Transcript Slide 1

Unit 3 Review
This version is for posting to the
class web site.
Genes are located on chromosomes and
are the basic unit of heredity that is
passed on from parent to child, through
generations.
A. Explain how a chromosome mutation
could occur and why mutations are
detrimental to the organism in which they
take place.
B. Explain why human males may suffer
from having just one copy of the X
chromosome, while females have two.
5 end
O
OH
P
–O
O
H2C
Remember:
phive-phosphate
What do 3 and 5
stand for???
What does
antiparallel mean?
O
O
P
–O
O
H2C
OH
O
O
A
T
O
O
O
P
–O
O
H2C O
O
O
P
–O
O
H2C
3 end
Hydrogen bond
G
C
C
O CH2
O
O–
P
O
O
G
A
3 end
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O
CH2
O
O–
P
O
O
O
CH2
O
O–
P
O
O
T
OH
Figure 16.7b
O CH2
O O–
P
O
O
(b) Partial chemical structure
5 end
Punnett Squares
• Punnett squares help us
visualize segregation of
allelles:
All F1’s show
dominant trait
3:1 F2 ratio on eye
color trait indicates
heterozygous cross.
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Operons are ___karyotic
lac operon
DNA
lacl
lacz
3
mRNA
5
lacA
RNA
polymerase
mRNA 5'
5
mRNA
-Galactosidase
Protein
Allolactose
(inducer)
lacY
Permease
Transacetylase
Inactive
repressor
(b) Lactose present, repressor inactive, operon on. Allolactose, an isomer of lactose, derepresses
the operon by inactivating the repressor. In this way, the enzymes for lactose utilization are induced.
Why can’t this dad
give hemophilia to his
sons?
How could a girl end
up with hemophilia?
Crossing Over
Nonsister
chromatids
Prophase I
of meiosis
• Crossing over:
Tetrad
– when does this
happen?
– the closer two
alleles are on a
chromosome, the
____ chance of
being separated by
crossing over.
Metaphase I
Chiasma,
site of
crossing
over
Metaphase II
Daughter
cells
Figure
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Cummings
Recombinant
chromosomes
How can you show that this pedigree is
of an autosomal recessive trait?
What’s the diff between autosomal &
sex-linked?
Multiple Alleles
• Most genes exist in more than two allelic forms
– Ex: ABO blood
groups
– Which type of
blood cell(s)
would be rejected
by a person with
type B blood?
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mom
dad
A
? A
? A
B
B
B
What is Dad if 50% of offspring come out type A, and 50%
come out type B?
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If Y is a lethal allele, and it’s dominant,
who will survive here?
Can you think of an example of a lethal
dominant that does persist in the
population
because it
doesn’t kill till
middle age?
12. Y y
Y YY Yy
y Yy yy
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Sporophytes
produce __ploid
______s by
___osis.
Gametophyes
produce __ploid
_______s by
___osis.
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• What is Independent assortment?
–
pairs of maternal and paternal homologues sort into
gametes independently of the other pairs
Key
Maternal set of
chromosomes
Possibility 1
Paternal set of
chromosomes
Two equally probable
arrangements of
chromosomes at
metaphase I
Possibility 2
Metaphase II
Daughter
cells
Figure 13.10
Combination 1 Combination 2
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Combination 3 Combination 4
W=waxy, w=dull; G=green, g=yellow
•You can do a dihybrid Punnett for this
problem, (WwGg x WwGg) or…
– find probability of each character
separately (dull and green)
– then, multiply probabilities of dull
and green together.
– dull Green = wwGG or wwGg
F1
W
w
W
WW
Ww
w
Ww
ww
x
F1
G
g
G
GG Gg
g
Gg
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gg
= ¼ x ¾ = 3/16
3/16 x 144 = 27
How are these
virusus the same?
How are they
different?
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Same in all eukaryotes, from
yeast to you. KNOW IT!
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What are
restriction
enzymes?
What are
they used
for?
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Movement of Transposons and Retrotransposons
• Eukaryotic
transposable
elements are of two
types
– Transposons,
which move within a
genome by means
of a DNA
intermediate
Transposon
DNA of genome
New copy of
transposon
Transposon
is copied
Insertion
Mobile transposon
(a) Transposon movement (“copy-and-paste” mechanism)
– Retrotransposons,
which move by
means of an RNA
intermediate
Figure 19.16a, b
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Retrotransposon
New copy of
retrotransposon
DNA of genome
RNA
Reverse
transcriptase
(b) Retrotransposon movement
Insertion
DNA Methylation
• methylation of cytosines on
the DNA strand lead to tight
packing & reduces
transcription
• methylation patterns are
copied during mitosis
• what do we call it if
methylation is passed to the
next generation?
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KNOW
IT!
Figure 17.26
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• Histone acetylation …
– loosens chromatin structure and enhance
transcription
Unacetylated histones
Figure 19.4 b
Acetylated histones
(b) Acetylation of histone tails promotes loose chromatin structure that
permits transcription
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Lytic & Lysogenic phage
infections:
The Telemere problem in DNA Replication
• The ends of eukaryotic
chromosomes get
shorter with each
round of replication
5
Leading strand
Lagging strand
End of parental
DNA strands
3
Last fragment
Lagging strand
Previous fragment
RNA primer
5
3
Primer removed but
cannot be replaced
with DNA because
no 3 end available
3
for DNA polymerase
Telemerase can
restore these ends
Removal of primers and
replacement with DNA
where a 3 end is available
5
Second round
of replication
5
New leading strand 3
New lagging strand 5
3
Further rounds
of replication
Figure 16.18
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Shorter and shorter
daughter molecules
5
DNA Amplification:
Target
sequence
3
Genomic DNA
• PCR procedure:
– use specific primers
to bind to each end of
the segment you
want.
– use a heat resistant
DNA polymerase
– after about 20 cycles,
target DNA (white
boxes) greatly
outnumber longer
strands.
3
1
Cycle 1
yields
2
molecules
2
Denaturation:
Heat briefly
to separate
DNA strands
5
3
3
5
Annealing:
Cool to allow
primers to
Cycle 3
yields 8
molecules;
2 molecules
(in white boxes)
match target
sequence
Primers
hydrogen-bond.
Extension:
3 DNA
polymerase
adds
nucleotides
to the 3 end of
each primer
Cycle 2
yields
4
molecules
5
New
nucleotides
Normal  -globin allele
• Restriction
fragment analysis
– Is useful for
comparing two
different DNA
molecules, such
as two alleles
for a gene
201 bp
175 bp
DdeI
DdeI
Large fragment
DdeI
DdeI
Sickle-cell mutant -globin allele
Large fragment
376 bp
DdeI
DdeI
DdeI
(a) DdeI restriction sites in normal and sickle-cell alleles of
-globin gene.
Normal
allele
Sickle-cell
allele
Large
fragment
376 bp
201 bp
175 bp
Figure 20.9a, b
(b) Electrophoresis of restriction fragments from normal
and sickle-cell alleles.
How many cuts to get 9 pieces?
Why would we want
to “steal” a gene and
put it in a bacterial
plasmid?
How could you do it?
RNA Polymerase Binding and Initiation of Transcription
• Promoters signal
the initiation of
RNA synthesis
DNA
RNA PROCESSING
Pre-mRNA
mRNA
Ribosome
TRANSLATION
1 Eukaryotic promoters
Polypeptide
Promoter
5
3
• Transcription
factors
TRANSCRIPTION
TATA box
– Help eukaryotic
RNA polymerase
bind to promoter
sequences
3
5
T A T A A AA
AT AT T T T
Start point
Template
DNA strand
Transcription
factors
5
3
3
5
3 Additional transcription
factors
RNA polymerase II
5
3
Transcription factors
3
5
5
RNA transcript
Figure 17.8
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Transcription initiation complex
• The ribosomal subunits
– Are constructed of proteins and RNA
molecules named ribosomal RNA or rRNA
Figure 17.16a
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• The DNA template (gene) determines the order
of bases in the mRNA transcribed alongside.
• mRNA determines the order of Amino Acids
during translation
Gene 2
DNA
molecule
Gene 1
Gene 3
DNA strand 3
5
A C C A A A C C G A G T
(template)
TRANSCRIPTION
mRNA
5
U G G U U U G G C U C A
Codon
TRANSLATION
Protein
Figureas17.4
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Trp
Amino acid
Phe
Gly
Ser
3
• Spliceosomes remove the __ons from pre mRNA
RNA transcript (pre-mRNA)
5
Intron
Exon 1
Exon 2
Protein
1
Other proteins
snRNA
snRNPs
sn = small nuclear
Spliceosome
2
5
Spliceosome
components
Figure 17.11
3
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mRNA
5
Exon 1
Exon 2
Cut-out
intron
Know how to use this
table to determine
which amino acids the
mRNA is coding for!
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Substitutions
• A base-pair substitution
can cause
– missense or
– nonsense
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• DNA replication is
semiconservative…
– Each new daughter
molecule has one old
strand and one newly
made strand
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