucleases
an enzyme which cleaves a polynucleotide chain by separating nucleotides other than the two end ones
DNA Polymerase
DNA synthesis
1. Leading Strand: s looking greek symb. - eu -
2. Lagging Strand - alpha - eu -
DNA Ligases
(both cell types) – makes covalent bonds to join together adjacent DNA strands, including the Okazaki fragments in lagging-strand DNA synthesis and the new and old DNA segments in excision repair of DNA
