DNA: deoxyribonucleic acid

2Copyright Cmassengale

I. DNA Structure A. Nucleotide—the monomer for nucleic acids B. DNA nucleotides are made of 3 parts: 1.deoxyribose—a simple 5-carbon sugar 2. phosphate group—made of phosphorus and oxygen

3. nitrogen bases DNA’s nitrogen bases are: a. adenine (A) called b. guanine (G) purines c. cytosine (C) called d. thymine (T) pyrimidines

C. Base Pairs 1. Adenine pairs with thymine A=T 2. Cytosine pairs with guanine C G 3. Held by hydrogen bonds

D. Double helix structure is like a twisted ladder: 1. deoxyribose and phosphate- the sides (the backbone) 2. base pairs-the steps

A Nucleotide

E. People Important to Modern Genetics 1. Hershey and Chase discovered that DNA is the genetic material in Watson and Crick (and Rosalind Franklin) discovered the DNA double helix structure in 1953.

Franklin’s Photograph

F. The Genetic Code 1. The order of the nitrogen bases is the genetic code. 2. The code is different in each organism, making each unique.

II. DNA Replication A. Is the process that copies the DNA DNA synthesis B. Also called DNA synthesis C. Occurs in S-phase of interphase

Replication animation in detailReplication animation in detail—faster paced Replication animation--slower paced

D. Steps in DNA replication: 1. Helicase enzyme binds to DNA and causes it to unzip (breaks hydrogen bonds). This splits the bases apart! [ Exposed bases are highlighted in yellow.]

2. Free nucleotides (found in nucleus) bind to exposed bases, forming new strands. DNA polymerase binds the complementary nucleotides. 3. The parent (old) strands completely separate from each other, forming…

…two DNA molecules, each with one parent strand and one new strand.

III. RNA—ribonucleic acid A. RNA is a type of nucleic acid that is different from DNA in 3 ways: 1. RNA has ribose as its sugar. 2. RNA has uracil as a base instead of thymine. 3. RNA is only one strand.

B. There are also 3 main types of RNA: 1. messenger RNA (mRNA)—copies DNA code 2. ribosomal RNA (rRNA)—makes up ribosomes 3. transfer RNA (tRNA)—Each carries a specific amino acid to ribosome.

IV. What does the DNA code have to do with protein? A. DNA code is information for building proteins. -like a blueprint for building a house

B. There are 20 different amino acids—monomers for making proteins. C. 3 nitrogen bases in row=codon D. A codon represents one amino acid.

E. The order of bases in DNA determines the order of amino acids (A.A.’s) in a protein. Ex: page 303 TCG CAT GCT AGC ATA ←DNA ←mRNA ←A.A.’s

F. There are 64 different codons: *61 for amino acids *start codon—AUG (methionine) *3 stop codons—UAA, UAG, UGA (signal the end of a protein)

G. Names for the DNA Code: 1. triplet code—because the code is read in sets of 3 bases (codons) 2. universal code—because each codon represents the same amino acid in all organisms

V. RNA Transcription and Translation A. transcription + translation = protein synthesis Transcription B. Transcription—makes a mRNA copy of the DNA Why?

→RNA can leave the nucleus because it is smaller than DNA. C. Steps in Transcription 1. Helicase unzips DNA. 2. Free RNA nucleotides pair with complementary bases on one DNA strand. RNA polymerase bonds these nucleotides together.

3. When copying is finished, the mRNA breaks away. The DNA strands rejoin and are UNCHANGED. 4. The mRNA leaves the nucleus and goes into the cytoplasm to a ribosome. Ex: ACG TAA GCA CCC TAG ←DNA ←mRNA

Transcription

Another diagram of Transcription

D. Translation—puts amino acids together to build a protein 1. rRNA—makes up the ribosome; produces enzymes needed to bond amino acids together specific 2. tRNA—each brings a specific amino acid to the ribosome

E. Steps in Translation 1. mRNA attaches to ribosome. 2. A matching tRNA anticodon pairs with first mRNA codon, bringing the correct amino acid with it.

3. A tRNA anticodon will pair with the 2 nd codon on the mRNA, bringing a 2 nd amino acid with it. 4. A peptide bond forms between the two amino acids. 5. mRNA slides through ribosome. The 1 st tRNA leaves.

6. Steps 3-5 will be repeated with the next codons. 7. When a stop codon is reached, the amino acid chain (polypeptide) breaks away from ribosome. Protein synthesis video clip

Protein Structure

Central Dogma

Protein Synthesis--Link #1 Greatest Discoveries in GeneticsGreatest Discoveries in Genetics video

VI. Review of Processes A. Replication 1. product/purpose: 2 identical DNA molecules (for 2 new cells) 2. when it happens: S-phase of interphase (before cell division) 3. where: nucleus

B. Transcription 1. product: mRNA 2. purpose: takes DNA code to ribosome 3. when it happens: whenever a protein is needed 4. where: nucleus

C. Translation 1. product/purpose: makes a protein (also called polypeptide) 2. when it occurs: immediately after transcription 3. where: ribosome