Quiz 3 Flashcards
Genome
entirety of information contained within an organism’s gene
Base pairing rules
Adenine (purine) pairs with thymine (pyrimidine) with two hydrogen bonds
Guanine (purine) pairs with cytosine (pyrimidine) with three hydrogen bonds
Gene
Basic unit of heredity
Introns
non-coding regions of a gene
Exons
Coding regions of a gene
During RNA processing, ______ are removed, and ______ form mature RNA.
Introns, exons
Describe regulatory sequences
Do not encode for a protein
Help regulate gene expression
What are four examples of regulatory sequences?
Promotors, terminators, enhances, silencers
Describe a promotor.
Located upstream
Where RNA polymerase binds and initiates transcription
Describe a terminator.
Located at 3’ end
Acts as a stop signal for RNA polymerase
Describe enhancers: where are they located, what binds to them, and what is their function?
Located upstream or downstream
Bound by activators
Up regulate gene transcription
Describe silencers: what binds to them and what is their function?
Bound by repressors
Down regulate gene transcription
What does the solenoid model propose?
Nucleosomes are arranged in a left helical confirmation with 6 or more nucleosomes per turn. This shortens DNA length by 50-fold.
Chromatin exists in two forms:
- Euchromatin
- Heterochromatin
Describe euchromatin during interphase.
dispersed in nucleus and replicated throughout S phase
What are characteristics of euchromatin?
- Gene-rich
- Less compact
- Actively transcribed region of chromatin
The histone tail amino acids of euchromatin are __________.
Acetylated
Why are the histone tail amino acids in euchromatin acetylated?
Acetylation increases negative charge on histone proteins
—> Reduces histone-DNA affinity
—> Reduces chromatin compaction
—> Allows easier access to DNA
Nucleosome contains a protein core made up of four histone core proteins:
- H2A
- H2B
- H3
- H4
All histone core proteins have variants with the exception of which histone core protein?
H4
List the variants of each histone core protein.
- H2A — H2AX, H2AZ
- H2B — TH2B, TSH2B
- H3 — H3.1, H3.2
- H4 — no variants
Describe amino-terminal tails.
Unstructured and highly mobile
Comprised of about 30 amino acids
Amino-terminal tails are subjected to several forms of covalent modifications:
Acetylation of lysines
Phosphorylation of serines
Mono, di, or trimethylation of lysines
Chromatin
DNA-histone complex contained in nucleus
Chromatin condenses to form ___________.
Chromosomes
Centromere
DNA sequence that links sister chromatids
What are the four major configurations of chromosomes?
- Metacentric - centromere is centered
* Results in similar arm lengths - Submetacentric - centromere is off-center
* Results in different arm lengths - Telocentric - centromere is at end of chromosome
* Results in long, single arms - Acrocentric - centromere located near end of chromosome
* Stalk and bulb appearance
* E.g., human Y chromosome
Describe telomeres: what they are, where they are located, and what is their function?
- consist of noncoding repetitive nucleotide sequences
- Located at chromosome tips
- Protect and stabilize ends of chromosomes
Origins of replication
sequences of nucleotides that determine where DNA replication begins
How many origins of replication are in human chromosomes?
~ 30,000
Why do purines always base pair with pyrimidines?
- Purines: double ring structure
- Pyrimidines: single ring structure
- Two pyrimidines: distance too large to form hydrogen bonds
Hydrogen bonds between base pairs form when _________ atom is ~2 Å away from an __________ atom (e.g., _____ and ____)
Hydrogen; electronegative; N; O
Nucleosome
basic structural and functional unit of chromatin
Association of DNA into nucleosomes shortens DNA length _______.
7-fold
H1
non-core histone protein
30-nm fiber
Contains any chromatin region not being actively transcribed/replicated
Bead-on-a-string form
Contains chromatin regions actively being accessed
Under a microscope, euchromatin is seen as…
Lightly stained regions
Why is euchromatin seen as lightly stained regions under a microscope?
Euchromatin retains fewer stained particles
List the Writers.
- Methyltransferases
* Acetylases
* Kinases
List the Erasers.
- Demethylases
* Deacetylases
* Phosphatases
What did the Watson-Crick model (1953) propose?
DNA is made up of two strands of nucleotides that twist around each other to form a right-handed helix
DNA strands are _______.
Antiparallel
What does it mean for DNA strands to be antiparallel?
3’ end of one strand faces 5’ end of other strand (3’-5’ and 5’-3’)
What does the Watson-Crick model say about base pairing?
Bade pairing takes place between a purine and a pyrimidine
Introns and exons are transcribed into ________.
pre-mRNA
_____ mRNA is translated into a protein.
Mature
What is the function of H1 and what is the result of this function?
Changes DNA path as it exist nucleosome -> further compacts chromatin
What are 30-nm fibers?
Short, thick fiber of nucleosomes stacked on top of each other that are 30 nm in diameter
30-nm fibers are best explained by which model?
Solenoid model
Erasers
Enzymes that catalyze removal of chemical groups from amino-terminal tails
Writers
Enzymes that catalyze addition of chemical groups from amino-terminal tails
What is the histone code?
Histone modifications encode signals for cells
Give examples of signals encoded by modifications in the histone code.
- DNA damage and need for repair
- Gene expression
- Gene silencing
- Chromatin modification
Readers
Regulatory proteins that decode histone codes
How do readers work?
