DNA and Replication(Deoxyribonucleic Acid)

Chromosomes and DNA

• Our genes are on our chromosomes.

• Chromosomes are in the nucleus and made up of a chemical called DNA.

What is DNA’s Function?

• DNA contains the instructions for making proteins

• Chemical code for every trait

• “Blueprint” of life

Located in the Nucleus

Why do we study DNA?

We study DNA for many reasons, e.g.,

• Medical benefits such as cures for diseases.

• (Gene Therapy)

• Better food crops.• ( GMO’s -Genetically Modified

Organisms).

• Crime Scene Identification

Genetic material of cells…• GENES – units of genetic material that CODES

FOR A SPECIFIC TRAIT

• Called NUCLEIC ACIDS (DNA & RNA)

• DNA is made up of repeating molecules called NUCLEOTIDES

Nucleic acids: Many nucleotides linked in a long chain

DNA NucleotideBasic structure of DNA is a sugar-phosphate

backbone with 4 variable nitrogenous bases. This structure is called a nucleotide.

P

PhosphateGroup

Nitrogenous base(A, G, C, or T)

O

C1C4

C3 C2

5

Sugar(deoxyribose)

N

S

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Four nitrogenous bases

• Cytosine C

• Thymine T

• Adenine A

• Guanine G

DNA has four different bases which are connected by hydrogen bonds

Chargaff’s Rule• Adenine (Purine) must pair with Thymine

(Pyrimidine)

• Guanine (Purine) must pair with Cytosine (Pyrimidine)

• Their amounts in a given DNA molecule will be about the same.

G CT A

Chargaff’s Rule• If there is 20% of Adenine of then there

must be 20% of Thymine

• Therefore, there must be 30% of Guanine and 30% of Cytosine

G CT A

Hydrogen Bonds

• Hydrogen bonds attach the base pairs to each other.– Adenine and Thymine have 2 hydrogen

bonds between them

– Guanine and Cytosine have 3 hydrogen bonds between them.

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The Shape of the Molecule• DNA is a very long

polymer.• The basic shape is

like a twisted ladder • This is called a

“double helix”.• With complementary

base pairs (A-T, C-G)

DNA Molecule

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Rosalind Franklin – Studied the structure of DNA USING X-Ray. She discovered that DNA is a helical structure.

X-ray photo of DNA.

Double Helix

Watson & Crick’s Model

Nobel Prize 1962

Watson and Crick – build the DNA molecule model from Franklin’s X-ray.

What is the correct complimentary DNA strand

for the following CGTAAGC?

A. GCATACG

B. GCATTCG

C. CCATTGC

D. CGATACG

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Which of the following codes for your traits?

A. Sugars

B. Nitrogen Bases

C. Phosphates

D. All of the above

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What is the building block of a nucleic acid?

A. Polymer

B. Lipid

C. Carbohydrate

D. Nucleotide

Vocabulary✓ Replication – the process of DNA duplication.

✓ Replication fork – Site where DNA strandsseparate and replication occurs.

✓ Enzyme – a protein that facilitates a specific chemicalreaction in the body.

✓ Helicase: Unzips

DNA strands

✓ DNA Polymerase: Joins

nucleotides back together. Also, has proofreading function. Detects incorrectly paired nucleotides and corrects them.

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Vocabulary✓ Leading strand (5’ to 3’) – DNA strand

that forms as a continuous strand during DNA replication.

✓ Lagging strand (3’ to 5’) – DNA strand that forms as a series of short segments, called Okazaki fragments, which are then connected together.

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What is DNA replication?

What is DNA replication?❑ Happens in the nucleus

❑ Happens during Interphase (S phase)

❑ During DNA replication, the DNA molecule produces two new complementary strands.

❑ Each strand of DNA serves as a template for the new strand.

❑ Described as semiconservative because each DNA molecule has one new strand and one original strand.

Steps of DNA Replication

1. The two original strands of DNA are separated by helicase at the replication fork

2. DNA Polymerase adds complimentary nucleotides to each strand

3. Two DNA molecules that areidentical to each other.

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DNA Replication--- transcription--- translation

Replication conserves genetic information

- Each parent or original strand of DNA serves as a template this means the genetic information stays the same or is conserved.

DNA Replication

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What did we learn?

What did we learned?

✓ DNA, the genetic material of organisms, is composedof four kinds of nucleotides.

✓ Each nucleotide consists of a sugar, a phosphate group and one of four bases.✓ Sugars and phosphates on the outside✓ Nitrogenous bases paired by hydrogen bonds

(A with T, C with G) ✓ The paired strands form a twisted-zipper

shape called a double helix.✓ Before cell division, DNA copies itself in a

process called replication.✓ During replication, DNA separates into two strands,

and produces two new complementary strands following the rules of base pairing.

What is the essential question?

How does replication ensure that identical copies of DNA are made?

Genetic Diversity…• Different

arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

The figure to the right shows which of the following?

a. Translation

b. Replication

c. Transcription

d. Protein Synthesis

Which choice describes DNA after replication has taken place?

A. one molecule with two original strands and one molecule with two new strandsB. two molecules, each with one original and one new strandC. two molecules, each with two new strandsD. two molecules, each with two old strands

At what point in the cell cycle does DNA replication occur and why?

A. before a cell divides, to provide each of the two resulting cells with a complete set of DNA instructionsB. before a cell divides, to ensure that the DNA will fit into the resulting cellsC. during cell division, to ensure that the DNA will fit into the resulting cellsD. after a cell divides, to provide each of the two resulting cells with a complete set of DNA instructions.

Differences in DNA and RNA

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http://www.classzone.com/cz/books/bio_12_fl/resources/htmls/animated_biology/unit3/bio_ch08_0257_ab_protein.html

DNA Replication--- transcription--- translation

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• DNA is replicated in the nucleus.• DNA is transcribed into RNA in the

nucleus• RNA is translated to protein in the

cytoplasm

RNA types 1. Messenger RNA

(mRNA): copied from DNA, carriesinformation from chromosomes to ribosomes.

2. Ribosomal RNA (rRNA): make up ribosomes

3. Transfer RNA (tRNA): transportamino acids to ribosomes

• Look at the figure below: What structure does this figure show?

• A. DNAB. RNA

• C. Protein

• D Amino Acid

A. Cytoplasm B. NucleusC. Ribosome D. Cell Membrane