Transcript Wednesday, September 5

19.1
1.
Describe the structure of a
nucleosome, the basic unit of DNA
packaging in eukaryotic cells.
19.1
1.
•Eight histone proteins (2 each of
4 different kinds)
•DNA wound around them
•Linker DNA between histones
19.1
2.
What chemical properties of
histones and DNA enable these
molecules to bind tightly together?
19.1
2.
•Histones contain many basic
amino acids with + charges
•Phosphate groups in DNA’s
backbone are negatively charged
19.1
3.
In general, how does dense packing
of DNA in chromosomes prevent
gene expression?
19.1
3.
RNA polymerase cannot physically
get at the DNA
19.2
1.
In general, what is the effect of
histone acetylation and DNA
methylation on gene expression?
19.2
1.
•Histone acetylation usually flags
genes for expression
•DNA methylation usually flags
them for not being expressed
19.2
2.
Compare the roles of general
and specific transcription factors
in regulating gene expression.
19.2
2.
General transcription factors
Assemble transcription initiation
complex for promoters of all genes
Specific transcription factors
Bind to control elements for just one
gene and either activate or repress it
19.2
3.
If you compared the nucleotide
sequences of the distal control
elements in the enhancers of
three coordinately regulated
genes, what would you expect to
find? Why?
19.2
3.
•All three genes have very similar
sequences in the control elements
of their enhancers
•That way, the same specific
transcription factors can bind to
all three
19.2
4.
Once mRNA encoding a
particular protein reaches the
cytoplasm, what are four
mechanisms that can regulate
the amount of the active protein
in the cell?
19.2
4.
1.
2.
3.
4.
Degradation of mRNA
Regulation of translation
Activation of protein
Degradation of protein
19.3
1.
Compare the usual functions of
proteins encoded by protooncogenes with those encoded by
tumor-suppressor genes.
19.3
1.
•Product of proto-oncogene
stimulates cell division
•Product of tumor-suppressor
gene inhibits cell division
19.3
2.
Explain how the types of mutations
that lead to cancer are different for
a proto-oncogene and a tumorsuppressor gene.
19.3
2.
•Mutation of proto-oncogene
makes overactive protein
•Product of tumor-suppressor
makes inactive protein
19.3
3.
Under what circumstances do we
consider cancer to have a
hereditary component?
19.3
3.
•Oncogenes
•Mutant alleles of tumor-supressor
genes
19.4
1.
Discuss the characteristics that
make mammalian genomes larger
than prokaryotic genomes.
19.4
1.
•5x – 15x more genes
•10,000x more non-coding DNA
•Introns make genes 27% longer
on average
19.4
2.
How do introns, transposable
elements, and simple sequence
DNA differ in their distribution in the
genome?
19.4
2.
•Introns are within coding regions of
genes
•Transposable elements are
scattered throughout
•Simple sequence DNA is mostly at
telomeres and centromeres
19.4
3.
Discuss the differences in the
organization of the rRNA gene
family and the globin gene families.
How do these gene families benefit
the organism?
19.4
3.
rRNA
•Many indentical
genes in tandem
•Lots of genes
means lots of
rRNA can be
made
Globin
•Many nonidentical genes
near each other
•Different genes
means different
kinds of globin can
be made at
different stages
of development
19.5
1.
Describe three examples of errors
in cellular processes that lead to
DNA duplications.
19.5
1.
1. Faulty cytokinesis can make
two entire copies of genome
2. Errors in crossing over
3. Backward slippage during DNA
replication copies some of it
twice
19.5
2.
What processes are thought to
have led to the evolution of the
globin gene families?
19.5
2.
•Gene duplication
•Divergence by mutation
•Movement of genes to different
chromosomes
19.5
3.
Look at the portions of the fibronectin
and EGF genes shown in the figure
below. How might they have arisen?
19.5
3.
Errors in crossing over
19.5
4.
What are three ways
transposable elements are
thought to contribute to the
evolution of the genome?
19.5
4.
•Scattered homologous transposons
allow recombination between
chromosomes
•Transposons in regulatory areas
change expression of genes
•Transposons carry genes to new
places in genome
•Transposons carry exons , making
new functional domains in existing
genes