DNADeoxyribonucleic

Acid

• DNA is our genetic code.

• DNA is located in the nucleus of every living cell in our bodies.

• DNA is made up of smaller units called nucleotides.

• Nucleotides make segments on DNA called genes.

• Genes control traits that are inherited from parents.

Humans have 46 strands of DNA called

chromosomes or chromatin.

• Our chromosomes are arranged in 23 pairs.

• KARYOTYPE: Man-made arrangement of all chromosomes in a cell. (shown here)

We have over 30,000 functional genes located on our 46 chromosomes.

• For genes to express themselves as a trait, you need a gene pair.

• In each pair of chromosomes: 1 came from mom and 1 came from dad.

nucleotides DNA genes chromosomes

STRUCTURE OF A NUCLEOTIDE

• A nucleotide is the simplest monomer of a DNA molecule. It is composed of 3 parts:

1. A phosphate group

2. A deoxyribose sugar

3. A nitrogenous base

Nitrogenous Bases• Guanine = G

• Cytosine = C

• Adenine = A

• Thymine = T

• Uracil = U*

(*Replaces T in RNA only!)

Nitrogenous Bases

• C always pairs with G

• A always pairs with T**In RNA, A always pairs with U

• Bases are held together with hydrogen bonds

–A T (2 H bonds)

–C G (3 H bonds)

Chargaff’s Rules• Erwin Chargaff, American

biochemist

• The percentage of Guanine (G) and Cytosine (C) bases are almost equal in any DNA sample.

• The same is true for Adenine (A) and Thymine (T) bases.

Nitrogenous Bases

• Purines—

2 rings (A & G)

• Pyridimines—

1 ring (C & T)

THE DISCOVERY OF DNA

BACK THEN…

IT WAS A RACE!

JAMES WATSON & FRANCIS CRICK

• February 28, 1953

• Watson was only 25 years old!

• Crick was 37 years old

MAURICE WILKINS &ROSALIND FRANKLIN

• In 1962, Watson, Crick, and Wilkins were awarded the Nobel Prize for Physiology or Medicine

• "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material“

DNA vs. RNA

DNADeoxyribonucleic

acid

1. Double helix (larger in size)

RNARibonucleic acid

1. Single strand (smaller in size)

DNA2. Carries

instructions for genetic blueprint (directions for making proteins)

RNA2. Translates and

decodes genetic message and builds proteins

DNA3. Found in the

nucleus

4. Sugar = deoxyribose

RNA3. Found in the

nucleus, ribosomes, cytoplasm

4. Sugar = ribose

DNA5. Processes:

-replication

-transcription

6. 4 nitrogen bases

A, T, C, G

RNA5. Processes:

-transcription

-translation

6. 4 nitrogen bases

A, U, C, G

DNA7. One type

RNA7. Three types

-messenger-ribosomal-transfer

All made from DNAAll have different

structures to suit their functions

TYPES OF RNA

MESSENGER RNA

• Also called mRNA• Acts as a messenger (carries

genetic instructions)• Moves genetic instructions out

of nucleus after making a copy• (DNA can’t leave the nucleus!!!)

MESSENGER RNA

• Copy is carried to the ribosome to be translated

• Contains special base sequences called CODONS (a code word)

• CODON—Series of 3 bases

MESSENGER RNA• Shape of mRNA:

–Long, linear single strand

TRANSFER RNA

• Also called tRNA

• Two functions:

–Decoder/translator of genetic message

–Transports amino acids to ribosome for assemble of protein

TRANSFER RNA

• Has two important binding regions–ANTICODON: sequence of 3 bases

on tRNA that must be complementary of mRNA codon)

–Attachment site for AMINO ACID to bind

TRANSFER RNA• Shape of tRNA:

–Folded linear molecule, resembles a “t” shape or “cross”

RIBOSOMAL RNA

• Also called rRNA• Site where amino acids are

assembled into proteins needed by the cell

RIBOSOMAL RNA• Shape of rRNA:

–Makes up the structure of the ribosome