Lesson #12 Transcription

• What are the two main processes involved in gene expression?

  Transcription and translation

  
• What is the role of a gene?

  A gene is a nucleotide sequence that codes for RNA or protein

  
• What percentage of human DNA encodes functional molecules?

  1. 2%
• What are the types of RNA and their functions?

  • mRNA: codes for proteins
  • rRNA: components of ribosome, catalyze protein synthesis
  • tRNA: adaptors between mRNA and amino acids
  • snRNA: involved in pre-mRNA splicing
  • miRNA: regulates gene expression
• What is the function of RNA polymerase?

  It catalyzes the formation of phosphodiester bonds during RNA synthesis

  
• In which direction does RNA polymerase synthesize RNA?

  5’ to 3’ direction

  
• What is required for RNA polymerase to initiate transcription?

  It must be positioned on a promoter sequence upstream of the gene

  
• What happens during the termination of transcription?

  The RNA base pairs with itself to create a hairpin structure

  
• Where does eukaryotic transcription occur?

  In the nucleus
• How many different RNA polymerases are present in eukaryotes?

  Three different RNA polymerases
• What is the role of transcription factors in eukaryotic transcription?

  They recruit and activate RNA polymerase II

  
• What modifications occur to primary transcripts in eukaryotes?

  They receive a 5’ cap, a 3’ poly-A tail, and have introns removed
• What is the function of the 5’ cap on mRNA?

  It protects mRNA from degradation and helps align it for translation

  
• What is the role of spliceosomes in mRNA processing?

  They remove introns and splice together exons
• What is alternative splicing and its significance?

  • A single primary transcript can be spliced into different mRNAs
  • Allows for the production of different proteins from a single gene
  • Example: 20,000 genes can encode > 80,000 different mRNAs
• What is the process of translation?

  It converts RNA sequence into a polypeptide sequence

  
• What are the three stages of translation?

  Initiation, elongation, and termination

  
• How is the mRNA sequence read during translation?

  It is read in the 5’ to 3’ direction

  
• What distinguishes prokaryotic mRNA from eukaryotic mRNA?

  Prokaryotic mRNA often contains multiple coding sequences

  
• What is a codon?

  A codon is a sequence of 3 nucleotides that specifies an amino acid

  
• How many possible codons are there?

  64 possible codons
• What is the significance of the redundancy in the genetic code?

  It means that multiple codons can encode the same amino acid

  
• What is the structure of tRNA?

  tRNA is a single-stranded RNA that self-folds into a cloverleaf shape
• What is the role of aminoacyl tRNA synthetase?

  It loads amino acids onto the 3’ acceptor end of tRNA
• How do tRNA and mRNA pair during translation?

  The anticodon loop of tRNA recognizes and binds to the complementary codon in mRNA

  
• What is the wobble hypothesis in tRNA pairing?

  It allows some tRNAs to recognize more than one codon due to less stringent base pairing

  
• What are the components and functions of the ribosome?

  • Consists of two subunits: small (decodes mRNA) and large (catalyzes peptide bond formation)
  • Has three tRNA binding sites: E-site (exit), P-site (peptidyl), A-site (aminoacyl)

  
• What is the initiation process of translation in prokaryotes?

  The small subunit binds to the Ribosome Binding Site on mRNA to determine the start site

  
• How does initiation of translation differ in eukaryotes compared to prokaryotes?

  Eukaryotes bind to the 5’ cap to determine the start site

  
• What triggers the termination of translation?

  A release factor recognizes the stop codon and triggers the release of the polypeptide

  
• How do mutations affect gene and protein sequences?

  Mutations can alter the DNA sequence, leading to changes in the protein produced
• What are the types of point mutations and their effects?

  1. Silent Mutation: no change in amino acid
  2. Missense Mutation: changes encoded amino acid
  3. Nonsense Mutation: leads to a stop codon
• What is a frameshift mutation?

  It is an insertion or deletion mutation that changes the downstream reading frame
• What are the types of chromosomal mutations?

  • Deletion: part of chromosome is lost
  • Duplication: part of chromosome is copied
  • Inversion: part of chromosome is in reverse order
  • Translocation: part of one chromosome is moved to another chromosome

  
• How do mutations contribute to evolution?

  Mutations provide genetic variation, which is essential for evolution
• What is the balance that must exist in evolution regarding mutations?

  There must be a balance between new variation and the health of the species