Both are nucleic acids…Be able to compare these two nucleic acids

DNA Monomer: Nucleotide

• 1 phosphate group• 1 deoxyribose 5-carbon sugar• 1 nitrogen-containing base (A, C, G, or T)

DNA polynucleotide• Alternating sugar and phosphate molecules

form backbone• Nitrogenous bases form complementary pairs

joined by hydrogen bonds• Adenine (A) pairs with Thymine (T)• Cytosine (C) pairs with Guanine (G)

DNA Bases

RNA Nucleotides• 1 phosphate group• 1 ribose sugar• 1 nitrogenous base

(A, C, G, or U)• Uracil replaces

thymine in RNA

Information Flow• Genetic information in DNA is transcribed to

RNA (transcription), then translated to protein (translation)

• The molecular basis of phenotypic traits are proteins that serve many different functions

Transcription & Translation

of

RNA Codons

One gene - One protein ?

• Each protein made at the ribosomes is controlled by a specific DNA gene (based on sequence of DNA base pairs)

• Changes in DNA base sequence can ultimately result in changes in the protein produced in cell

RNA Transcription

• DNA nucleotides are transcribed into RNA nucleotides in nucleus

• Adenine pairs with Uracil

• Cytosine pairs with Guanine

• Every 3 bases in DNA make 1 RNA triplet codon

RNA transcription• RNA polymerase allows DNA nucleotides to

be transcribed into RNA nucleotides and then links them together

• 3 different types of RNA are transcribed: 1. Messenger RNA (mRNA)

2. Transfer RNA (tRNA)

3. Ribosomal RNA (rRNA)

The Genetic Code

• 1961: The first RNA triplet codon was decoded and found to translate into a specific amino acid

• The genetic code is basically the same for all organisms, so bacterial cells can translate genetic messages from humans, and vice versa.

• Useful for Recombinant DNA technology

5’

3’

Transcription of a Gene

At the ends of each intron areSmall nuclear ribonucleoproteins or snRNP’s

And these recognize splice sites

Many snRNP’s join with protein = splicesome

Ribozymes = RNA’s that function as enzymes

Some intron RNA’s function as ribozymes to catalyze their own excision

Translation involves complex biochemistry!

…Correct matches between tRNA and aa (aminoacyl-tRNA synthetase)…Correct match between tRNA anticodon and the mRNA codon…Ribosomes facilitate the coupling of tRNA anticodons with mRNA codons during protein synthesis…rRNA has three binding sites for tRNA …….A site = holds the tRNA carrying the next amino acid to be added to the growing polypeptide …….P site = holds the tRNA carrying the growing poly- peptide chain …….E site = exiting tRNA

Transfer RNA

Transfer RNA

• Transfer RNA serve as “interpreters” during translation

• Each has an anticodon region that binds to specific codons on the messenger RNA

• Each also has an attachment site for an amino acid

E P A

5’

5’3’

3’

mRNA

APE

Initiation – mRNA, tRNA, aa2 rRNA subunitsRibosome scans downstream5’ 3’

Elongation – aa are added one by one to the precedingaa mRNA is moved thru theribosome in one directiononly..5’ end firstRibosome and mRNA moverelative to each other codonby codon

Termination – stop codonreaches the A site of ribosomeUAG, UAA, or UGA5’

3’A U G

U A C

EPA

E

E

E

E

P

P

P

P

A

A

A

Summary of transcription

and translation

E

E

E

Flow of genetic information

• DNA to RNA to protein• Polyribosomes = many ribosomes read one

mRNA• Post-transcriptional Modificaiton

– Coil and folding polypeptide

– Modify aa by adding a sugar, lipid or phosphate group

– Enzymes may remove one or more aa

– Enzymes may cut protein in ½

– Free ribosomes = proteins function and dissolve in cytosol

– Bound ribosomes = ER or Nuclear Membrane bound endomembrane system

RNA has many roles in a cell

Point MutationsSubstitutions

Insertions/DeletionsMutagens

What is a gene?

Sickle cell anemia: a single base mutation