Chapter 12 Flashcards
Define: Nucleosomes
lowest level of chromosome organization
A chromosome consists of:
- chromatin fibers
- histones
A chromosome contains one:
Single, continuous DNA molecule
What are nucleosomes?
DNA and histones are organized into nucleosomes
Structure of histones contain: (2)
- histone H1
- core complex forming octamer
What is the purpose of histone Hi?
Serves as a linker
What does the core complex in nucleosomes consist of?
H2A, H2B, H3, H4 forms an octamer
What is the purpose of a core complex?
DNA wraps itself around the core complex
What is histone modifaction?
One mechanism to alter character of nucleosomes
What can mediate DNA transcription, compaction, replication, recombination, and repair?
Histones, regulatory proteins, and enzymes
What groove faces the histone core?
Minor groove
What does each core histone have extending from it?
Flexible N-terimus tail
What part of the histone is subject to modification?
The histone tale (N-terminus tail)
Define: Cohesion
Holding replicated DNA molecules together during mitosis which mutations DNA loops
Describe the Chromatin structure
Gathered into series of large, supercoiled loops, compacted into thicker fibers
What is the packing rate of chromatin?
10,000:1, 1microm mitotic chromosome contains 1 cm of DNA
What is heterochromatin?
Compacted mitotic chromosomes, often with less function
When does heterochromatin form?
After mitosis, condensed during interphase
What is constitutive heterochromatin?
Remains condensed at all times, consists of highly repeated sequences and few genes
Where is constitutive heterochromatin found?
Mostly around centromeres and telomeres
What is facultative heterochromatin?
Inactivated in certain phases of life, found in one of the X chromosomes as Barr Body or heterochromatic clump
What is a Barr Body?
An inactive X chromosome in individuals that have two X chromosomes
What is the reason for X chromosome inactivation?
To silence one of the X chromosomes in genetic females
What is X chromosome inactivation also known as?
Heterochromatization
Which X chromosome is silenced? The paternal or maternal?
Either, it is randomized
When is an X chromosome silenced?
Occurs during early embryonic development and leads to inactivation of genes on that chromosome
What is the histone code hypothesis?
States the activity of a chromatin region depends on degree of chemical modification of histone tails
What is the function of histone tails?
- serve as docking sites to nonhistone proteins
- alter way histones and neighbour nucleosomes interact
Where are the majority of modified amino acids on histones?
On the N-termini of H3 and H4
Inactive, heterochromatic X chromosome results in
Deacetylated histones
Active, euchromatic X chromosomes results in
Normal level of acetylation
Describe the structure of mitotic chromosomes
Highly condensed chromatin in mitotic cells
Define: Karotype
Preparation of homologous pairs ordered according to size, used to see chromosomal abnormalities
What is a telomere?
A region of sequences that has a group of specialized proteins at the end of a DNA molecule
What is an end-replication problem?
If cells are not able to replicate ends of DNA, chromosomes would become shorter with each round of cell division
How are new repeats added to DNA?
Telomerase
What is telomerase?
A reverse transcriptase that synthesized DNA from DNA template
What are 3 significant aspects of telomeres?
- required for complete chromosome replication
- form caps that protect chromosomes from nucleases and other destabilizing influences
- prevent ends of chromosomes from fusing with each other
Where are centromeres found?
Markedly indented chromosomal site
What is a centromere?
A constricted region of a chromosome and helps the cell divide up its DNA, also the region where the cell’s spindle fibers attach
Genes are moved to sites within the nucleus, site is where transcription machinery is concentrated and genes involved in same response often become co-localized describes what?
Transcription factories
What are topologically associated domains?
Series of regions where DNA within such a region tends to interact strongly with other DNA in the same region than it does with parts of genome
What are speckles?
Function as dynamic storage depots that supply factors for use at nearby sites of transcription
What is transcription?
Process by which RNA is formed from a DNA template
What is translation?
Process by which proteins are synthesized in the cytoplasm from an mRNA template
What is an operon?
Functional complex of genes containing the information for enzymes of a metabolic pathway
What does an operon include?
- structural genes
- promoter
- operator
What do structural genes in an operon do?
Code for enzymes
What do promoters do in an operon?
Where RNA pol blends
What does the operator do in an operon?
Site next to promoter where regulatory protein can bind
What is a repressor?
Binds to a specific DNA sequence to determine whether or not a gene is transcribed, RNA pol is unable to bind to promoter is repressor is bound
What is a regulatory gene?
Encodes repressor protein
When are genes turned off?
After interactions with regulatory proteins
Regulation of gene expression occurs on 4 levels:
1) Transcriptional control
2) Processing control
3) Translational control
4) Posttranslational control
What is differential translation?
Mechanism by which eukaryotic cells determine which proteins are synthesized
What are DNA microarrays?
Can monitor the expression of thousands of genes simultaneously
Transcription factors contains what two things?
- DNA binding domain
- activation domain
What are response elements?
PEPCK is a key element controlled by variety of transcription factors
What regulates the initiation of transcription?
TATA box
What are enhancers?
DNA elements that stimulate transcription
What are insulators?
Promoter and its enhancers can be codoned off from other elements by sequences that are insulated
What are coactivators?
Transcriptional activator bound to an enhancer can stimulate transcription through coactivators
What can alter chromatin structure?
Coactivators
What are histone deacetylases (HDACs)?
Remove acetyl groups and repress transcription, act as corepressors
What is alternative splicing?
Pattern of intron removal can allow for multiple protein products from same gene, allows different combinations of exons in final mRNA product
How can nucleotides be converted to other nucleotides?
mRNA editing
What can mRNA editing create?
new splice sites, stop codons, amino acid substitution
Where are mRNAs, tRNAs, and ribosomal subunits manufactured?
Nuclear envelope
What is the nuclear lamina?
A thin meshwork composed of intermediate filaments that lines the inner surface of the nuclear envelope
What is the nuclear localization signal?
Sequence of aas in a protein that is recognized by a transport receptor leading to translocation of the protein from the cytoplasm to the nucleus
What do transport receptors include?
Importins and exportins
What are importins?
They move molecules from cytoplasm into nucleus
What are exportins?
They move molecules from nucleus to cytoplasm
Synthesis of specialized RNAs broad overview:
Synthesized in nucleus, modified in cytoplasm, function in nucleus
What do RNAs move through the cell as?
Ribonucleproteins
What can influence the lifetime of mRNA?
poly (A) tail length
What are P-bodies?
Cytoplasmic granules in which RNA is stored or processed for degradation
What are miRNAs roles in development?
- patterning of nervous system
- control of cell proliferation and death
- leaf and flower development in plants
What is the function of piRNAs?
Suppress transposon movement
How do miRNAs suppress gene expression? (4 things)
- promoting deadenylation and degradation
- inhibit initiation of translation
- inhibit elongation
- activate degradation of nascent peptides
What are proteosomes’ function?
Degradation of proteins is carried out
