Mr. ColemanBiology

DNA

Why do we study DNADNA?

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

-its central importance to all life on Earth,

-medical benefits such as cures for diseases,

-better food crops.

DNADNA DNA is often called

the blueprint of life..

In simple terms, DNA contains the instructions for making proteins within the cell.

Chromosomes and DNAChromosomes and DNAProteins are made from the blueprint that genes provide.

Genes are on chromosomes in the cell’s nucleus.

Chromosomes are made up of a chemical called DNA.

The Shape of the MoleculeThe Shape of the Molecule

DNA is a very long polymer.

The basic shape is like a twisted ladder or zipper.

This is called a double helix.

In 1952 Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses that infect bacteria.

These viruses were made of only protein and DNA.

A Little History of the Quest to Find the Carrier of Our Genetic Heritage

Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope.

By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses.

In 1953, Rosalind Franklin first put forth the possibility of DNA having a double helixical shape. She based this on X-ray diffraction images of DNA crystals she had produced in the laboratory.

Also in 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases.

Watson and Crick proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.

Because DNA is composed of two strands twisted together, its shape is called double helix.

The Double Helix The Double Helix MoleculeMolecule

The DNA double helix has two strands twisted together.

One Strand of DNAOne Strand of DNA

The backbone of the molecule is alternating phosphate and deoxyribose, a sugar, parts.

The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

NucleotidesNucleotides

C C

C

OPhosphate

O

CC

O -P OO

O

O -P OO

O

O -P OO

O

One deoxyribose (or ribose) together with its phosphate and

base make a nucleotide.

Nitrogenous base

Ribose

One Strand of DNAOne Strand of DNA

One strand of DNA is a polymer of nucleotides.

One strand of DNA has many millions of nucleotides.

one nucleotide

Four nitrogenous basesFour nitrogenous bases

• Cytosine C• Thymine T

• Adenine A

• Guanine G

DNA has four different bases:

Two Kinds of Bases in DNA

• Pyrimidines are Pyrimidines are single ring bases.single ring bases.

• Purines are double Purines are double ring bases.ring bases.

Thymine and Cytosine are Thymine and Cytosine are pyrimidinespyrimidines

Thymine and cytosine each have one Thymine and cytosine each have one ring of carbon and nitrogen atoms.ring of carbon and nitrogen atoms.

Adenine and Guanine are Adenine and Guanine are purinespurines

AdenineAdenine and and guanineguanine each have two each have two rings of carbon and nitrogen atoms.rings of carbon and nitrogen atoms.

Two Stranded DNATwo Stranded DNA

Remember, DNA has two strands that fit together something like a zipper.

The teeth are the nitrogenous bases but why do they stick together?

Hydrogen BondsHydrogen Bonds

The bases attract each other because of hydrogen bonds.

Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

Hydrogen BondsHydrogen Bonds

When making hydrogen bonds,

cytosine always pairs up with guanine and adenine always pairs up with thymine.

Important:Important:

Adenine and Thymine always join together

A T

Cytosine and Guanine always join together

C G

DNA by the numbersDNA by the numbers• Each cell has about 2 m

of DNA.• The average human has

75 trillion cells.• The average human has

enough DNA to go from the earth to the sun more than 400 times.

• DNA has a diameter of only 0.000000002 m.

The earth is 150 billion mor 93 million miles from the sun.

1) In the Hershey Chase Experiment, DNA was labeled with __________, and bacteriophage (virus) protein was labeled with ____________.

A. radioactive phosphorous, radioactive sulfur B. radioactive sulfur, radioactive phosphorous C. codons, anticodons D. DNA Polymerase, RNA polymerase

2) In the ladder analogy of the DNA molecule, the "rungs" of the ladder are: A. sugars B. phosphates C. paired nitrogenous bases D. joined sugar and phosphate

3) Which of the following best describes the arrangement of the sides of the DNA molecule? A. twisted B. antiparallel C. bonded D. alternating

4) If a DNA molecule is found to be composed of 40% thymine, what percentage of guanine would be expected. A. 10% B. 20% C. 40% D. 80%

5) A nucleotide consists of: A. a phosphate and a base B. a phosphate, and a sugar C. a base and an amino acid D. a phosphate, a sugar, and a base

6) The sugar in RNA is _____, the sugar in DNA is _______ A. deoxyribose, ribose B. ribose, deoxyribose C. ribose, phosphate D. ribose, uracil

7) Which of the following is found in RNA but not DNA? A. uracil B. deoxyribose C. phosphate D. adenine

8) DNA is a polymer of:

A. nucleosides B. fatty acids C. deoxyribose sugars connected by phosphodiester

bonds D. nucleotides

• 9) Which of the following are pyrimidines?

A. adenine and cytosine B. adenine and guanine C. cytosine and guanine

D. cytosine and thymine

10) Which of the following are purines?

A. adenine and cytosine B. adenine and guanine C. cytosine and guanine D. cytosine and thymine

11) A nucleic acid was analyzed and found to contain 32 percent A, 18 percent G, 17 percent C, and 33 percent T. The nucleic acid must be

A. single-stranded RNA B. single-stranded DNA C. double-stranded RNA D. double-stranded DNA

12) What does DNA stand for?

A. Design of Natural Animals

B. Deoxyribonucleic acid

C. Doneoribonucleic acid

D. None of the above

13) Where in a cell is DNA located at?

A. Cytoplasm

B. Food vacuole

C. Nucleus

D. Cell membrane

14) DNA’s function in the cell is …

A. The instructions to the make-up to a living

organism.

B. To control what goes in and out of an organism.

C. To take over the mind as a back-up.

D. To give dreams and ideas in the mind.

15) The building blocks of DNA are called ……

A. Legos

B. Electrons

C. Neoculiotis

D. Nucleotides

16) The four DNA building blocks are …

A. Guanine, Adenine, Riginine, Jynine

B. Guanine, Adenine, Cynine, Thymine

C. Guanine, Adenine, Cytosine, Uracil

D. Guanine, Adenine, Cytosine, Thymine

17) A nucleic acid was analyzed and found to contain 37 percent A, 16 percent G, 22 percent C, and 25 percent U. The nucleic acid must be:

A. single-stranded RNA B. single-stranded DNA C. double-stranded RNA D. double-stranded DNA

18) A nucleotide consists of A. a sugar, a protein, and adenine B. a sugar, an amino acid, and a starch C. a sugar, a phosphate group, and a nitrogen- containing base D. a starch, a phosphate group, and a nitrogen- containing base

19) The part of the molecule for which deoxyribonucleic acid is named is the

A. phosphate group

B. sugar

C. nitrogen base

D. none of the above

20) Who are the three people connected with the discovery of the shape of DNA?

A. Franklin, Watson, and Creap

B. Franklin, Watson, and Crick

C. Francis, Watson and Crick

D. Francis, Watson, and Creap