Transcription and Translation, Mutation Quiz Flashcards
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The central dogma
Fundamental principle of molecular genetics
-States that genetic information flows from DNA→RNA→proteins
RNA Vs DNA
DNA:
Sugar: DNA contains deoxyribose, a sugar with one less oxygen atom than ribose.
Strands: DNA is typically double-stranded, forming a double helix.
Bases: The four nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). Adenine pairs with thymine, and cytosine pairs with guanine.
Shape: The double-stranded structure is stable and coiled into a double helix.
RNA:
Sugar: RNA contains ribose, a sugar with one more oxygen atom than deoxyribose.
Strands: RNA is usually single-stranded.
Bases: RNA uses adenine (A), uracil (U), cytosine (C), and guanine (G). In RNA, uracil replaces thymine as the complementary base to adenine.
Shape: RNA is typically single-stranded and can fold into various shapes, depending on its function.
- Function
DNA:
Genetic Material: DNA stores the genetic instructions used in the growth, development, functioning, and reproduction of all living organisms. It is the blueprint for all biological information.
Replication: DNA is replicated when cells divide, ensuring that each new cell receives an exact copy of the genetic information.
RNA:
Protein Synthesis: RNA plays a central role in protein synthesis.
Transcription - Initiation
initiation
Promoter region: a sequence of nucleotides in DNA that indicates where the RNA polymerase complex should bind to initiate transcription
-Key element of the promoter in eukaryotes is the TATA box (a portion of DNA with high percentage of Adenine and Thymine bases)
-Prokaryotes have a TATATT sequence instead for this
-RNA polymerase binds to a promoter region on the DNA same purpose
Transcription - Elongation
Elongation
RNA polymerase complex works its way along DNA molecule
-RNA polymerase, unlike DNA polymerase, can begin making the complementary copy without needing a primer to be already in place
-Synthesizes mRNA strand that is complementary to template strand of DNA
-T is replaced with U
-RNA polymerases work in the 5ʼ → 3ʼ direction, using the 3ʼ→ 5ʼ DNA strand as a template strand.
As RNA polymerase moves along the DNA, it unwinds the DNA at the forward end of the enzyme
-RNA strand grows as nucleotides are added, one by one forming a temporary RNA-DNA double helix with the template strand
-As the RNA polymerase passes, the DNA double helix reforms
-Once an RNA polymerase molecule has started transcription and progressed past the beginning of a gene, another molecule of RNA polymerase may start producing another RNA molecule if there is room at the promote
Transcription - Termination
The transcription is terminated when RNA polymerase recognizes a termination sequence.
Coding (sense) vs Template (anti-sense) strand
-Coding strand: the DNA strand that is not being copied but contains the same sequence as the new RNA molecule
-The template strand contains the sequence that is complementary to the sequence that is going to be transcribed
mRNA processing in eukaryotes (poly A tail, G cap, splicing of exons)
Poly(A) tail: a chain of adenine nucleotides added to the 3’ end of pre-mRNA molecule to protect it from enzymes in the cytosol
-Enables mRNA to be translated efficiently and protects from attack by RNA-digesting enzymes in the cytosol
The intron sequences are removed from pre-mRNA and exons are joined together to form mature mRNA
G Cap
-Involves covalent linkage of modified G nucleotides onto to 5’ end of pre-mRNA
-The cap is recognized by the protein synthesis machinery
-All eukaryotic mRNA undergo modifications on their ends
-These modifications convert precursors mRNA (pre-mRNA) to mature mRNA
Exons vs introns, alternate splicing
Exons are coding regions
Exons may be joined in different combinations to produce different mRNAs from a single DNA gene sequence
-A mechanism called alternative splicing increases number and variety of proteins encoded by a single gene
-Allows more than one possible polypeptide to be made from a single gene
-Alternative splicing helps understand why humans with only 20 000 genes can produce approx. 100 000 proteins
Structure tRNA
-3’ end of tRNA binds to specific amino acids
-Anticodon on tRNA complements mRNA codon
Structure of ribosome - a, p and e sites
-2 subunits: small and large
-E site → exit site
-P site → polypeptide binding site
-A site → amino acid site
-Composed of proteins and rRNA
-3 tRNA binding sites
Translation - Initiation
-mRNA, tRNA and small ribosomal subunit bind with P site at start codon
-Only the first tRNA binds to P at start codon
-Large subunit binds using energy from GTP
Translation - Elongation
mRNA read 3 nucleotides at a time in codons
-tRNA brings corresponding amino acid into the A site of the ribosome
-Ribosome catalyzes dehydration synthesis reaction between amino acids in P site and A site
-Peptide bond is formed
-Growing polypeptide now attached to tRNA in A site
-Ribosome moves forward one codon
-Free tRNA in P site exits out the back of ribosome on the E site
-tRNA (with polypeptide) moves into P site
Translation - Termination
-Elongation continues until reaching a stop codon
-There is no amino acid for stop codon, just STOP
-Release factor binds and hydrolyzes the bond between the last tRNA and its amino acid
-New protein is free
Frameshift Mutations
– shifts the reading frame of the codons so that a completely different amino acid sequence is produced from the point of the shift. Will likely not produce a functional protein
point mutations
– change in one nucleotide
○Substitution
○Substitutions will only affect a single codon
■THE FAT CAT ATE THE RAT
■THE FAT HAT ATE THE RAT
○Insertion (Frameshift)
■THE FAT CAT ATE THE RAT
■THE FAT CAT HATE THE RAT
○Deletion (Frameshift)
■THE FAT CAT ATE THE RAT
■THE FAT CAT AT THE RAT
