2.3 - Replication, Transcription, Translation Flashcards
What is transcription?
The transfer of information from a DNA molecule to an RNA molecule; the construction of an mRNA molecule based on the sequence of bases in a section of a DNA molecule
- Turning DNA into a message using RNA (this occurs in the nucleus)
What is translation
The transfer of information from an RNA molecule to a polypeptide; the construction of a new polypeptide based on the sequence of bases in a mRNA molecule
- Protein synthesis (accomplished in a ribosome)
What is RNA polymerase?
The enzyme that performs transcription; it forms a polymer of RNA from free RNA nucleotides
What is a ribosome?
The site (organelle) in a cells where translation occurs
What is tRNA?
The intermediary between mRNA coded information and the amino acid building blocks of proteins.
- Transfer RNA = carries an amino acid for later protein synthesis
What is DNA replication?
DNA replication is when we make an identical copy of our gene recipe book
- Occurs during synthesis
** Exact copy of all As, Gs, Ts, and Cs
What is our greatest concern when making protein during DNA replication?
We want to keep our protein recipe book/instructions accurate and complete when we decide to divide our cells (mitosis) or make gametes (meiosis)
What occurs during DNA replcation?
DNA unzips and copies itself when genes need to be copied (Eg. Gametes). Starts at special sites – “origins of replication”. DNA replication goes in both directions away from origin site.
What enzyme is responsible for the “unzipping” of DNA?
DNA unzips because of helicase (think helix-ase = unwinding the double helix of DNA)
What enzyme is responsible for the replication of DNA?
DNA replicates because of DNA polymerase (think polymer-ase = building a new polymer/strand of DNA)
What enzyme is responsible for identifying the ‘starting point’ for DNA replication?
DNA replication begins at a primer which is created by primase (think primer-ase = making a primer/starting point)
- Primer is made of RNA nucleotides (U, A, G, C)
What enzyme is responsible for gluing DNA fragments together?
DNA fragments are glued together by ligase (there is no cutesy short form for this one lol)
- Gaps in new DNA strand are glued together with ligase
What is it called when DNA is pulled apart?
When DNA is pulled apart, it is called a replication bubble or an origin of replication
What does semi-conservative mean?
Semi-conservating means there is 1 parent strand (the original strand of DNA) and one new strand (the copied version of DNA)
T/F: Mistakes during the initial paring of template and completementary nucleotides are very common
False: Enzymes proofread DNA during replication and repair damage in existing DNA; errors occur at a rate of 1 in 10,000 base pairs
What happens if there is an incorrect pairing during DNA replication?
If there is an incorrect pairing, the enzyme removes the wrong nucleotide and then resumes synthesis.
What is the final error rate of DNA replication (after initial pairing phase)?
The final error rate is only one per billion nucleotides.
What are the 3 stages of transcription?
- Initiation
- Elongation
- Termination
What occurs during initiation?
- RNA Polymerase binds to a promoter/start point
- DNA unwinds
- RNA synthesis begins
- Promoter tells the polymerase to “sit down” and begin transcribing RNA
What occurs during elongation?
- Polymerase moves downstream
- DNA helix reforms
- RNA strand gets longer thanks to the addition of new/ complementary nucleotides (copies template strand)
** Keeps going until a termination sequence is reached
What occurs during termination?
- RNA transcript is released
- Polymerase detaches
- Termination signal tells polymerase to stop building
** 5’ cap and Poly(A) tail (aglets) put on the ends to protect recipe from degradation
What occurs during translation?
- mRNA joins with small ribosomal subunit
- tRNA “base pairs” with mRNA appropriate 3 bases (start code is always AUG - methonine)
- Large ribosomal subunit joins
- Elongation (codon recognition, peptide bonds form, tRNa translocates to the next codon down)
- Translation ends when a termination sequence is reached (UAA, UAG, UGA = stop)*
- Newly made protein is released
What is a codon?
A codon is a combination of 3 RNA nucleotides (A, C, G, U) used to code for amino acids
What is the codon dictionary?
The codon dictionary is a dictionary containing all the possible codon “words” (64 possible)
What do coden sentences start/end with?
- All sentences start with AUG (methanine)
- All sentences end at a “stop” codon (UAA, UAG, UGA)
What are the various forms of mutation?
- Silent mutation
- Missence mutation
- Frameshift mutation
- Nonsense mutation
What does silent mutation mean?
Silent mutation means your recipe book is screwed up and your letters have changed, but they code for the same amino acid, so everything is fine (you have no visible mutations)
What does missence mutation mean?
Missence mutation means your recipe book is screwed up and a single amino acid in the chain is the wrong one (most of the time, you die/aren’t even born; if you live, you have diseases/disorders)
- Cystic fibrosis, Sickle Cell, etc.
What does frameshift mutation mean?
Frameshift mutation means you have too many/too few nucleotideds in an amino acid, so the order is wrong for the rest of the line, resulting in ALL NEW amino acids from that point on (AUG-AGG-UG- see how this is bad?)
- ALS, Muscular Dystrophy, etc.
What does nonsense mutation mean?
Nonsense mutation means you have a premature stop codon, and the sequence stops too early
- PKU, BRCA1 breast cancer gene, etc.
