CH 10: Transcription Flashcards
(41 cards)
What is transcription?
copying DNA into RNA
How does replication differ from transcription?
ex. enzymes, direction, primers, template, initiation
replication - DNA pol, 5’-3’, primers present, both strands are templates, begins at origins
transcription - RNA pol, 5’-3’, no primers needed, 1 strand template, starts at promoters
What is a ribozyme and why is this so special?
a catalytic RNA, can catalyze rxns even though its made of RNA not protein - pointed to RNA being the original genetic material
Primary vs Secondary RNA structure, what is RNA?
RNA - polymer of nucleotides, has sugar, phosphate group, and nitrogenous base joined by phosphodiester bonds, AUGC
primary - nucleotide bases
secondary - RNA folds, hydrogen bonds between complementary bases on folded strand
while DNA is a double helix secondary structure, RNA can be various types of structures
RNA has 2’-OH group
What are mRNA, rRNA, tRNA?
mRNA - messenger, coding instructions for polypeptide chain from DNA to ribosome
rRNA - ribosomal, structural component of the ribosome
tRNA - transfer, links mRNA coding sequence to 3 pair nucleotide that codes for an amino acid
3 major component of transcription?
- DNA template
- RNTPs, raw materials
- transcription apparatus - extra proteins for transcription to occur
All cellular RNAs are synthesized from ? through the process of transcription.
DNA templates
only individual genes that are needed are transcribed
What is the template strand in transcription?
nucleotide DNA strand that is used as a template during transcription
RNA synthesized during transcription is complementary and antiparallel to the DNA template strand
What is the transcription unit?
sequence of nucleotides in DNA that encodes a single RNA molecule
sequences necessary for transcription has:
1. promoter
2. RNA-coding sequence
3. terminator.
What shape do DNA molecules take under transcription?
Christmas tree - RNA molecules come out vertically while being transcribed from DNA
RNA molecules are made in what direction? Characteristics of RNA synthesis?
5’-3- direction, complementary and antiparallel to the DNA template strand
What purpose do rNTPs (ribonucleoside triphosphates) serve in initiation?
rNTPS are added to the 3’-OH group of the growing RNA molecule
RNA does not require a primer but a promoter
The transcription apparatus refers to a complex of proteins and enzymes that facilitate transcription.
What is the special function of bacterial RNA polymerase? What is the core enzyme and sigma factor?
bacteria only has one type of RNA polymerase that starts up synthesis of supporting RNAs (m/t/rRNA)
five subunits make up the core enzyme of bacterial RNA pol
sigma factor - another RNA pol subunit that binds to promoter when transcription starts (E. coli)
Eukaryotic RNA polymerase I, II, III are responsible for transcribing different classes of RNA.
I - large rRNA, large ribosomal RNA
II - pre-mRNA
III - tRNA, small rRNA, involved in regulation
Transcription is broken into ?
- Initiation - transcription apparatus assembles on the promoter and begins the synthesis of RNA
- Elongation - DNA is threaded through RNA polymerase and the polymerase unwinds the DNA and adds new nucleotides, one at a time, to the end of the growing RNA strand
- Termination - recognition of the end of the transcription unit and the separation of the RNA molecule from the DNA template
What are consensus sequences and why are they important in bacteria? What are the most common consensus sequences found in all bacterial promoters?
most commonly encountered nucleotides at each site in a group of related sequences, implies seq has important function
consensus sequences TTGACA at -25 and TATAAT (Pribnow box) at -10
Since no primers are needed for initiation, the location of the consensus seq helps …
determine the position of the start site and helps RNA pol recognize the start site
Bacterial transcription taken care of by RNA pol… what does RNA pol bind to in order to initiate transcription? What complex is formed once RNA binds to _____ ?
RNA pol binds to the sigma factor
RNA pol and sigma factor for a complex known as holoenzyme - binds to consensus seq and then entire promoter
Elongation carried out by ?
RNA polymerase
Transcription stops after the terminator has been transcribed. What are the two major types of bacterial terminators?
Rho-dependent - uses rho factor
Rho-independent - doesn’t use rho factor, hairpin structure formed by inverted repeats followed by UUUUUUU
For genes that have rho-dependent terminators, there is a special site called the _____ site. What happens when RNA pol reaches a terminator site?
rut site - rho factor binds to rut site behind RNA pol
once terminator site is reached by RNA pol, RNA pol pauses and the bound rho factor catches up and uses helicase activity to unwind DNA-RNA and halt transcription
Rho independent termination in bacteria is a _____ process
multistep
transcription halts when inverted repeats form a hairpin followed by a string of UUUUUUU
Where does transcription and translation happen in eukaryotic vs prokaryotic cells?
prok - coupled, happen at same time
euk - transcription (nucleus) translation (cytoplasm)
What is colinearity and how do we see it in euk vs prok cells?
colinearity - refers to that number of nucleotides in a gene is proportionate to the amino acids in the protein
eukaryotes - noncolinear with proteins, there are coding (exons) and noncoding sections (called introns) of the DNA compared to mRNA
bacterial genes/ prokaryotes - colinear with proteins
