Peptide Bond Formation

Walk the DogmaRECALL: The 4 types of organic molecules…

CARBOHYDRATES

LIPIDS

PROTEINS (amino acid chains)

NUCLEIC ACIDS (DNA and RNA)

The CENTRAL DOGMA of CELL BIOLOGY

Remember: DNA contains the instructions that tells the cell how to make proteins

Protein Synthesis has 2 main phases:

• Transcription (DNA → RNA)

• Translation (RNA → Protein)

DNA vs. RNADNA

-Deoxyribose Sugar-Double-stranded- A binds to T

RNA

- Ribose Sugar- Single-stranded- A binds to U (Uracil)

Ribonucleic Acid (RNA)

Messenger RNA (mRNA)• Structure: Linear Single Strand • Function: Carries genetic info from the

DNA in the nucleus to the cytoplasm

Transfer RNA (tRNA)• Structure: Hairpin Loop• Function: Binds and carries specific amino acids

Ribosomal RNA (rRNA)• Structure: Globular• Function: Combines with proteins to form ribosomes

Ribonucleic Acid (RNA)

Protein Synthesis: TRANSCRIPTION

Transcription: the process by which genetic information is copied from DNA to RNA

• DNA double-strand “unzips” • RNA polymerase (an enzyme) binds to a

specific region on DNA called a promoter• RNA polymerase travels along the gene,

creating a chain of mRNA that is complementary to the strand of DNA

• RNA polymerase reaches the termination signal at the end of the gene & falls off the DNA strand

A specific segment on a strand of DNA, which encompasses the space between a promoter and a termination signal, that contains the instructions to make a single polypeptide

DEFINITION: GENE

Post-Transcriptional Modification• Occurs before translation can begin

• Introns are removed, exons are joined– Intron: Non-coding sections of a gene

– Exon: Region of a gene that does code for protein

• This process a.k.a. mRNA SPLICING

• Catalyzed by a spliceosome (RNA/protein complex)

Intron = “Intervening”

Exon = “Expressed”

Translation’s Triplet Code

REMEMBER : Through transcription, the cell has created a strand of mRNA• The next step is to translate that sequence of (4) nucleotides

(A, U, G, C) into a correlating sequence of (20) amino acids

• The genetic code of the mRNA is “read” by the ribosome 3 nucleotides at a time

• Each 3 consecutive nucleotides is called a CODON• Each codon codes for a specific amino acid

Protein Synthesis: TRANSLATION

• mRNA leaves the nucleus and travels into the cytoplasm• A ribosome finds and binds to mRNA’s START CODON• A free-floating, amino-acid-carrying tRNA bearing the

appropriate ANTICODON binds to the start codon• The amino acid detaches from its tRNA• The ribosome slides 3 nucleotides down the mRNA strand• (THE PROCESS NOW REPEATS ITSELF) A free-floating,

amino-acid-carrying tRNA bearing the appropriate anticodon delivers the next amino acid to the forming polypeptide

• The ribosome reaches the STOP CODON and falls off the mRNA, releasing the polypeptide (FINAL PRODUCT)