peptide bond formation walk the dogma recall: the 4 types of organic molecules… carbohydrates...
TRANSCRIPT
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)