Transcription and Targeting Flashcards
What is a polysome?
An mRNA molecule that is covered in multiple ribosomes.
What is the difference between DNA and RNA?
DNA is double stranded whereas RNA is single stranded.
DNA uses the sugar deoxyribose whereas RNA nucleotides use the sugar ribose.
DNA can include the base Thymine whereas RNA cannot, instead, it uses Uracil.
What is the 3 main types of RNA
- mRNA - involved in transcription. Enables the gene to leave the nucleus so it can be translated into a protein.
- tRNA - involved in translation. Bringing the amino acid specific to the codon on the mRNA sequence.
- rRNA - makes up the ribosome along with proteins.
What is the TATA Box?
It is a promoter region. It signals that transcription needs to occur downstream of the TATA box. The majority of genes however do not have a TATA box. The region is made up mostly of Ts and As. IT is often 25-30 nucleotides upstream form the gene.
What is the initation step of transcription?
Initiation factors bind to the promoter region to form a complex. RNA Polymerase II can then bind.
What is a CpG island and how are they involved in switching off genes?
A CpG island is an area where Cytosine bases are followed immediately after Guanine bases in a sequence. The nucleotides are joined by esterfication. This island protects the genes from methylation - which switched off the gene. If not in an island, Cytosine can be converted into 5-methylcytosine, switching off the gene. These islands are more frequently the promoter. This methylation occurs extensively in X-inactivation. Transcription of the non-coding RNA molecules of unknown function is driven by CpG islands.
How to cytosolic ribosomes become membrane bound?
The mRNA encodes for a secretory protein. The mRNA is translated. The first section is usually for hydrophobic amino acids. This stretch if hydrophobic amino acids is called a ‘signal sequence’. The signal recognition particle binds to this and cause the ribosome to dock to the endoplasmic reticulum. This particle is a cytosolic ribonucleoprotien that recognises and targets proteins to the ER. The protein is then fed through the ER as it is translated.
What modifications can be made to the protein in the ER and Golgi apparatus?
- disulphide bridges
- sugar side-chains are added
How is a transmembrane protein made?
Translation continues until a length of approximately 20 consecutive hydrophobic amino acids are made. This then spans the length if the plasma membrane and embeds in the membrane.
How is pre-proinsiulin converted to insulin.
Pre-proinsulin is cleaved from the ER. Disulphide bridges then form to form proinsulin. The connecting C-peptide loop is then cut off using proteases to form insulin.
Why can yeasts be used to produce certain hormones that bacteria cannot?
Yeast glycoserate their hormones whereas bacteria do not.
What modifications must be added for pre-mRNA to become mature mRNA?
- a 5’ cap must be added
- Polyadenylation
- Splicing
What is the 5’ cap? Why is it added?
7-methylguanosine is added to the end of the pre-mRNA. This stops degradation of the mRNA by enzymes in the cytosol. It also acts as a signal to begin translation form that end.
What is polyadenylation?
The enzyme Poly A polymerase adds a long sequence (variable) of adenine nucleotides onto the 3’ end of the pre-mRNA. ItThis protects the mRNA being degraded by enzymes from the 3’ end. It also signals that the mRNA is complete and that translation can begin.
Do all mRNa molecules have a poly a tail? Do bacterial mRNA molecules have poly a tails?
No, those that encode for histones do not?
Bacteria mRNa molecules do have poly a tails.
