notes-molecular genetics

8/6/2019 Notes-Molecular Genetics

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Molecular Genetics

The HOWof Heredity


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Why Study Molecular

Genetics?We now know a lot about patterns of

inheritance.Punnett Squares

Pedigrees

Many different types of inheritance


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Why Study Molecular

Genetics?Now we need to understand howthese things happen.

What makes a genotype show up as aphenotype?How can a DNA code cause you to

have the traits you have?How do scientists study genes and

proteins?What about mutations?


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DNA Structure

We begin our study ofmolecular genetics withthe molecule of heredity:DNA

DNA structure double helix repeating units =

nucleotides Adenine (A), Thymine

(T), Cytosine (C), andGuanine (G)


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DNA Structure

The genetic code:nucleotide sequenceC, A, T and Gs.

A portion of DNA thatcodes for a particulartrait is called a gene.

Base pairing: A T, C

G. DNA replication

protein synthesis.


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RNA StructureRNA is a single-stranded chain ofnucleotides.

Nitrogenous BasesAdenine

Cytosine

Guanine

Uracil


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Types of RNA

messenger RNA (mRNA). Copies theDNA code and carries it to the ribosome.

ribosomal RNA (rRNA). A building ofribosomes: machinery for synthesizingproteins by translating mRNA.

transfer RNA (tRNA). RNA moleculesthat carry amino acids to the growingpolypeptide.


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Gene Expression

How is an organisms genetic codecontained in its DNA?

Gene Expression: Living thingsread and use encoded DNA. DNAcode is used to build proteins.

Proteins are responsible for manyof an organisms characteristics.


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The Many Functions of

ProteinsStructurea. Keratin skin, hair, feathers

b. Actin and Myocin muscle

movementc. Collagen connective tissue


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The Many Functions of

ProteinsHemoglobin carry O2 on RBC

Hormones (chemical signals)

a. Insulin regulate sugar uptake

b. Epinephrine (adrenaline) fight or flight stress response

c. Estrogen/Testosterone sexcharacteristics


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Flow of Genetic

Information

Most genes encode the information for

the synthesis of a proteinThe sequence of bases in DNA codes forthe sequence of amino acids in proteins


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Flow of Genetic

Information


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Central Dogma of Molecular Biology

Protein

Synthesis

Mitosis ONLY!!!

Transcription:

DNA mRNA

Translation:

mRNA aminoacids


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In Prokaryotes

Transcription and translation happen atthe same time.


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In Eukaryotes.

Transcription in the nucleus

Translation in cytoplasm at ribosome

DNA stays in the

nucleus.

an evolutionaryadaptation!!


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The Genetic Code

mRNA transcribes DNAThree mRNA bases = a codonWill code for 1 amino acid

Carried to ribosome by tRNA

Why 3? Why not 1 or 2?

UAA =

STOPAUG =

GO


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The Genetic Code

S t t d ith


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Suppose you started withthe following strand of

DNA:C A T T C G A T C C A A G T T

Transcription

RNA strand

G U A A G C U A G G U U C A A

Amino acid sequence

Val Ser STOP


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The Genetic CodeThere are 64 different tRNAmolecules.Each carries only 1 amino acid. (Why

64? What else are there 64 of?)Each has a unique anticodon on its

mRNA-binding end

anticodon is complementary to thecodon on the mRNA.

Another case of

complementary base

pairing


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Transcription

Translation

1. Identify the

DNA

nucleus mRNA

tRNA

Codons

Anticodons

Ribosome

Amino acids

2. Identify 2 instances

of complementary

base pairing


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1

2

3

4?


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mRNA Processing

mG (methyl-guanine) cap is addedto starting end.Helps mRNA attach to ribosome

Splicing occurs to remove non-codingsegments called introns. Remaining,coding segments are exons.

String of adenines added to the

other end (a poly-A tail)Protect the mRNA from being broken

down.


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mRNA Processing


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Review

DNA _____ _____ traitDNA is made of building blocks called

_____. How many different building

blocks?The is composed of sequences of ___

nitrogenous bases called _____

that code for a specific amino acids.

There are ____ different codons.

There are _____ different amino acids.


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Review

Transcription occurs in the ______.

Translation occurs in the ____.

How many different tRNA molecules are

there?

What is a codon?


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How Do Prokaryotes Do It?

Prokaryotes have 1circular gene.90% translated, few

introns.Additional genes may

be found on plasmids,smaller DNA circles.Plasmids can be

transferred betweenbacteria for a type ofsexual reproduction.


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How Do Viruses Do It?

Must use host cells geneexpression machinery. Viral

genetic info can be DNA or RNA.


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Mutations

Changes in the genetic material

including

DNA base sequencesstructure of a chromosome


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DNA MutationsPoint Mutations

N-base substitutionsUsually change a single

amino acid in a proteinSilent mutations base

change w/o amino acidchange

Frameshift Mutations Insertions or DeletionsUsually alter all the amino

acids in the protein fromthe site of the mutation.


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Chromosomal Mutations

Changes to the chromosomal structureusually due to breakage during celldivisionDeletion a section is lost or deletedDuplication a section is repeated Inversion a section is broken out and then

spliced back in incorrectlyTranslocation a section of one chromosome

attaches to a different chromosome


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Chromosomal MutationsLE 15 -14

Deletion

Duplication

Inversion

Reciprocaltranslocation

A deletion removes a chromosomalsegment.

A duplication repeats a segment.

An inversion reverses a segment

within a chromosome.

A translocation moves a segment

from one chromosome to another,nonhomologous one.


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Mutations and Human

DiseaseMutations may result in proteins that do notfunction properly.Metabolic diseases - enzymes are nonfunctional thus

interfering with normal metabolismTay Sachs

Transport diseases transport proteins are missing ornonfunctional interfering with cellular transport Cystic Fibrosis

Structural disease structural proteins are abnormal thus

interfering with normal growth and development. Sickle Cell Anemia


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Somatic cell vs. Sex cell

mutationsSomatic cell mutation affects only

one cell

Not inheritedMutation of tumor suppressor genes

in somatic cells may lead to cancer.

Mutations in sex cells are inherited andwill be found in all cells of the offspring.


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DNA Technology

DNA Extraction - the opening of cellsto separate/isolate DNA from other

cell partsDetergent

Meat tenderizer

Cold ethanol


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DNA Technology:

Copying DNAPolymerase chain reaction_(PCR)makes many copies of a small amount of

DNA

Tests requiring large DNA samples can nowbe run

DNA Technology:


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DNA Technology:

Cutting DNA

Large DNA molecules are cut intofragments by restriction enzymes.Found in bacteria, used for defense

These enzymes recognize and cutDNA at specific sequences.

DNA T h l


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DNA Technology:

Separating DNADNA fragments can be separated

and analyzed using gelelectrophoresis

Allows scientists to comparedifferent DNA samples


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Meiosis

Recall mitosis: cell of somatic (body) cells.Results in diploid daughters; clones of parent.

Meiosis: cell that forms haploid gametes.

Why is meiosis important?Sexual reproduction

Genetic variation among offspring


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Meiosis

3 Differences between mitosis andmeiosis:Cell divides 2X, but only replicates

chromosomes 1X. Results in haploid cellsDistributes random mixture of parent

genes (Independent assortment)

Homologous chromosomes pair up during 1st

cell . Here, they often exchange genes

Crossing Over

Meiosis


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MeiosisTwo Divisions take place:

Meiosis I Separation of homologouschromosomes. P

1M

1A

1T

1

Meiosis II Separation of sister

chromatids. (Same as mitosis) P2

M2

A2

T2

Four haploid daughtercells.

Genetic variation!

A must for natural

selection

Stages of Meiosis 1


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Stages of Meiosis 1

tetrads

Stages of Meiosis 2


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Stages of Meiosis 2

Meiosis: Production of


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Meiosis: Production of

Gametes

Females produce 1 large cell, the

ovum. 3 small polar bodies

disintegrate.

Males produce 4 equal sized sperm


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Errors in MeiosisNondisjunction. Unequal

separation of chromosomesleads to a gamete that is +1or 1 chromosome. n +1 = trisomy

n 1 = monosomyOften, embryo dies

Ex: Downs syndrome, trisomy21 1/700 births, higher risk in moms

over 35.


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Errors in Meiosis

Translocation. Large parts of chromosomes

break off and switch places.

Ex: the Philadelphia chromosome results whenpart of chrom 9 and 22 exchange positions.

A gene promoter placed at the beginning ofras, a

protein-encoding gene that initiates cell

constant gene expression, protein always

produced. This protein activates the cell cycle.

Philadelphia chromosome leads to leukemia

(cancerous WBC).


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Karyotypes

May be used to check for fetal

abnormalities.

Chromosomes are stained to showbanding.

Stains only bind to specific regions.

ID chromosomes by size, centromerelocation, and banding.

Karyotypes


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Karyotypes


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Any Questions?

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