Nucleic Acids

Lab Biology- Chapter 10Honors Biology- Chapter 9

Found on chromosomes Segment of DNA Codes for a trait

Gene

Characteristic due to a single gene or multiple genes

Eye color

Hair color

Blood type

What is a trait?

Deoxyribose sugar

Phosphate group

Nitrogen containing base◦ Four possible bases

Structure of DNA

2 rings of carbon and nitrogen

Adenine

Guanine

Purines

1 ring of carbon and nitrogen atoms

Thymine

Cytosine

Pyrimidines

DNA is composed of 2 nucleotide chains

Nucleotides connected through covalent bonds

The Double Helix

Each strand has a 5’ and a 3’ end

Each strand runs in an opposite (antiparallel) direction

Antiparallel

Nucleotide linkage

Covalent bonds

between sugar

and phosphate

molecules

Forms a sugar-

phosphate

backbone

Honors

5’

3’

Covalent bond Chemical bonding through sharing of

electron pairs

Honors

Purine Pyrimidine A T – 2 Hydrogen bonds C G – 3 Hydrogen bonds

Complementary Base Pairing

Hydrogen bonding between base pairs Hydrogen atom - electronegative atom

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Hydrogen bonds? Covalent bonds?

Chargaff’s rule The DNA of any given species contains

◦adenine = thymine ◦guanine = cytosine

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Wilkins and Franklin Used X-ray diffraction

◦ A picture of how X-rays bounced off a DNA molecule

Discovering the double helix model

FranklinWilkinsX-ray diffraction

X-Ray diffraction Used to determine arrangement of atoms

within a crystal structure Distance between dark spots- distance

between turns of the helix

Honors

Performed no physical experiments on DNA Spent a lot of time thinking about DNA Focused on creating a model that fit with

the data

Watson and Crick

Wilkins, Watson, and Crick received the Nobel Prize in 1962

Franklin died in 1958 and was not recognized

Nobel Prize cannot be awarded posthumously

Nobel Prize

Write a two paragraph reflection on Rosalind Franklin. ◦ One paragraph should detail her contribution to

the discovery of the structure of DNA. ◦ Second paragraph should state your answer to

the questions: Do you think Franklin deserved the Nobel Prize? Why do you think she did not receive more

recognition? ◦ Evidence must be provided to support your

opinions. ◦ Complete this assignment on loose leaf paper.

Homework

Occurs in all living organism Takes place in the nucleus One double stranded

molecule two identical copies

DNA Replication

Original strand

New strand

Helicase (enzyme) holds the two strands

apart

◦ Break hydrogen bonds between bases

Step 1: Replication Fork

Replicates simultaneously

Honors

DNA polymerase synthesizes DNA by adding nucleotides in a 5’ 3’ direction

Leading strand- continuous◦ Moves in the direction of unwinding

Lagging strand- discontinuous

Step 2: DNA Polymerase

Lagging Strand Discontinuous Forms in the opposite direction of replication fork Creates Okazaki fragments Must wait for a new primer to be placed

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DNA Primase- lays down short segments of RNA primer

DNA Polymerase III- adds new nucleotides DNA ligase- bonds Okazaki fragments

together

Honors

Semiconservative model

Honors

What happens when DNA Polymerase makes a mistake?

Mutation- Change in nucleotide sequence

Can be repaired through DNA repair mechanisms

Mutations

One nucleotide is substituted for another Sickle Cell Anemia

Substitution

A nucleotide is deleted Cystic fibrosis

◦ Deletion of "AT" from the sequence "ATAT" in the CFTR gene

Causes a frameshift

Deletion

A nucleotide is added

Huntington’s disease

Causes a frameshift

Insertion

DNA segment is

broken and flipped

No frameshift

No loss of genetic

information

Different order

Hemophilia

Inversion

Part of the gene is moved◦ Either moved on the same chromosome or moved

to a different chromosome A form of Down syndrome Part of Chromosome 21 is moved to

Chromosome 14

Translocation

DNA Replication Game http://www.nobelprize.org/educational/medi

cine/dna_double_helix/dnahelix.html Honors: DNA Replication http://

www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html

DNA Replication: http://www.mcb.harvard.edu/losick/images/t

rombonefinald.swf

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