Chapter 10 Flashcards
Bacteria divide by
binary fission. Asexual reproduction
Bacterial genome
Single, circular chromosome tightly packed in the cell at the nucleoid region. (Prokaryotes don’t have nuclei). New chromosomes are partitioned to opposite ends of the cell
Septum
Forms to divide cell into 2 cells
Protein FtsZ
ORI. Termination site
Origin of replication of chromosomes
Eukaryotes chromosomes
Linear chromosomes. Single or double armed
Human chromosomes
46 chromosomes in 23 nearly identical pairs
22 pairs
Autosomal (do nothing to determine sex)
XX=Female
XY= Male
Typical human chromosome
Composed of chromatin complex of DNA and protein
140 million nucleotide long.
Over 2 meters of DNA inside a diploid human nucleus
Heterochromatin
More condensed
Silenced or fewer genes (Methylated)
Gene poor (High AT content)
Stains darker
Euchromatin
Less condensed
Gene expressing
Gene rich (Higher GC content)
Stains lighter
Levels of Chromatin organization
1 Naked DNA
2 Nucleosome - first level of wrapping
3 Solenoid
4 Chromatin loops
5 Chromosomes
Nucleosome
Complex of DNA and histone proteins (ball like)
DNA duplex coiled around 8 histone proteins every 200 nucleotides
Histones are positively charged. DNA phosphate groups (in nucleotide) negatively charged
Solenoid
Nucleosomes wrapped into higher order coils
Leads to a fiber 30 nm diameter.
During mitosis chromatin in solenoid arranged around scaffold of protein to achieve maximum compaction
Karyotype
Particular array of chromosomes in an individual organism. (Seeing genome)
Diploid vs Haploid
Diploid (2n) 2 copies of all chromosomes, 1 from mom 1 from dad. Somatic cells- nothing to do with reproduction
Haploid (n) 1 set of chromosomes. Sperm or ovum. Sex or germ line cells
Homologous
Pairs of chromosomes
SRY region
Area that males turn on after the beginning and during the embryotic process
Before DNA replication
each chromosome composed of a single DNA molecule (single armed) (monad)
After DNA replication
each chromosome is composed of 2 identical DNA molecules, held together by cohesin proteins. One chromosome composed of 2 sister chromatids.
Kinetochores
Microtubules attach to move chromosomes
Human mitosis
Somatic cells. Growth, repair, regeneration. Start with one cell. One round of cell division. End with 2 identical new cells: Daughter cells.
Eukaryotic cell cycle two phases
M phase/cytokinesis: Eukaryotic nuclear division (mitosis) and cell division (cytokinesis)
Interphase (bigger part) - Cell is being a cell, nucleus is visible, cell metabolic functions, including DNA replication, occur. Begins after cytokinesis and ends when mitosis starts.
Interphase phases
G1 (Gap phase 1) - Growth of cell, longest phase. Primary growth phase
S (Synthesis) - Single to double arm. DNA replication create sister chromatids attached at centromere
G2 (Gap phase 2) - Some growth. Mostly preparation for M phase. Organelles replicate, microtubules organize, chromosomes coil more tightly
Resting phase G0
Cells often pause in G1 before DNA replication and enter a resting state. Spend more or less time here before resuming cell division. Most cells in animal body are in G0. Muscle and nerve cells remain there permanently. Liver cells can resume G1 phase in response to factors during injury.
Centromere
Point of constriction
Kinetochore
Attachment site for microtubules
Cohesin
Protein attachment for chromatids at centromere
M (Mitosis) Phase
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Prophase
Chromosomes condense and appear as two sister chromatids held together at the centromere. Nuclear envelope breaks down. Mitotic spindles (from centrioles) begin to form on opposite sides of cell. Asters-radial array of microtubules in animals (not plants. Golgi and ER are dispersed
Prometaphase
After disassembly of nuclear envelope, chromosomes attach to microtubules at kinetochores from opposite poles and begin to move to equator
Metaphase
Alignment of chromosomes along metaphase plate. Under tension from microtubules
Anaphase
Begins when centromeres split. Removal of cohesin proteins. Sister chromatids pulled towards opposite poles. No longer chromatids, now chromosomes
Telophase
Spindle apparatus disassembles, Nuclear Envelope forms. Chromosomes begin to uncoil and disperse. Nucleolus reappears. Golgi and ER reform
Cytokensis
Cleavage of cell into equal halves. Animal cells constriction of actin filaments produces a cleavage furrow. Plants form cell plate between nuclei
Control of cell cycle 2 concepts
1 Cycle has two irreversible points
A. Replication of genetic material (S-phase)
B. Separation of the sister chromatids (anaphase)
2. Cell can be put on hold at specific points called checkpoints. Process checked for accuracy, allows for response to internal and external signals
3 Checkpoints
- G1/S checkpoint - Decides whether or not to divide
- G2/M checkpoints - Makes a commitment to mitosis, assesses success of DNA replication, can stall the cycle if DNA has not been accurately replicated
- Late metaphase (Spindle Checkpoint) - Cell ensures that all chromosomes are attached to the spindles by microtubules.
Cyclin-dependent kinases
(Cdks) Enzyme kinases that phosphorylates proteins (attaches phosphate group). Primary mechanism of cell cycle control. Cdks partner with different cyclins at different points in the cell cycle. Cdk itself controlled by phosphorylation.
Cdk-cyclin complex
Also called Mitosis-promoting factor (MPF) promotes mitosis
Activity of Cdk controlled by pattern of phosphorylation. Cdk has active and inactive sites for cyclin to bind to
Anaphase-promoting complex (APC)
Cyclosome (APC/C)
Function is to trigger anaphase itself. Marks securin for destruction. Securin inhibits separase (destroys cohesin). No securin = no inhibition of separase, separase destroys cohesin and sister chromatids can separate. APC marks securin for destruction
Securin
Enzyme found in all cells. Secures cohesin and inhibits anaphase. Need to remove securin for anaphase to occur
Separase
Enzyme that destroys cohesin once securin is is removed
Cancer and two genes
Unrestrained, uncontrolled growth of cells. Failure of cell cycle control.
Tumor suppressor genes
Proto-oncogenes
Tumor-suppressor genes
Genes whose activity includes preventing tumor formation (unwanted cell growth/division). Both copies of a tumor-suppressor gene must lose function for the cancerous phenotype to develop.
p53: G1 checkpoint
p53
G1 checkpoint monitors integrity of DNA and prevents the development of mutated cells.
Abnormal p53 fails to stop cell division, damaged cells divide and cancer develops
Proto-oncogenes
Normal cellular genes that become oncogenes when mutated. oncogenes can cause cell to be cancerous. Only one copy of proto-oncogene needs to undergo mutation for uncontrolled division to take place. Some proto-oncogenes encode receptors for growth factors, if receptor is mutated on, cell no longer depends on growth factors.
