DNATHE GENETIC MATERIAL OF LIFE

UNIT 5 (CHAPTER 8 IN BOOK)

What is DNA?

• Deoxyribonucleic acid

• Molecule that stores genetic information in all organisms

• DNA is stored in the nucleus of your cells

Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom and a beetle!!!!

DNA stands for:D: DeoxyriboseN: NucleicA: Acid

DNA is too small to see, but under a microscope it looks like a twisted up ladder!

DNA Timeline

• 1866: Gregor Mendel—shows that organisms have 2 copies for each heritable trait

• 1952: Hershey & Chase—proved that DNA is the hereditary material for life

• 1952: First cloned animal—the tadpole

• 1953: Watson and Crick—proposed double helix model of DNA based on work of Rosalind Franklin

DNA Timeline Continued

• 1973: The first “recombinant DNA” experiments are successful—a portion of one organism’s DNA is inserted into another organism

• 1996: First adult mammal is cloned—Dolly the sheep in Scotland

• 2000: First cloned monkey be stem cell separation, 5 piglets cloned using same technique

8.2: STRUCTURE OF DNA

DNA Structure

• DNA is a long chain made up of units called nucleotides

• Each nucleotide has three parts:

– Phosphate group (one phosphorus/3 oxygens)

– Deoxyribose (ring-shaped sugar)

– Nitrogen-containing base

• There are only four types of nucleotides—based on what type of nitrogen base they have

Structure of Nucleotides

Phosphate group

Deoxyribose

Nitrogen Base: Adenine (A)

Guanine (G)

Cytosine (C)

Thymine (T)

• One molecule of DNA contains BILLIONS of nucleotides, even though there are only 4 types of nucleotides:

– Adenine (A)

– Guanine (G)

– Thymine (T)

– Cytosine(C)

• The letter refers to the DNA bases as well as the nucleotide

Base Pairing

• DNA is a double helix structure—this means that there are two strands of DNA that wind together like a twisted ladder

• The strands are bonded together at the bases based on base pairing rules:

– Adenine always bonds to thymine

– Guanine always bonds to cytosine

The bases always pair up in the same way

Adenine forms a bond with Thymine

and Cytosine bonds with Guanine

Adenine Thymine

Cytosine Guanine

PO4

PO4

PO4

PO4

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Pairing up

sugar-

phosphate

chain

bases

THE DOUBLE HELIX

Remember

DNA is like an Oreo

Phosphates + sugars = cookies

Bases = cream filling

The structure of DNA consists of two strands wrapped around each other in a double helix

Nucleotides linked together:

Certain Nitrogen bases always link together:

Adenine—Thymine

Cytosine—Guanine

C

TA

G

Hydrogen Bonds

Covalent

Bonds

• So if one strand is…:

• A T C G A T A G C T A

• What is the other strand based on base pairing rules?

• T A G C T A T C G A T

8.3: DNA REPLICATION

DNA Replication

• Before a cell divides, it must make a copyof its DNA so that the new cell will have a full set of DNA

• The steps of DNA Replication:

1. DNA is unwound

a) Done by breaking the Hydrogen bonds that hold the strands together

2. DNA polymerase adds nucleotides, according to base pair rules

3. The strand is proofread as nucleotides are added, and mistakes can be fixed if the wrong base was added

a) A mistake is called a mutation

4. DNA polymerase continues adding nucleotides until a STOP signal is reached

Parent Strand

A—T

C—G

T—A

C—G

G—C

A—T

A—T

T—A

C—G

G—C

Stop

Parent—Complement

A—

C—

T—

C—

G—

A—

A—

T—

C—

G—

Stop

Parent—Complement

—T

—G

—A

—G

—C

—T

—T

—A

—G

—C

Stop

+

Copies are made/attached

The strandsseparate

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The strands

separate

PO4

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Each strand builds up its partner by adding

the appropriate nucleotides

DNA Replicationin action

Review Questions

• You need your CPS responders for this!

Which of the following are a part of nucleotides?

A. deoxyribose

B. phosphates

C. Nitrogen bases

D. All of the above

[Default][MC Any][MC All]

Which of the following represent a correct pairing of bases?

A. Adenine with thymine

B. Adenine with guanine

C. Guanine with thymine

D. Thymine with cytosine

[Default][MC Any][MC All]

Thymine, guanine, and sertocine are all DNA bases.

A. True

B. False

DNA replication occurs

A. During cell division

B. Before cell division

C. anytime

[Default][MC Any][MC All]

Which is the correct sequence for the complement strand to: A G G C T T

A. C T T A G G

B. G A A T C C

C. T C C G A A

D. A G G C T T

[Default][MC Any][MC All]

8.4: TRANSCRIPTION

RNA

• RNA: ribonucleic acid

– Chain of nucleotides made of:

• Sugar

• Phosphate group

• Nitrogen-containing base

– It’s a temporary copy of DNA that is used and then destroyed

DNA vs. RNA

DNA• Its sugar is deoxyribose

• Bases are: Adenine, Thymine, Guanine, Cytosine

• Double strand of nucleotides

RNA• Its sugar is ribose (has

one extra oxygen)

• Bases are: Adenine, Uracil, Guanine, Cytosine (uracil pairs w/ adenine)

• Single strand of nucleotides

Both have a sugar, phosphate, & base

Transcription

• Copying a sequence of DNA to make a complementary strand of RNA

• This is catalyzed (allowed to happen) by RNA polymerase

Basic steps of Transcription in Eukaryotic Cells

1. DNA strands unwind

2. RNA polymerase copies one strand of DNA and creates a complementary strand of RNA nucleotides (known as mRNA)

3. Once the gene has been copied, mRNA detaches from DNA

4. mRNA moves out of the nucleus and into the cytoplasm

start site

nucleotides

transcription complex

DNA

RNA

Step 1

Step 2

Step 3

RNA copying

Transcipted RNA

• ACG ATA CCC TGA CGAGCGTTAGCTATCG

• UGC UAU GGG ACU

Types of RNA

• Three types of RNA are formed during transcription, they will be used in translation:

– Messenger RNA (mRNA)

– Ribosomal RNA (rRNA)

– Transfer RNA (tRNA)

8.5: TRANSLATION

Translation

• Process that converts (translates) mRNA into a protein—aka protein synthesis

• mRNA is a message that codes for a protein when it attaches to a ribosome in the cytoplasm of the cell

• Each combination of 3 nucleotides (known as a codon) on the mRNA codes for an amino acid—groups of amino acids become proteins in the cell

Transcription and Translation

DNA

RNA

Protein

Transcription

Translation

Steps of Translation

1. mRNA moves out of nucleus and to cytoplasm

2. mRNA attaches to ribosome

3. Transfer RNA (tRNA) decodes the mRNA into amino acids, which link together into proteins

4. Protein (chain of amino acids) detaches from ribosome and goes off to work in the cell

Genetic Code

• Code that matches codons in mRNA to amino acids on tRNAs :

– The mRNA is read 3 letters at a time (codon)

– Each CODON represents one specific Amino acid

• There are 64 possible 3 letter combinations BUT only 20 amino acids….

• SO, some Codons code for more than one amino acid

mRNAcodons(3 bases)

Amino acids Stop codon

– codes for the end of the mRNA (no amino acid added)

Different codons code for different amino acids!!!

Transcription Translation

DNA RNA Protein

Directions to make proteins are safely stored in the nucleus

Carries the directions to the cytoplasm

Work to keep the cell alive

Transcription vs. Translation Review

Transcription

• Process by which genetic information encoded in DNA is copied onto messenger RNA

• Occurs in the nucleus

• DNA mRNA

Translation

• Process by which information encoded in mRNA is used to assemble a protein at a ribosome

• Occurs on a Ribosome

• mRNA protein

8.7: MUTATIONS

Mutation

• Change in an organism’s DNA

• It’s a mistake made during replication or transcription

• Can be:

– Harmful: diseases, disorders or deformities

– Helpful: help the organism to survive

– Neutral: organism is unaffected

Passing on Mutations

• If a mutation occurs in a sperm or egg cell, the mutation is passed on to offspring

• If a mutation occurs in a body cell, it only affects the organism and is not passed on to offspring

Causes of Mutations

1. During DNA Replication:• Base-pairing mistakes can happen but most are

fixed

2. Exposure to powerful Chemicals:• Cigarette smoke, smokeless tobacco, exhaust from

burning petroleum fuels, pesticides, herbicides, alcohol, sawdust from CCA lumber, paints, mineral spirits & oils, asbestos, etc.

3. Exposure to powerful radiation:• Gamma Rays (nuclear fuel & bombs)

• X rays (at hospitals & dental offices)

• UV rays (from sunlight and tanning beds)