Protein Synthesis and Translation

Protein Synthesis - Translation Overview

• Genetic Code: Instructions for synthesizing proteins.

• Codon: Set of 3 nucleotides on mRNA.

• Amino Acid: Monomer for protein formation, linked by peptide bonds.

• Anticodon: Complementary 3 nucleotides on tRNA.

Purpose of Translation

• Goal: Interpret the mRNA instructions to create a polypeptide.

• Location: Occurs at ribosomes.

• Process:

  • Starts with mRNA.

  • Ends with a polypeptide.

Translation Steps

1. mRNA binds to the small subunit of the ribosome.

2. Ribosome reads mRNA codons in the 5' to 3' direction (1 codon = 3 RNA nucleotides).

3. tRNA molecules transport corresponding amino acids to the ribosome.

4. Ribosome forms peptide bonds between amino acids.

5. At the stop codon, ribosome releases the completed polypeptide chain.

Example

• DNA Sequence (template): 3' ext{TAC} ext{CTA} ext{TAC} ext{GAT} ext{T} 5'

• mRNA Sequence: 5' ext{AUG} ext{CUG} ext{AUG} ext{CUA} 3'

• Codons: AUG CUG AUG CUA

• Amino Acids: Met, Arg, Ser, Cys, Stop

Comparison of Genetic Processes

Protein Synthesis - Translation Overview

• Genetic Code: Instructions for synthesizing proteins.

• Codon: Set of 3 nucleotides on mRNA.

• Amino Acid: Monomer for protein formation, linked by peptide bonds.

• Anticodon: Complementary 3 nucleotides on tRNA.

  • Example Sequences: UAC, GCU, AGU, ACG, AUU

Purpose of Translation

• Goal: Interpret the mRNA instructions to create a polypeptide.

• Location: Occurs at ribosomes.

• Process:

  • Starts with mRNA.

  • Ends with a polypeptide.

Translation Steps

1. mRNA binds to the small subunit of the ribosome.

2. Ribosome reads mRNA codons in the 5' to 3' direction (1 codon = 3 RNA nucleotides).

3. tRNA molecules transport corresponding amino acids to the ribosome.

4. Ribosome forms peptide bonds between amino acids.

5. At the stop codon, ribosome releases the completed polypeptide chain.

Gene Regulation

• Gene expression is a highly regulated process.

• Turning genes "on" and "off" is critical for cell differentiation.

• Regulation can occur before, during, or after transcription or translation.

• Transcription Factors: Regulatory proteins that control gene activity.

  • Repressors: Decrease transcription.

  • Activators: Increase transcription.

• HIV is an example of a virus that disrupts regulation.

Epigenetics

• The study of changes in gene expression that are heritable.

• Different from mutations:

  • Mutation: A change in a DNA sequence.

  • Epigenetics: Does not affect the actual DNA sequence, just how that sequence gets expressed.

Example

• DNA Sequence (template): 3' \text{TAC CTA TAC GAT T} 5'

• mRNA Sequence: 5' \text{AUG CUG AUG CUA} 3'

• Codons: AUG CUG AUG CUA

• Amino Acids: Met, Arg, Ser, Cys, Stop

Protein Synthesis Overview

• Protein Synthesis: The process of reading the instructions in DNA to make a polypeptide.

• Polypeptide: A chain of amino acids; can bind to others and fold into a protein.

Central Dogma of Genetics

• DNA: Stores instructions and is located in the nucleus (which it cannot leave).

• Proteins: These are made in the ribosomes.

• Two Steps of Protein Synthesis:

  1. Transcription

  2. Translation

• Flow of Information: \text{DNA} \xrightarrow{\text{Transcription}} \text{RNA} \xrightarrow{\text{Translation}} \text{Protein}

3 Essential Types of RNA

• mRNA (messenger): Copies instructions in DNA and carries these to the ribosomes in the cytoplasm.

• tRNA (transfer): Binds and carries specific amino acids to the ribosome.

• rRNA (ribosomal): Along with proteins, these make up the ribosome.

  • They also help catalyze the formation of peptide bonds!

Transcription

• Process: \text{DNA} \rightarrow \text{mRNA}

• Purpose: To carry the code/instructions out of the nucleus. DNA never leaves the nucleus, but proteins are made in the cytoplasm by ribosomes.

• Location: Nucleus

• Starts with: DNA

• Ends with: mRNA

Comparison of Genetic Processes

Protein Synthesis - Translation Overview

• Genetic Code: Instructions for synthesizing proteins.

• Codon: Set of 3 nucleotides on mRNA.

• Amino Acid: Monomer for protein formation, linked by peptide bonds.

• Anticodon: Complementary 3 nucleotides on tRNA.

  • Example Sequences: UAC, GCU, AGU, ACG, AUU

Purpose of Translation

• Goal: Interpret the mRNA instructions to create a polypeptide.

• Location: Occurs at ribosomes.

• Process:

  • Starts with mRNA.

  • Ends with a polypeptide.

Translation Steps

1. mRNA binds to the small subunit of the ribosome.

2. Ribosome reads mRNA codons in the 5' to 3' direction (1 codon = 3 RNA nucleotides).

3. tRNA molecules transport corresponding amino acids to the ribosome.

4. Ribosome forms peptide bonds between amino acids.

5. At the stop codon, ribosome releases the completed polypeptide chain.

Gene Regulation

• Gene expression is a highly regulated process.

• Turning genes "on" and "off" is critical for cell differentiation.

• Regulation can occur before, during, or after transcription or translation.

• Transcription Factors: Regulatory proteins that control gene activity.

  • Repressors: Decrease transcription.

  • Activators: Increase transcription.

• HIV is an example of a virus that disrupts regulation.

Epigenetics

• The study of changes in gene expression that are heritable.

• Different from mutations:

  • Mutation: A change in a DNA sequence.

  • Epigenetics: Does not affect the actual DNA sequence, just how that sequence gets expressed.

Sequence Example

• DNA Sequence (template): 3' \text{TAC CTA TAC GAT T} 5'

• mRNA Sequence: 5' \text{AUG CUG AUG CUA} 3'

• Codons: AUG CUG AUG CUA

• Amino Acids: Met, Arg, Ser, Cys, Stop

Protein Synthesis Overview

• Protein Synthesis: The process of reading the instructions in DNA to make a polypeptide (a chain of amino acids).

• Central Dogma of Genetics:

  • DNA stores instructions in the nucleus.

  • Proteins are produced at the ribosomes in the cytoplasm.

  • Flow of Information: \text{DNA} \xrightarrow{\text{Transcription}} \text{RNA} \xrightarrow{\text{Translation}} \text{Protein}

Essential Types of RNA

• mRNA (messenger): Copies instructions from DNA and carries them to the ribosomes.

• tRNA (transfer): Binds and carries specific amino acids to the ribosome.

• rRNA (ribosomal): Along with proteins, these make up the ribosome and catalyze peptide bond formation.

Transcription

• Purpose: To carry the code/instructions out of the nucleus. DNA never leaves, but proteins are made by ribosomes in the cytoplasm.

• Location: Nucleus

• Direction: RNA is synthesized in the 5' \to 3' direction; the DNA template is read 3' \to 5'.

• Steps of Transcription:

  1. RNA Polymerase binds to the DNA promoter where transcription is to begin and unzips the gene that needs to be copied.

  2. RNA Polymerase uses complementary base-pairing rules (e.g., A-U, G-C) to match RNA nucleotides with the exposed DNA nucleotides.

  3. The completed mRNA molecule is released.

  4. DNA zips back up, and the mRNA leaves the nucleus to enter the cytoplasm.

Post-Transcription (RNA Processing)

• RNA Splicing:

  • mRNA contains introns (non-coding regions) and exons (coding regions).

  • This process removes introns and splices exons together.

  • Allows for multiple polypeptides to be made from a single gene through different exon combinations.

  • Mnemonic: Introns are in the way; Exons are expressed.

• 5' Cap (Modified G): Added to the 5' end to facilitate ribosome binding.

• Poly-A Tail (50-250 A's): Added to the 3' end to help the mRNA molecule exit the nucleus.

Translation

• Purpose: Interpret the mRNA instructions to create a polypeptide chain.

• Location: Ribosomes

• Steps of Translation:

  1. mRNA binds to the small subunit of the ribosome.

  2. Ribosome reads mRNA codons in the 5' to 3' direction (1 codon = 3 nucleotides).

  3. tRNA molecules transport corresponding amino acids to the ribosome based on the anticodon.

  4. Ribosome forms peptide bonds between amino acids to build the chain.

  5. At the stop codon, the ribosome releases the completed polypeptide chain.

Gene Regulation and Epigenetics

• Gene Regulation: Turning genes "on" or "off" to control cell differentiation.

• Transcription Factors: Regulatory proteins like repressors (decrease transcription) and activators (increase transcription).

• Epigenetics: The study of heritable changes in gene expression that do not change the actual DNA sequence.

  • Mutation: A change in the DNA sequence.

  • Epigenetics: A change in how that sequence is expressed.

Sequence Example

• DNA Sequence (template): 3' \text{ TAC GCT AGT ACG ATT } 5'

• mRNA Sequence: 5' \text{ AUG CGA UCA UGC UAA } 3'

• Codons: AUG - CGA - UCA - UGC - UAA

• Amino Acids: Met - Arg - Ser - Cys - Stop

Comparison of Genetic Processes