Download DNA replication and inheritance File

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DNA Replication and
Inheritance
Topics 2.5 and 2.6
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Specification topic 2
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11 Describe DNA replication (including the role of DNA
polymerase), and explain how Meselson and Stahl’s classic
experiment provided new data that supported the accepted
theory of replication of DNA and refuted competing theories.
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15 Explain how errors in DNA replication can give rise to
mutations and explain how cystic fibrosis results from one of
a number of possible gene mutations.
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DNA Synthesis
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Read page 86
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What happens if there is a mistake during translation?
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What happens when there are inherited genetic conditions
(mistakes in DNA)?
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When do these mistakes in DNA arise?
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Define a mutation- (Not on page 86). Give an example
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DNA Replication- key words
• http://www.susanahalpine.com/anim/Grolier_Anims/DNA.htm
• http://www.youtube.com/watch?v=zdDkiRw1PdU
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Semi-conservative
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Complementary bases
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DNA
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H bonds
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Unwind
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Both
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Strands
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DNA polymerase
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Separate
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Condensation
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H bonds
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Phosphodiester bonds
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Helicase
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Two identical DNA molecules
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Each DNA molecule- One old
and one new strand
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DNA mononucleotides
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Steps of DNA Replication
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Animation:
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http://www.susanahalpine.com/anim/Grolier_Anims/DNA.htm
http://www.youtube.com/watch?v=zdDkiRw1PdU
1.
DNA unwinds and strands separate : DNA helicase break H
bonds between complementary bases.
2.
DNA mononucleotides pair with the complementary exposed
bases on each strand.
3.
H bonds form between new and old bases.
4.
Polymerization forms new strand, this is catalyzed by DNA
polymerase through condensation reactions.
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2 DNA molecules which are exact copies: Each molecule
contains 1 old and 1 new strand
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Semi-conservative
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Semi- conservative method
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Draw DNA replication
occuring three timesUse red for the original
strands you start with
and blue for any new
strands formed.
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How do we know how DNA is
replicated?
What other possible ways could replication occur? How do we
know DNA is copied by the semi-conservative method? Use
the same colour code to show the other possible methods.
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Meselson-Stahl Experiment
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Read page 87-88
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http://www.sumanasinc.com/webcontent/animations/content/me
selson.html - stop at points to allow answering of these questions-
1.
What were the two different forms of Nitrogen?
2.
How can DNA containing these different forms be separated?
3.
All the nucleotides containing ____________________ were
incorporated into the original DNA (old DNA) in generation
zero.
4.
«New» DNA contained nucleotides made of ______________
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Meselson-Stahl Experiment
1.
Draw the results seen by Meselson and Stahl for generations 0 to 2.
2.
Predict what the results would look like for generations 0 to 2 if the
conservative theory was correct. Remember that it is NOT.
3.
Predict the results for generations 3 and 4 with the semi-conservative
method- the correct one.
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Activity 2.15 Meselson and Stahl’s
experiment of DNA replication
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Go through the interactive tutorial
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Complete the worksheet.
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Mutations
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What are the consequences of mutations?
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Order of the bases changes 
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order of the amino acids changes(primary structure) 
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altered tertiary structure 
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altered 3D shape 
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non-functioning protein
Do all mutations have this effect? Explain.
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No………..non-coding DNA
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Some mutations - silent (not change 10 sequence- degenerative
code)(answer not in book)
Now complete questions Q2.29 and Q2.30
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Sickle Cell Anemia-
reading comprehension
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Read pages 88-89
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Which protein is affected? What is its function?
 Haemoglobin,: carry O2.
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Does hemoglobin have a quaternary structure?
 Yes, 4 polypeptide chains.
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What type of mutation occurs in sickle cell anemia?
 substitution, A replaces T
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Is it a silent mutation? Explain
 No, non-polar amino acid replaces a polar amino acidchanges tertiary structure —› 3D shape —› function.
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What is the end effect of this mutation?
 Hemoglobin less soluble, carries less O2,can block blood
vessels.
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Cystic Fibrosis
Which protein is affected?
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What type of mutation causes it?
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CFTR protein
Hundreds of different types
What is the most common mutation? Describe it.
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DF508, deletion of 3 nucleotides —› loss of an amino acid —› altered
tertiary structure- change in shape- loss of function
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What type of molecule is phenylalanine?
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What are the possible effects of the different types of mutation on
the CFTR protein?
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ATP cannot bind
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Channel cannot open
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Structure of channel changed and Cl- cannot flow through.
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Specification Topic 2
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16 Explain the terms gene, allele, genotype, phenotype,
recessive, dominant, homozygote and heterozygote, and
explain monohybrid inheritance, including the interpretation
of genetic pedigree diagrams, in the context of traits such as
cystic fibrosis, albinism, thalassaemia, garden pea height and
seed morphology.
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Revision
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What causes CF?
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Faulty CFTR protein leading to stickier mucus
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This is due to a mutation in the CFTR gene
+Inheritance
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Read pages 90-92 and define: Those in red were defined in topic 1.
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Homologous chromosome
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Locus
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Gene
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Allele
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Genotype
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Phenotype
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Homozygous
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Heterozygous
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Dominant allele
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Recessive allele
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Carrier
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Genetic pedigree diagram
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Activity 2.17a Example Genetic Cross
Cystic fibrosis is caused by a recessive allele. By looking at Claire’s family, we know that Claire
must be a carrier for the disease. Let’s assume Nathan is also a carrier and work out the chance of
their children having the disease or being a carrier.
Claire
Nathan
Parents’ phenotype
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________
Parents’ genotype
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________
Gametes’ genotypes
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________
_____________ Square
Offspring genotype ratio:
1_____:
2 ____:
Offspring phenotype ratio:
1 __________:
1 _____
2 ________:1 ________
CompareRatio
Probability
proportiong
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Inheritance
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Answer questions 2.31-2.32
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Activity 2.17
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Some other Human Genetic
Diseases
Reading and comprehension
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Explain the term monohybrid inheritance.
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Controlled by one gene
Name some other conditions controlled by one gene?
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Thalassaemia- abnormal manufacture of haemoglobin
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Albinism- lack of pigment
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Phenylketonuria- inability to metabolize phenylalanine resulting in
mental disorders
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Huntingdon’s- neurons degenerate affecting muscle coordination
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Achondroplasia- restricted growth
How are Huntingdon’s and Achondroplasia different from the
other examples? What is the significance of this?
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Caused by dominant allele, heterozygous genotype also has disease.