Chapter 10 Flashcards
What does RNA structure look like? How is it different from DNA structure?
RNA is similar to DNA in terms of the linkage of nucleotides, which are held together by phosphodiester bonds.
Differences:
1. Contains uracil, not thymine
2. Contains ribose, not deoxyribose
3. Usually single-stranded, however, it can form double-strand structures sometimes.
RNA and DNA differences
DNA is double-stranded, forming a double helix. RNA is usually single-stranded. The sugar in DNA is deoxyribose, and in RNA, it is ribose. DNA uses the bases adenine, thymine, cytosine, and guanine. RNA uses adenine, uracil, cytosine, and guanine. DNA doesn’t have an OH group on 2’ position, while RNA does.
What is RNA polymerase?
A multi-unit enzyme that synthesizes RNA molecules from a template of DNA through the process of transcription. Unwinds a short sequence of double
stranded DNA near the promoter.
What is transcription? What is the direction of transcription?
The synthesis of an RNA molecule from a DNA template. The direction of transcription is 5’ to 3’.
What is a promoter?
Where transcription starts. A DNA sequence that lies upstream of the RNA coding region, serves as an indicator of where and in which direction transcription should proceed. The promoter is not actually transcribed; its role is purely regulatory.
What are the template and non-template strands?
The template strand is the transcribed strand, in which DNA is complementary to the RNA being synthesized.
The non-template is the same sequence, but T = U in RNA.
What are the three types of RNA for translation?
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
All three are Bacterial and eukaryotic, all three are in the cytoplasm, and mRNA is also in the nucleus.
rRNA- structural and functional components of ribosome
mRNA- carries genetic code for proteins
tRNA- helps incorporate amino acids into polypeptide chain
What is polycistronic mRNA?
A group of genes transcribed into a single RNA molecule
What does colinear mean?
The idea that a DNA sequence carries a nucleotide sequence that is transcribed into mRNA, mRNA provides the series of codons needed to specify the amino acids required to build a protein. The number of nucleotides in the gene is proportional to the number of amino acids in the protein.
What are the steps of transcription in prokaryotes?
Initiation: Promoter -10 and -35
RNA polymerase (sigma unit)- binding to the promoter when transcription starts; specifies which promoter to bind to
Elongation
Termination: Rho dependent and Rho independent
What is initiation?
Begins at a promoter. Consensus sequences
-10 consensus: 10 bp upstream of the start site
5’ TATAAT 3’
-35 consensus: recruits Sigma factor
TTGACA
Location of the consensus sequence determines the position of the start site. During initial RNA synthesis, no primer is required.
What is elongation?
RNA elongation is carried out by the action of RNA polymerase
What is termination? What is Rho-dependent and Rho-independent termination?
Termination has two main types in prokaryotes.
Rho-dependent- Uses rho factor. Binds to a Rut site in the mRNA and chases the RNA polymerase.
Rho-independent- Hairpin structure formed by inverted repeats, followed by a string of uracils. Inverted repeat sequence cause a hairpin to form in the mRNA and release from the DNA.
What are the three post-transcriptional modifications of primary transcript?
- 5’ Methyl guanosine cap
-Poly(A) tail
-Removal of introns (For mRNA between GU and AG,
Alternative splicing, spliceosome)
What does the addition of the poly(A) tail do?
50 to 250 adenine nucleotides are added to the 3’ end of the mRNA
