DNA STRUCTURE AND REPLICATION BUILDING BLOCKS OF DNA: Nucleotides:

1. 5 carbon sugar (deoxyribose) 2. Nitrogenous base (A, T, C, or G) 3. Phosphate group

NITROGENOUS BASESPYRIMIDINES PURINESSingle ring structure C and T Double ring structure G and A

Cytosine Guanine

Thymine Adenine

Molecular Genetics Bio 10 BCC Page 1 of 10

DNA STRUCTURE

Molecular Genetics Bio 10 BCC Page 2 of 10

Hydrogen bonds

C and G H bonds between 3 −

A and T H bonds between 2 −

hold bases togetherHydrogen bonds −C – G −A – T −Purine – pyrimidine − bases 2 −

Rungs of ladder phosphate groups of alternating sugar & Sides of ladder consist Twisted ladder Double stranded Double helix

One strand 5’ at top & 3’ at bottom ANTIPARALLEL STRANDS Other strand: 5’ at bottom & 3’ at top

Molecular Genetics Bio 10 BCC Page 3 of 10

Nucleotide

deoxyribose carbon in rd3

’ end 3

deoxyribose carbon in th5

’ end 5

Molecular Genetics Bio 10 BCC Page 4 of 10

codonAnti-

specific • with codon on mRNA Anti-codon base pairs • ribosomes carries amino acid to • transfer RNA •

tRNA

acid Amino

Site of protein synthesis % protein 40

(rRNA)RNAibosomal 60% rlarge small

subunits2

Ribosomes

cytoplasm to ribosomes in DNA in nucleus proteins from making carries code for

bases = AUCGsugar = ribose

single stranded

messenger RNA mRNA

Transcription

Transcription

Transcription

Bases = ATCG • deoxyribose Sugar = •

Double stranded• DNA

YNTHESISSROTEIN P

GENETIC CODE 1 codon = 3 consecutive bases 1 codon codes for 1 amino acid (A.A.) There are 4 bases (A, T, C, G) Thus 43 (64) possible combinations of codons There are 20 amino acids Code is redundant (2 or more codons code for same amino acid) but not ambiguous (no codon codes for more than 1 amino acid)

PROTEIN SYNTHESIS – OVERVIEWCentral Dogma of Biology

Molecular Genetics Bio 10 BCC Page 5 of 10

Protein

build protein) uses codons in mRNA to (

Translation

Transcription

mRNA

DNA (Coding strand)

• base-pairs RNA nucleotides with exposed DNA bases

• stops when reaches terminator

RNA Processing

occurs in eukaryotic cells

• Introns removed • Exons linked • 5’ cap added • Poly-A tail added

Spliceosome • Cut out introns

Molecular Genetics Bio 10 BCC Page 6 of 10

separates DNA strands • binds to promoter (TATA box) •

RNA polymerase

grows in 5’ to 3’ direction

mRNA

DNA

RANSCRIPTION– TYNTHESIS SROTEIN P

’ cap 5

Poly-A tail

• Slice exons together • consist of protein and snRNPs

PROTEIN SYNTHESIS – TRANSLATION

Initiation

mRNA binds to

small

l

ribosomal subunit

Initiator tRNA base pairs with 1st codon (start codon) on mRNA 1st amino acid - methionine

Large ribosomal subunit binds to complex Initiator tRNA located at P site P site – peptidyl-tRNA binding site A site = Aminoacyl-tRNA binding site

Elongation

Molecular Genetics Bio 10 BCC Page 7 of 10

2nd tRNA base pairs with 2nd

codon on mRNA at A site

• Peptidyl transferase forms peptide bond between 1st and 2nd amino acids

• 1st tRNA exits • mRNA shifts position by 1

codon • 2nd tRNA now at P site • 3rd tRNA base pairs with 3rd

codon at A site • process continues until stop

codon reaches A site

Termination

• Stop codon (UGA, UAA, UAG) reaches A site

• Release factor binds to stop codon

• Polypeptide hydrolyzed from tRNA at P site

• Complex disassembles • mRNA can be used again

Molecular Genetics Bio 10 BCC Page 8 of 10

• Polypeptide released

GENETIC ENGINEERING

RECOMBINANT DNA

Molecular Genetics Bio 10 BCC Page 9 of 10

Molecular Genetics Bio 10 BCC Page 10 of 10

Molecular Genetics Bio 10 BCC Page 11 of 10