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BIO 201: LECTURE 30-35
Euchromatin
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High level of active genes; light-colored
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Heterochromatin
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Inactive, tightly coiled, dense, dark
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Constitutive Heterochromatin
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Permanently silenced DNA composed of highly repetetive sequences [telomeric & centromeric heterochromatin]
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Facultative Heterochromatin
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Inactivated only during certain phases of cell development, but can be converted to euchromatin. GENE EXPRESSION CAN BE CONTROLLED BY CONVERSIONS FROM EUCHROMATIN TO FACULTATIVE AND VICE VERSA
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Formation of Heterochromatin
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RNA recruits enzyme HMTase which catalyzes the addiction of methyl groups to H3 core histones on chromatin that is in the euchromatic state. The H3 core histones serve as binding sites for Hp1protein. Once HP1 is bound to histone tails, chromatin can be packed into higher order heterochromatin.
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The Nucleosome
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Lowest level of chromosome organization.
Histone H1 is an octomer protein which DNA wraps around.
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Centromere
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Middle of chromosome where two identical chromatids are attached. Involved in cell division as a point of mitotic spindle.
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Telomere
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Region of repetitive DNA at end of chromosome involved in protection.
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mRNA
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intermediate btwn gene and protein. Has same info as gene.
+ribosome=polysome. Where proteins are made!
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What is the function of the linker histone H1?
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Binds to DNA and brings nucleosomes together to create bead on a string structure. Seals off nucleosome at the location at which the linker DNA enters and leaves.
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4 Main Parts of Transcription
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1. Pre-Initiation- Assembles at specific sequences at the promoter site [w/ TATA box] at 5'. Includes initiation factors, RNA polymerase II and other TFs
2. Initiation- Transcription initiated by pol II
3. Elongation- Activated after phosphorylation of serine 5 on C-terminal addition of elongation factors
4. Termination- Newly synthesized pre-mRNA is released from DNA template
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pre-mRNA processing
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- Addition of 5' cap [prevents degradation]
- Addition of 3' poly(A)tail [stability]
- Removal of introns via Alternate Splicing [change order in which exons are spliced=different proteins]
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Svedburg
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Unit of sedimentation for ribosomal subunits-measure rRNA and it is non-additive
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Nucleolus
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In the nucleus for rRNA transcription & packaging into preribosomal subunits. Where ribosomes are made.
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Fibrillar Centers (fc)
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rDNA [for ribosomal RNA]
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Dense Fibrillar Component (dfc)
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Transcription of rRNA
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Granular Component (gc)
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Processing of pre-rRNP (protein + RNA). Mature ribosomal subunits are released for transport in the cytoplasm
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Ribosome Active Sites
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A: acceptor sites (large part where codon is bound)
P: peptidyl sites (small part where initiator tRNA binds)
E: exit site (last stop before tRNA is released)
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tRNA |
carries appropriate amino acids to ribosomes via Aminoacyl synthetase enzymes.
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Anticodon
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group of three bases on a tRNA molecule that are complementary to an mRNA codon [group of 3 bases]
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Translation Phases
1) Initiation
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1. Initiation-starts at AUG codon on mRNA binds to one subunit of the ribosome, a tRNA with the amino acid methiamine [MET] attached docks in the ribsome's P site
Requires 1 GTP
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Translational Phases
2) Elongation
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2. Elongation- elongates the poloypeptide by 1 amino acid per cycle. Requires 2 GTP [3 all together!]
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Translational Phases
3) Termination
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3. Termination- brings a stop codon into the position associated with the empty A site; the release factor binds and then frees the polypepetide and dissociates the ribosome. Stop Codon will begin with U
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Prokaryotic IF 1 [Initiation Factor Enzyme]
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Promotes mRNA and Small Subunit binding
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Prokaryotic IF 2 + GTP
[Initiation Factor Enzyme]
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Attaches aa-tRNA to P site
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Prokaryotic IF 3 [Initiation Factor Enzyme]
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Blocks premature binding of Large and Small Subunits
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Elongation Factor Tu+GTP [Elongation Factor Enzyme]
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Binds new aminoacyl-tRNA to A site
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Peptidyl Transferase (passive) [Elongation Factor Enzyme]
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Transfers peptide from P site tRNA to A site tRNA
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Elongation Factor G + GTP
[Elongation Factor Enzyme]
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Powers translocation of ribosome down mRNA, 3 nucleotides
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Levels of the regulation of Gene Expression
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1) Transcriptional (Nucleus)-Gene copied to mRNA
2) Processing (Nucleus)- mRNA modified to final strand
3) Translational (Cytoplasm)-Location of mRNA, stability, protein factors bound
4) Post-Translational (Cytoplasm)- Protein stability
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Meselson & Stahl Experiment
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Bacterial cells grown in heavy N, then light N. They replicate semi-conservatively= each of the two double stranded DNA helices consisted of one strand coming from the original helix and one newly synthesized. N became diluted towards end.
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DNA Polyermase
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Enzyme that creates the new strand of DNA. ONLY 5'->3'
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DNA Helicase
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Unwinds DNA at replication fork into single strands using ATP>ADP +Pi
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SSB (Single-stranded DNA Binding Protein)
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Keeps DNA single stranded
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RNA Primase
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Initiates DNA replication on both strands by adding RNA primers. 1 on leading strand and 1 for each okazaki fragment.
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DNA Polymerase
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Synthesizes new DNA strand on each template strand
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RNase H
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removes RNA primers which is then filled with DNA nucleotides
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DNA Ligase
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Seals okazaki fragments on lagging strand into continuous DNA strand
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