Exam #4: Structure & Organization of Nucleic Acids Flashcards
What is non-coding DNA?
Non-protein coding sequences
List four types of non-coding DNA
1) Spacer Sequences
2) Introns
3) Genes encoding nonprotein-coding RNA
4) Repetitious DNA (most abundant)
Exon
Sequence of DNA translated into protein
Intron
Sequences of DNA that are spliced out
Gene Family
Genes that have a similar nucleotide sequence & encode similar proteins
Pseudogenes
Mutation of a gene gives rise to an inactive duplicate
How do gene families arise?
Spontaneous mutation and meiotic accidents
What is chromatin?
Complex of DNA and protein
How many chromosomes are found in a diploid human cell?
46: 2 sex chromosomes & 44 autosomes
How is the mitochondrial genome different from the nuclear genome?
- Circular molecule
- Present in multiple copies per organelle
- encodes 13 proteins & 24 RNA molecules
- Not extensively associated with proteins
Heterochromatin
- Stained
- Complex with proteins
- Transcriptionally inactive
- Periphery
Euchromatin
- Translucent
- Transcriptionally active
- Decondensed
What processes occur in the nucleolus?
Assembly of ribosomal subunits
Key features of the nuclear pore complex
- Nuclear basket on the nuclear side
- Protein ring anchored to the double membrane
- Central transporter inside protein ring
- Filaments on cytoplasmic side
Ran-dependent import into the nucleus
Ran & Importin = Protein & Ribosomal subunits into the nucleus
1) Importin + Cargo enters nucleus
2) Importin/Cargo + Ran-GTP= Cargo released
3) Ran-GTP/Importin= Exported to Cytoplasm
4) GTP hydrolyzed= Ran-GDP + Importin dissociate
5) Ran-GDP re-enters nucleus
Ran-dependent export from the nucleus
Ran & Exportin = protein out of the nucleus
1) Cargo + Exportin
2) Cargo/Exportin + Ran-GTP= Exported
3) GTP hydrolyzed= Dissociation in cytoplasm
4) Ran-GDP & Exportin re-enter nucleus
Semi-conservative Replication
- Each strand of parental DNA serves as a template for synthesis of a new complimentary DNA strand
- Each daughter DNA contains 1 parental strand and 1 newly synthesized strand
Replication Origin
Where replication begins; multiple origins on each chromosome
Bidirectional Replication
Replication is bidirectional from each origin
What are the nucleotide donors for DNA synthesis?
dATP, dGTP, dCTP, and dTTP
What is the significance of the pyrophosphate formed during chain elongation?
- Pyrophosphate is released as each nucleotide is incorporated into DNA
- Hydrolysis of pyrophosphate drives the reaction to the right
Key features shared by DNA polymerase
Note, y-DNA polymerase synthesizes mitochondrial DNA
1) Template-directed
2) Primer is required
3) Synthesize 5’–>3’
4) Newly synthesized DNA is anti-parallel to template
DNA Helicase
Use ATP-energy to unwind DNA double helix for replication
Single stranded DNA binding proteins
bind unwound DNA to prevent re-association
Topoisomerase
Relieve the supercoiling created by undwinding by nicking and religating DNA
RNA primer
Required for DNA synthesis; synthesized by DNA polymerase alpha
Leading Strand
Primer points toward the replication fork and synthesizes continuously
Lagging Strand
Primer points away from the replication fork and is synthesized in fragments
Okazaki Fragment
Fragments of DNA synthesized on lagging strand
Telomeres
End of chromosome with special TTAGGG sequence repeats
How are telomeres replicated?
Enzyme Telomerase that contains RNA molecule complimentary to telomere that acts as a template for extension of the 3’ end of DNA
Satellite DNA
Simple-sequence DNA i.e. identical repeats of short DNA sequences confined to the centromere & telomere
Example of a gene family
B-globin has 5 genes clustered together on chromosome 11: 2x adult globins, 2x fetal globins, and 1x embryonic globin
3 Levels of DNA Condensation
1) DNA wrapped around histones to form nucleosome
2) Nucleosomes associated to form 30nm solenoid fiber
3) 30nm solenoid fibers form 300nm loop domains
What organelle separates transcription and translation?
Nucleus
What does the separation of transcription from translation allow?
Post-transcriptional modification of RNA
mRNA Export from Nucleus
Ran-Independent
ORC
Origin of Replication Complex: protein that marks origin of replication
Primase
DNA Polymerase alpha
DNA Ligase
joins Okazaki fragments
DNA polymerase gamma
Elongates DNA
Topoisomerase Inhibitors
- Topoisomerase: Relieves supercoiling during replcation
- Drugs can inhibit this process and work as anti-cancer drugs or antibiotics
Doxorubicin
Human Topoisomerase inhibitor used in cancer chemotherapy
Nalidixic Acid & Ciprofloxacin
Bacterial topoisomerase inhibitors that work as anti-biotics
