Transcript Chapter 10.2

Gene Regulation and Structure
Grade 10 Biology
Spring 2011
 Describe
how the lac operon is turned on
and off
 Summarize the role of transcription factors
in regulating eukaryotic gene expression
 Describe how eukaryotic genes are organized
 Evaluate three ways that point mutations
can alter genetic material
 Prokaryotes
have about 2,000 genes
 Humans have about 30,000 genes
 Not all of genes are transcribed and
translated at the same time

So as not to waste energy and materials
 Both
are able to regulate gene expression
depending on cell’s needs
 E.


Coli
Prokaryote
Gene regulation well undestood- lac operon gene
 E.
Coli is in the intestinal tract
 Lactose from milk enters and becomes
available to E. Coli
 E. Coli (bacteria) can absorb lactose and
break it down for energy
 Recognizing, consuming, and breaking
down lactose, into glucose and galactose,
requires 3 different enzymes on 3 different
genes
3
lactose metabolizing genes are located
next to each other
 Controlled by the same promoter site
 On-off switch


“turns on” (transcribes and then translates) the 3
genes when lactose is present
“turns off” genes when lactose is not available
 Operator:


Piece of DNA that overlaps promoter site and
serves as on-off switch
Able to control RNA polymerase’s access to 3
lactose metabolizing genes
 Promoter:

Area in which RNA polymerase binds and allows
the genes to be transcribed
 Repressor


protein:
Protein that binds to an operator and physically
blocks RNA polymerase from binding to promoter
site
Stops transcription of genes in operon
 Operon:

A group of genes that code for the enzymes
involved in the same function, their promoter
site, and the operator that controls them all
 Lac

Operon:
Operon that controls the metabolism of lactose
 Repressor
protein turns the operon off
 Repressor protein binds to the operator and
blocks RNA polymerase from binding to the
promoter site
 Blocking of RNA polymerase stops the
transcription of genes in the operon
 Lactose
binds to repressor protein and
changes repressor proteins shape
 Change of shape causes repressor protein to
fall off of the operator
 Now the RNA polymerase is free to bind to
the promoter (no longer blocked)
 RNA polymerase can transcribe the genes
that code for the lactose metabolizing
enzymes
 By
producing the enzymes only when the
nutrient is available, the bacterium (E. coli)
saves energy
 Lets
watch a video to review the lac operon!
 Contain
more DNA than prokaryotes
 Must continually turn genes on and off
 Operons are not common in eukaryotes
 Instead, genes with related functions are
often scattered on different chromosomes
 Because
there is a nuclear envelope that
physically separates transcription from
translation more opportunities for gene
regulation
 Gene




regulation can occur:
Before transcription
During transcription
After transcription
And after mRNA leaves the nucleus or after
translation, when protein is functional
 Most
gene regulation in eukaryotes controls
the onset of transcription

When RNA polymerase binds to a gene
 Use
regulatory proteins- called transcription
factors
 But many more proteins involved and more
complex
 Transcription


factors:
Help arrange RNA polymerases in the correct
position on the promoter
Gene can be influenced by many different
transcription factors
Enhancer: sequence of DNA that can be bound by a
transcription factor
 Located thousands of nucleotide bases away from
promoter
 Loop in DNA may bring enhancer and its attached
transcription factor (activator) into contact with the
transcription factors and RNA polymerase at the
promoter

 In
eukaryotes many genes are interrupted by
introns
 Introns: long segments of nucleotides that
have no coding information
 Exons: portions of a gene that are translated
(expressed) into proteins
 After
gene is transcribed, introns in mRNA
are cut out by splicosomes
 Splicosomes: complex assemblies of RNA and
protein
 Exons that remain are “stitched” back
together by slicosome to form a smaller
mRNA molecule
 mRNA is then translated
 Each
exon encodes part of protein
 By having introns and exons cells can
occasionally shuffle exons to make new
genes
 Play an evolutionary role
 Thousands of proteins that occur seem to
have arisen from a few thousand exons
 Some genes exist in multiple copies
 Mutation:

change in the DNA of a gene
Rare
 Mutations
in gametes can be passed on to
offspring, those in body cells (somatic cells)
cannot
 Gene
Rearrangements:
mutations that move an
entire gene to a new
location


Disrupt genes function, gene is
exposed to new regulatory
conditions
Ex. You move to France and
can’t speak French
 Two
1.
2.
types of Gene Rearrangements:
Tranposition: genes are carried by moving
transposons
Chromosomal Rearrangement: portions of the
chromosome containing a gene may be
rearranged during meiosis
 Gene
Alterations: mutations that change a
gene


Usually result in the placement of the wrong
amino acid during protein assembly
Usually disrupts protein’s function
 Three
types of Gene Alterations:
Point Mutations: single nucleotide changes
Insertion Mutation: sizable length of DNA is
inserted into a gene
1.
2.

Often result when mobile segments of DNA
(transposons) move randomly from one position to
another on a chromosome
Deletion Mutation: segments of gene are lost
3.

Often during meiosis
Point Mutation
Deletion Mutation
Insertion Mutation
 Genetic
message is read as a series of triplet
nucleotide
 Insertions and deletions can upset the triplet
groupings
 Ex. Delete the C from this sentence, keep
letters in triplets


THE CAT ATE
THE ATA TE  meaningless
 Frameshift
Mutation: mutation that causes
gene to be read in the wrong 3-nucleotide
sequence
 http://www.youtube.com/watch?v=gqvYOr78
THo
Activity Modeling Introns and Exons (p. 218)
 Procedure:

Place a 15-20cm strip of masking tape on your desk.
Tape represents a gene.
 Use 2 colours to write the words APPROPRIATLY
JOINED on the tape exactly as shown. Space the
letters so that they take up the entire length of the
tape. The segments in one colour represent introns;
those in the other colour represent exons.
 Lift the tape. Working from left to right, cut apart
the groups of letters written in the same colour. Stick
the pieces of tape to your desk, making two strips
according to colour and joining the pieces in their
original order.

 Activity
Modeling Introns and Exons (p. 218)
 Analysis


Determine from the resulting two strips which
strip is made of introns and which is made of
exons
Predict what might happen to a protein if an
intron were not removed