2015 Pearson Education, Inc. Chromosome structure and chemical
modifications can affect gene expression DNA packing
Slide 3
2015 Pearson Education, Inc. Methylation- Chemical modification
of DNA bases or histone proteins can result in epigenetic
inheritance Chromosome structure and chemical modifications can
affect gene expression
Slide 4
2015 Pearson Education, Inc. Early Embryo Adult X chromosomes
Cell division and random X chromosome inactivation Active X
Inactive X Two cell populations Orange fur Inactive X Active X
Black fur Allele for orange fur Allele for black fur Chromosome
structure and chemical modifications can affect gene expression X
inactivation
Slide 5
The Control of Gene Expression Each cell in the human contains
all the genetic material for the growth and development of a human.
Some of these genes will be need to be expressed all the time.
These are the genes that are involved in of vital biochemical
processes such as respiration. Other genes are not expressed all
the time. They are switched on an off at need.
Slide 6
Operons An operon is a group of genes that are transcribed at
the same time. They usually control an important biochemical
process. They are only found in prokaryotes.
Slide 7
Different ways to Regulate Metabolism block transcription
Feedback inhibition
Slide 8
Tryptophan operon Repressor is inactive alone
Slide 9
Slide 10
Lactose operon Repressor is active alone
Slide 11
Regulator gene lac operon Operator site zya DNA I O Repressor
protein RNA polymerase Blocked Lactose absent
Slide 12
Promotor site zya DNA I O Promotor site zya DNA IO
Transcription Activator protein steadies the RNA polymerase Lactose
present
Slide 13
2015 Pearson Education, Inc. Complex assemblies of proteins
control EUKARYOTIC transcription In eukaryotes, activator proteins
seem to be more important than repressors. Thus, in multicellular
eukaryotes, the default state for most genes seems to be off. A
typical plant or animal cell needs to turn on and transcribe only a
small percentage of its genes. Eukaryotic RNA polymerase requires
the assistance of proteins called transcription factors. RNA
polymerase then attaches to the promoter, and transcription
begins.
Slide 14
2015 Pearson Education, Inc. Animation: Initiation of
Transcription
Slide 15
2015 Pearson Education, Inc. EnhancersPromoter Gene DNA
Transcription factors Activator proteins DNA-bending protein Other
proteins RNA polymerase Bending of DNA Transcription
Slide 16
2015 Pearson Education, Inc. Eukaryotic RNA may be spliced in
more than one way Alternative RNA splicing produces different mRNAs
from the same transcript and results in the production of more than
one polypeptide from the same gene. In humans, more than 90% of
protein-coding genes appear to undergo alternate splicing.
Slide 17
2015 Pearson Education, Inc. Animation: RNA Processing
Slide 18
2015 Pearson Education, Inc. Small RNAs play multiple roles in
controlling gene expression Only about 1.5% of the human genome
codes for proteins. (This is also true of many other multicellular
eukaryotes.) Another small fraction of DNA consists of genes for
ribosomal RNA and transfer RNA. A flood of recent data suggests
that a significant amount of the remaining genome is transcribed
into functioning but non-protein-coding RNAs, including a variety
of small RNAs.
Slide 19
2015 Pearson Education, Inc. Small RNAs play multiple roles in
controlling gene expression microRNAs (miRNAs) can bind to
complementary sequences on mRNA molecules either degrading the
target mRNA or blocking its translation. RNA interference (RNAi) is
the use of miRNA to artificially control gene expression by
injecting miRNAs into a cell to turn off a specific gene
sequence.
Slide 20
2015 Pearson Education, Inc. Chromosome DNA unpacking Gene DNA
Exon N UCLEUS Splicing Intron Addition of a cap and tail RNA
transcript mRNA in nucleus Tail Cap mRNA in cytoplasm Breakdown of
mRNA Cleavage, modification, activation Breakdown of protein Amino
acids Broken-down mRNA Polypeptide Active protein C YTOPLASM The
flow of genetic information from a chromosome to a protein is
controlled at several points, just as the flow of water through
pipes is controlled by valves. Transcription Translation
