Nucleic acids Flashcards
What is a TATA box?
This is a sequence of DNA which indicates to transcription factors where transcription begins. Located upstream from the start of transcription.
What are CGP islands?
Stretches of DNA where there are multiple points at which C is followed by G. They are promoter regions which means that they are a region of DNA which Leeds to the initiation of transcription
How do you ‘switch off’ a CpG island?
It is methylated
How is Eukaryotic pre- mRNA processed?
- ) Addition of a 5’ cap to the beginning of the RNA
- )Addition of a poly A tail (tail of adenine nucleotides) to the end of RNA
- )Splicing
Why is a 5’ cap to the beginning of RNA?
The 5’ cap is added to the first nucleotide in the transcript- this is a modified guanine and it protects the transcript from being broken down. It also helps the ribosome to attach to thTe mRNA during translation.
Why is poly A tail added?
When the polyadenylation signal shows up in the RNA molecule, an enzyme chops the RNA in two at this point. Another enzyme adds around 100-200 adenine nucleotides to the end cut forming a poly A tail.
This protects the mRNA from degradation and is involved in aiding the export of mature mRNA from the nucleus to the cytosol.
What is splicing?
Specific parts of the pre- mRNA called introns are recognised and removed by a protein and RNA complex called a spliceosome. Introns are non coding sections hence they are not important and are removed. Exons are pasted together by spliceosome to make the final mature mRNA.
What is a spliceosome?
A spliceosome is a large and complex molecular machine found primarily within the nucleus of eukaryotic cells. The spliceosome removes introns from a transcribed pre-mRNA, a type of primary transcript.
What is prokaryotic mRNA described as?Why?
Polycistronic. This means that the mRNA can encode for more than one polypeptide
What is the function of RNA polymerase 2?
Makes transcripts from the antisense (templates) strand of DNA
How do we know DNA is the molecule of life?
- Griffith
- Avery
- Hershey and chase
Describe the structure of DNA
- Antiparallel strands
- Has a double helix structure
- sugar phosphate backbone, phosphodiester bond linking adjacent deoxyribose sugars.
- Bases A,T,C,G
Which bases are purines?
Adenine and guanine
Which bases are pyrimidines?
Cytosine and Thymine
Describe the larger scale packaging of DNA
DNA is coiled tightly with the help of histone proteins to form chromatin. Active genes are more loosely coiled as they are used more. Chromatin is condensed to form chromosomes
Briefly describe what Griffiths experiments entailed
Looked at how information could be passed between cells, comparing different strains of disease by checking the effect of different strain of bacteria on mice. The mixing of the two strains together passed on whatever was causing the disease, showing something could be passed on.
• Avery later showed that ‘DNA was the transforming agent as out of purified DNA, RNA, protein, lipid and carbohydrate only DNA from heat killed virulent strain could induce virulence in the non-virulent strain’.
What process is DNA replication?
Semi- conservative
Why is DNA replication describes as semi- conservative?
Because of the two new DNA molecules formed, one strand contains an original strand and the other is newly synthesised DNA.
What is site known as where DNA replication begins?
The origin of replication
What direction does DNA replication occur?
5’ to 3’
Describe the first stage of replication
Replication starts at a specific site called the origins of replication, DNA helices bind to this site and unwind the DNA which is done by breaking the hydrogen bonds between the nitrogenous bases.
What is the error rate for mutations in the DNA?
-An error occurs about once every 100,000 nucleotides inserted into the growing strand of DNA (1 in 10^5).
- DNA polymerases have 3′ to 5′ editing function to remove incorrectly inserted bases. This reduces error frequency to around (1 in 10^7)
- A further check for mismatched bases by other enzymes helps to reduce the overall error frequency to (1 in 10^9) bases
