Lecture 11

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  • Created by: Katherine
  • Created on: 09-02-16 15:30
What are chromosomes made of?
Chromatin
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What is chromatin made of?
Protein and DNA
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What is chromatin?
It is an intricate form of packaging for DNA
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In order for transcription and replication to occur in a cell DNA must be what?
Packed in an organized manner to be accessible
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The organisation of DNA in the cell involves association with...
specific proteins (histones) and the formation of chromatin.
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Which is more complex, Eukaryotic chromatin or Prokaryotic?
Eukaryotic
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Each human chromosome contains a single linear ...
DNA helix
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Heterochromatin is...
highly condensed during interphase, it is not actively transcribed.
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Euchromatin is...
less condensed during interphase, able to be transcribed
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Where does packing being?
With the nucleosome - the basic unit of chromatin.
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What are histones?
Proteins with positively charged amino acids that bind to the negatively charged DNA. They play a key role in chromatin structure.
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During interphase, what form are most of the chromosomes in?
Euchromatin
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What does Euchromatin look like?
Looped domains of the 30nm chromatin fibre.
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During meiosis and mitosis, what happens to the chromatin?
It folds further (condenses)
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The highly condensed chromatin also occurs during interphase in some regions of the chromosome. What is this called?
Heterochromatin
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Which of Euchromatin and Heterochromatin is looser?
Euchromatin.
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Can Heterochromatin be transcribed?
It is too tightly packed (supercoiled)
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In both eukaroytes and prokaryotes, are genes always on?
No, they are continually be turned on and off in response to signals from their internal and external environments.
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In multicellular eukaryotes, cellular differentiation occurs. What is this?
Long term control of gene expression
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How many different cell types are in the human body?
>200
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How much does a cell express of its 30,000 genes at any given time?
3-5%
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When can regulation of gene expression occur?
At any step from gene to protein
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How else can gene expression be adjusted?
By chemical modification of chromatin
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What are the two types of chemical modification of chromatin?
DNA methylation and Histone acetlyation
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What is DNA methylation?
It is when methyl groups are attached to DNA bases.
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What does attaching methyl groups to the DNA bases do?
It triggers the formation of a compact chromatin structure
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Is DNA methylation associated with active or inactive DNA?
Inactive
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What does DNA methylation account for?
Genomic imprinting in mammals
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What is Histone acetylation associated with?
Gene activation
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What is Histone acetylation?
It is the attachment of acetyl groups (COCHE) to histones
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Do the acetylated histones grip DNA more or less tightly?
Less
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Acetylation is involved in the switching on or off of genes?
Switching on
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If DNA is methylated and histones are not acetyled, is the chromatin open or closed?
It is closed.
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If the DNA is unmethylated and histones are acetylated, is the chromatin open or closed?
It is open.
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How many types of different RNA polyermases are in Eukaryote?
3
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What is RNA polymerase I?
Ribosomal RNA
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What is RNA polymerase II?
Messenger RNA
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what is RNA polymerase III?
Small RNAs (tRNA)
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What causes transcription to begin?
When the RNA polymerase binds to a promoter
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What are promoters?
DNA sequences adjacent to the gene (upstream)
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What does the promoter determine?
It determines where the transcription of the gene is initiated, and the rate of transcription
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What is the TATA box?
A key part of the promoter, it provides the site of intial binding of the transcription initiation machinery, it is located 10-35 bp upstream of the transcription site.
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Before transcription can start, what must form:
A pre-initiation complex
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Can RNA polymerases bind to promoters on their own?
NO
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In order to with with the promoter, the RNA polymerase II must bind to...
TFIIF
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How is the rate of transcription modulated in Eukaryotes?
The interaction between the transcription initiation complex and the basal promoter is inefficient.
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The process of transcription is regulated by what?
Specific transcription factors - activators or repressors
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What do the activators or repressors do?
They bind to proximal control elements and distal control elements (enhancers).
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What are the grouping of proximal control elements and distal control elements called?
Enhancers
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How do enhancers work when they may be 1000s of base pairs from the promoter?
DNA folding occurs to bring the distal sequences into proximity with the promoter
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What is the modular structure of specific TFs?
They have separate DNA binding and transcriptional activation domains
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The transactivation domain is responsible for what?
For recruiting other proteins into the transcription factor complex
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How is processing of the primary transcript in Eukaryotes done?
By capping of the 5' end, polyadenylation of 3' end, splicing to remove introns
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How do regulatory proteins control intron-exon choices?
By binding to regulatory sequences within the primary transcript.
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Where are Dscam proteins located?
On the surface of a growing neuron
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What do Dscam proteins do?
They provide a cell recognition mechanism that regulated brain development.
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