Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
38 Cards in this Set
- Front
- Back
|
Genome |
- entire genetic complement of a cell or virus - in eukaryotes: one complete set of nuclear chromosomes (mitochondrial) - plants also have a chloroplast genome |
|
|
Genetic material in eukaryotes is what shape? |
- linear |
|
|
Genetic material in prokaryotes is what shape? |
- circular |
|
|
Genetic material in viruses is what shape? |
- double or single stranded - circular or linear - DNA or RNA but both |
|
|
In what order does genome size increase? |
- with evolutionary complexity Viral<Prokaryotic<Unicellular eukaryotic<Multicellular eukaryotic |
|
|
Topoisomerases |
- enzymes that create or alleviate supercoils |
|
|
Type I topoisomerases |
- usually monomeric proteins - induce transient single stranded breaks in the double helix - change supercoils one at a time |
|
|
Type II topoisomerases |
- usually multimeric proteins - induce transient double stranded breaks in the double helix - change supercoils two at a time |
|
|
How are supercoils eliminated? |
- a nick in the DNA |
|
|
E. coli chromosomes |
- about 4.5x10^6 bp packed into 2by1 micro - DNA is around 700 times the length of the cell` |
|
|
Where is are bacterial chromosomes found? |
- in the nucleoid in direct contact with cytoplasm (a region that is not membrane bound) |
|
|
What is the first way to promote compaction? |
- loop domains compact about 10 fold - loops connected to a central point attached to the cell membrane - loops are highly independent of each other |
|
|
DNA condensing (binding) proteins |
- positively charged - referred to as histone like |
|
|
What is the second way to promote compaction? |
- supercoiling |
|
|
C-value paradox (also give values for arthropods, fish, and angiosperms) |
- refers to multicellular eukaryotes - genome size does not correlate with organism size - arthropods: 250 fold - fish: 350 fold - angiosperms: 1000 fold |
|
|
What is the number of genes in humans? |
- 20 to 25 thousand - theoretical: 1 million |
|
|
What 3 types of DNA sequences are needed for chromosome replication and segregation? |
1. origins of replication 2. centromeres 3. telomeres |
|
|
How many genes does a single eukaryotic chromosome have? |
several thousand |
|
|
Intron number and gene size increase with what? |
higher eukaryotes |
|
|
Euchromatin |
- stains lightly - DNA is relatively extended and open - contains majority of genes replicated earlier in S phase |
|
|
Heterochromatin |
- stains darkly - DNA is tight and inaccessible - replicates later during S phase - contains relatively few genes - found close to centromeres and telomeres - in some species, comprise an entire chromosome |
|
|
Constitutive heterochromatin |
- regions that are always heterochromatic - permanently inactive in transcription - usually highly repetitive sequences |
|
|
Facultative heterochromin |
- regions that can interconvert between eu and hetero ex: barr body formation |
|
|
What is the size of the human genome? |
- 3x10^9 bp
- 2x10^13 m of DNA - can stretch to the sun and back more than 50 times |
|
|
Nucleosome |
- composed of histones and DNA |
|
|
Histones |
- 5 proteins: H1, H2A, H2B, H3, and H4 - small - basic - ubiquitous - evolutionarily conserved |
|
|
Beads on a string model |
- two molecules of each H2A, H2B, H3 and H4 - 146 bp of DNA wrapped 1.65 times around octamer - H1 monomer - linker DNA links beads together (varies in length) |
|
|
30nm fiber and two models |
- shortens total length of DNA another 7 fold 1. solenoid model 2. zigzag model |
|
|
Two parts of the nuclear matrix |
1. nuclear lamina: fibers that line the inner nuclear membrane 2. internal matrix proteins: connect to lamina and fill interior of nucleus (role remains controversial) |
|
|
Importance of radial loops attached to nuclear matrix |
1. compaction 2. organization of chromosomes within nucleus - each chromosome is located in a non overlapping territory during interphase |
|
|
Order of compaction of chromosomes |
1. DNA double helix 2 nm 2. nucleosomes (beads on a string) 11nm 3. zigzag structure 30 nm 4. radial loop domains 300 nm 5. further compaction of radial loops 700 nm 6. metaphase chromosome 1,4000 nm |
|
|
Metaphase chromosomes |
- end of prophase: sister chromatids entirely heterochromatic - highly condensed metaphase: undergo little transcription - radial loops are highly compacted and are anchored to a scaffold formed from nuclear matrix - histones needed for compaction of loops |
|
|
What does salt content do to histones? |
- high salt content: removes them - low salt content: leaves them |
|
|
Condensin |
- helps condense chromosomes - in cytoplasm during interphase - travels to nucleus at the start of metaphase - binds to chromosomes and compacts radial loops - number of loops does not change, they just become smaller |
|
|
Cohesin |
- helps in sister chromatid alignment - at end of S phase and beginning of prophase, sister arms are cohered - middle of prophase cohesin only remains at centromere - at anaphase, cohesin is degraded and sisters separate |
|
|
Structural Maintenance of Chromosome (SMC) proteins |
- found in condensin and cohesin - use ATP to catalyze changes in chromosome structure - 50 nm long |
|
|
Three reasons for telomeres |
1. prevent ends from being "sticky" 2. prevents ends from being degraded 3. allow proper replication |
|
|
Characteristics of telomeres |
- contain short, repeated sequences - mammals, birds & reptiles = 5’-TTAGGG-3’ - arabidopsis thaliana = 5’-TTTAGGG-3’ - tetrahymena thermophila = 5’-TTGGGG-3’ |
