DNA

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DNADNA• locatedlocated in the

nucleus• Function:Function: Carry

genetic material

• Many People contributed to the discovery of DNA.

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People Who Discovered DNA

• 1928 – Frederick Griffith - DNA = carrier of genetic info

• 1944 – Avery – Genes = composed of DNA

• 1952 – Hershey and Chase – genetic material = DNA, not protein

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People Who Discovered DNA

• 1952 – Rosalind Franklin – DNA = twisted

• 1952 – Edwin Chargraff - #A = #T; #C = #G; Chargraff’s Rule

• 1953 – Watson and Crick – Discovered structure of DNA we know today

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Shape of Shape of DNADNA1.1.Double HelixDouble Helix..

--Twisted ladder or Twisted ladder or spiral staircasespiral staircase

2.2.Two strandedTwo stranded

3.3.Held together by Held together by hydrogen bondshydrogen bonds

4.4.Made of four Made of four NucleotidesNucleotides

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RememberRemember: :

• DNA is a nucleic acid.

• Nucleic acids are made of nucleotides 77

Structure of Structure of DNADNA

Nucleotides

• DNA = long chain of nucleotides

• 4 that make up DNA• Have 3 parts: a

sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base

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4 NitrogenousBases

• Adenine• Guanine• Cytosine• Thymine

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Sides of Sides of the the “Ladder” “Ladder” are made are made up of up of sugar sugar and and phosphatphosphate.e.

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AdenineAdenine alwaysalways pairs with pairs with ThymineThymine

CytosineCytosine alwaysalways pairs with pairs with GuanineGuanine

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Would Thymine be able to pair up with Guanine?NO!!

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DNA DNA ReplicationReplication

•Before mitosis, the DNA must be replicated (Copied) exactly.

•Each strand can be used to make the other strand.

•Many enzymes are involved.

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Chromosome Structure

• DNA is packed very tightly as chromosomes in the nucleus.

• Human nucleus has 1 meter of DNA!

• Smallest human chromosome has 30 million base pairs.

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ChromosomeStructure

• A chromosome has DNA and protein-chromatin.

• Tiny sections of DNA are called genes

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Steps:

1. parent/original strands are unwound with the help of DNA helicases (enzymes).

Replication Bubble

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Semi-conservative replication

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Steps:

2. DNA polymerase attached new nucleotides to the parent strands

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DNA replication website

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How a protein is How a protein is mademade

•TranscriptionTranscription•TranslationTranslation

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DNA codes for all of DNA codes for all of the cell proteins.the cell proteins.

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Overview: • DNA is located in the Nucleus• Proteins are made on the ribosomes.• DNA makes a copy (send a message) called “mRNA”

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Two Steps of Protein Synthesis1. Transcription 2. Translation

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Transcription• a copy of the DNA is made…the copy

is called messenger RNA or mRNA. • The mRNA takes the code to the

ribosome.

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DNA vs. RNA

• Double Stranded

• AGTC

• Deoxyribose

• NEVER!

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• Single Stranded

• AGUC

• Ribose

• YES!

DNA Transcription

• During transcription the DNA unzipped and RNA nucleotide are paired up with the DNA bases.

• Website

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•Once the mRNA copy is made, it can go to the ribosome to be translated.

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• Remember….Proteins are made out of amino acids.

• There are 20 different amino acids.

• 3 bases code for each amino acid = codon. 33

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How you figure out

which codon is coding for

which amino acid…

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•Once the mRNA gets to the ribosome, the protein can be assembled.

•Transfer RNA brings the amino acids to the ribosome.

• Website

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• The three letter code on the mRNA is called a codon.

• The three letter code on the tRNA that is matched up with the mRNA is called an anticodon.

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Review Clip

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Mutations

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Mutations•A sudden change in the genetic

code is called a mutation.•Most mutations have little or no

effect on the organism.•Mutations can be spontaneous or

may be caused by environmental factors called mutagens.

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Mutations in DNA usually occur through one of three

processes:1- DNA damage from environmental

agents such as ultraviolet light (sunshine) or nuclear radiation

Certain chemicals called mutagens2- Errors that occur when a cell

replicates its DNA in preparation for cell division.

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Types of Mutations

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Point mutation

-a simple change

in a single base of the gene sequence

- 3 Types: 1. Point

2. Insertion3. Deletion

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Frame-shift Frame-shift MutationsMutations

In a frame-shift mutation, one or more bases are deleted or inserted, the equivalent of

adding or removing

letters in a sentence.

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Original:

THE CAT ATE THE RAT

Deletion:

THE CAT ATE THE RAT

THE CTA TET HER AT

Insertion

THE CAT ATE THE RAT

THE CAT ATT ETH ERA T

Chromosomal Mutations

• Mutations can occur that involve whole or partial chromosomes– Non-disjunction – homologous chromosomes

don’t separate during meiosis – a gamete ends up with an extra chromosome (ex. Down’s syndrome)

– Crossing Over – parts of homologous chromosomes are swapped during meiosis

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Results of DNA Mutations

• The results of mutations can be The results of mutations can be • HelpfulHelpful

– They can result in a helpful trait such as They can result in a helpful trait such as better camoflagebetter camoflage

• NeutralNeutral– If the mutation does not cause a change If the mutation does not cause a change

in amino acid sequence, or the replaces in amino acid sequence, or the replaces 1 amino acid with one that is similar, 1 amino acid with one that is similar, the protein will still function the same. the protein will still function the same.

• HarmfulHarmful– A large change in the amino acid A large change in the amino acid

sequence can make a protein that does sequence can make a protein that does not function at all. not function at all.

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Which of the Which of the following is the following is the

correct base-pairing correct base-pairing rule for DNA?rule for DNA?

A A-U; C-GB A-G; T-CC A-T; G-CD A-C; T-G 46

DNA TECHNOLOGY

forensicsforensics

agricultu

re

agricultu

re

DNADNA fingerprintingfingerprinting

medicinemedicine

industryindustry

genetic recombinationgenetic recombination..

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DNA FingerprintingDetermining the sequence of bases in DNA for comparisonsHow they identify criminals and do paternity tests (i.e. “Who is my Baby’s Daddy?”)

How DNA Fingerprinting works:

• Scientist cut up DNA into pieces using enzymes

• Then load the pieces into a gel.

• Electricity is run through the gel.

• The pieces of DNA move to the other end of the gel.

• Smaller pieces move farther.

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Who doesn’t belong?

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Recombinant DNA

•is a form of artificial DNA where DNA combined that would not normally be combined. •They cut, splice together, and insert the modified DNA molecules from different species into bacteria or another type of cell that rapidly replicates and divides. •The cells copy the foreign DNA right along with their own DNA. •Example: goldfish have genes for fluorescent proteins that have been inserted

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•the manipulation of an organisms genes•applications in medicine and the environment, industry, and agriculture. •Sheep are used in the production of alpha-1 antitrypsin, which is used in the treatment of emphysema. •Goats are also producing the CFTR protein used in the treatment of cystic fibrosis.•Crops are being devised that have natural insect repellants

Genetic Engineering

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Genetic Engineering Example:

In the plant world, the buds of cotton plants are vulnerable to worm attacks. The buds of a modified cotton plant resist these worms, resulting in increased cotton production.These gene insertions are ecologically safer than pesticides. They affect only the targeted pest.

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Scientists today have developed Scientists today have developed genetically altered bacteria. genetically altered bacteria. Among them are strains of bacteria Among them are strains of bacteria that that

eat up oil spillseat up oil spillsmanufacture alcohol and other manufacture alcohol and other chemicalschemicalsprocess minerals. process minerals.

There is concern about possible risks There is concern about possible risks to the environment and the general to the environment and the general population as genetically engineered population as genetically engineered bacteria are introduced.bacteria are introduced.

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Cloning

• Occurs when the DNA from an adult is inserted into the fertilized egg of the organism.

• Results in an offspring that is genetically identical to the parent.

• The DNA in the egg must be removed before the new DNA is inserted.

• Has been used in animals and plants, hopes for the future to allow for the cloning of organs.

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