BIOL 226 FINAL Flashcards
What does snRNA do?
Involved in the splicing process when mRNA is formed
What does rRNA do?
combines with proteins to form ribosomes
Once in the cytoplasm, the mRNA binds to a ribosome, which is a large complex comprised of several ribosomal RNA (rRNA) and many proteins. The ribosome is the site of protein assembly. The bases of the nucleotides in the mRNA are read three at a time by the ribosome. Each of these base triplets is called a codon and specifies one amino acid.
What does tRNA do?
Brings amino acids to sites of mRNA during protein synthesis
a cloverleaf‑shaped molecule containing an anticodon complementary to an mRNA codon and is attached to an amino acid specific to the anticodon. The interaction between the codons in the mRNA and the complementary tRNA anticodons dictates the order that amino acids are delivered to the ribosome. Enzymes within the ribosome join the amino acids from the tRNAs to form the peptide chain. When at least three amino acids are linked, the chain is considered a polypeptide.
What does siRNA do?
eliminates the expression of an undesirable gene
What does mRNA do?
Coding - carries genetic information to ribosomes for protein synthesis
a linear sequence of ribonucleotides transcribed from DNA that carries instructions for protein production
What does miRNA do?
inhibits the translation of mRNA into proteins
What is common about the promoter in both pro and eukaryotes?
In both prokaryotes and eukaryotes, the promoter is located in the 5′ direction, upstream from the transcription start site.
What does the promoter often contain in eukaryotic transcription?
In eukaryotes, the promoter often contains a TATA box, which is where the TATA‑binding protein binds. The binding of the TATA‑binding protein is the first step in eukaryotic transcription. When the TATA‑binding protein binds, it is part of a larger transcription factor complex, which then attracts other general transcription factors and the RNA polymerase, together forming the preinitiation complex.
What does the promoter contain in prokaryotic transcription?
In prokaryotes, the promoter contains a −35 and −10 region upstream of the transcription start site, which is recognized by the RNA polymerase holoenzyme. The RNA polymerase holoenzyme is composed of five units that make up the core enzyme plus a sigma factor subunit. After the RNA polymerase holoenzyme binds to both the −35 and −10 regions, transcription is initiated at the start site.
What occurs in the first step of transcription - initiation?
initiation, during which an enzyme called RNA polymerase binds to the DNA template at a specialized sequence called a promoter.
Before RNA polymerase can bind to the promoter, transcription factors must first bind and prime the promoter region.
Once bound, RNA polymerase unwinds local regions of the DNA double helix which enables the genetic code to be copied.
What occurs in the second step of transcription - elongation?
Once the DNA is unwound and the nucleotides are exposed, the elongation step begins. RNA polymerase reads the DNA template strand and adds nucleotides to the 3’ end of the growing chain.
What occurs in the last step of transcription - termination?
RNA polymerase continues to transcribe the DNA until it encounters a sequence that signals the end of the gene.
RNA polymerase detaches from the DNA and the string of RNA bases is released as a single‑stranded transcript.
The newly formed RNA transcript, also known as messenger RNA, is ready to be translated into a protein.
Which strand is the template strand in transcription?
3’
What is transcription?
The process by which DNA is copied to RNA
What is translation?
The process of using RNA to produce proteins
What are the 8 brief steps of eukaryotic transcription?
RNA polymerase II binds to DNA promoter element
DNA is unzipped by RNA polymerase
Ribonucleotides align with complementary DNA nucleotides
RNA polymerase links triphosphate ribonucleotides together
Guanine cap added to 5’ end of mRNA
RNA polymerase released from DNA
Splicing and polyadenylation (polyA tail) events modify mRNA
Processed mRNA leaves the nucleus
What is a transcription factor?
A protein that binds to a specific DNA sequence to regulate transcription
Can bind either upstream or downstream,
Can activate - recruits RNA polymerase
Can inhibit - blocks RNA polymerase from binding
What is a polyA tail?
Sequence of adenine nucleotides added onto the end of premRNA, added onto 3’ end
Facilitates export of mature mRNA from nucleus and protects from degradation
Stabilizes the trailing end of mRNA
What is an intron?
noncoding segment of DNA that lies between coding regions, is removed from premRNA
What is an exon?
Coding portion of DNA that is present in mature mRNA
exons are eventually expressed by being translated into AA sequences
What is alternative splicing and why is it important in eukaryotic organisms?
Alternative splicing is done by the spliceosome where it splices in slightly different places
Produces related but distinct proteins called isoforms
It increases the variety of proteins that can be produced without altering the genome size
What is the purpose of the 5’ cap?
Assists mRNA in binding to the small ribosomal subunit
Assists in RNA splicing
What happens in the three phases of translation?
During initiation, the small subunit of the ribosome and the initiator tRNA bind to the mRNA. This complex, along with other proteins known as initiation factors, scans the beginning of the mRNA for the first start codon, AUG. The 5′ cap of the mRNA is important for ribosome binding and helps to ensure that ribosomes load before the first start codon. Once the start codon is recognized, the large ribosomal subunit binds to the small ribosomal subunit and translation can& begin.
During elongation, additional amino acids are added to the growing polypeptide chain. For each codon after the start codon, a tRNA complementary to the codon binds to the ribosome and mRNA. This tRNA carries with it the amino acid specified by the codon. The ribosome catalyzes the addition of the amino acid from the new tRNA to the amino acid carried by the initiator tRNA, forming a peptide bond. Using energy, the ribosome and elongation factors remove the initiator tRNA, move the ribosome forward, and accept a new tRNA complementary to the next codon. This process continues to repeat until the ribosome reaches a stop codon.
During termination, the ribosome reaches a stop codon and dissociates from the mRNA. Unlike other codons, the stop codon is not recognized by a tRNA, but instead is recognized by a protein, known as a release factor. Release factor proteins are shaped like a tRNA. The release factor protein and other factors catalyze the release of the polypeptide chain and the dissociation of the ribosome from the mRNA.
What are the sizes for each subunit of ribosomes in pro and eukaryotes?
prokaryotes - 70s, small subunit 30s, large subunit 50s
Eukaryotes - 80s, small subunit 40s, large subunit 60s