Storing and using genetic information
Describe the double helix structure of DNA.
It is a chain of nucleotide monomers that consist of a 2'- deoxyribose sugar, a base and a phosphate group. The DNA forms a double helix structure with 5 prime and 3 prime ends running opposingly.
Describe the structure of a ribosome.
It is comprised of a small subunit and a large subunit. In the large subunit there are two sites, A- aminoacyl site and P- peptidyl site.
What three types of RNA can come from DNA transcription?
Messenger RNA (mRNA) , ribosomal RNA, (rRNA) and transfer RNA (tRNA)
What phase of the cell cycle are chromosomes visible in?
Metaphase due to chromosomes being most compact at this stage.
What are the two amino acids that are coded by only one codon?
Methionine and tryptophan
How does protein synthesis occur in a ribosome?
mRNA tells tRNA what amino acids are needed. So tRNA + amino acid enter A site, peptidyl transferase in P site adds amino acids onto the new polypeptide chain.
What is the fate of proteins after ribosomes?
They are processed in the rough endoplasmic reticulum and the Golgi apparatus.
Which bases are purines and what structure do they have?
cytosine, uracil and tyrosine. Double ringed.
Differentiate between heterochromatin and euchromatin.
Heterochromatin Is condensed and therefore not genetically active. Euchromatin is extended and genetically active.
How is chromatin made me accessible for DNA transcription and replication?
Histones are enzymatically modified and chromatin remodelling complexes displace the histones.
Define a polysome.
A complex formed when multiple ribosomes are translating the same mRNA into proteins.
Which bases are pyrimidines and what structure do they have?
Adenine and guanine. Single ringed.
Define chromatin
Clusters of DNA, RNA, and proteins needed for the packaging of DNA.
Describe the process of chromosome formation.
DNA + 8 histones wrapped around it = nucleosomes -> nucleosome + H1 protein = chromatosome -> these fold and form loops -> compression and tight coiling = chromatid of a chromosome.
Describe DNA translation and replication of the leading stand of DNA.
DNA polymerases pair new nucleotide molecules with the old DNA strand with replication occurring 5' -> 3'.
Describe DNA translation and replication of the lagging strand of DNA.
DNA synthesis starts with a small section of RNA due to the replication occurring in a 3'-5' direction. A different DNA polymerase removes the RNA sections and another one matches new nucleotide molecules. DNA ligases join the Okazaki fragments.
Differentiate between exons and introns.
Exons are areas of a gene that code for proteins. Introns are areas of a gene that don't code for proteins.
Explain what is meant be DNA replication being semi conservative and bi directional.
Semi conservative - because each new molecule of DNA consists of one old strand and one new strand. It is bi directional because one strand runs 5 prime to 3 prime and the other runs in the opposite direction.
Define alternative splicing.
Splicing of introns from the same gene in different ways, each of which produces a distinct protein. (remember introns are the DNA sequences that are non coding in between the exons)
How is DNA stored and why is it stored this way?
Stored as chromosomes to allow compact storage.
How would you differentiate between the p and q arms of a chromosome?
The p arm is always the short arm and the q arm is always the longer arm.
What is the role of mRNA
This carries the information for protein synthesis.
what is the role of tRNA
This translates mRNA into amino acid sequences.
Describe how a specific gene is marked for transcription.
Transcription factors that regulate gene expression bind to a promoter region before the gene which tells the RNA polymerase where to bind. There is also a terminator region at the end of the gene.
What are the three codons that can stop protein translation?
UAA, UAG and UGA.
What is the role of rRNA
We have 4 types that bind to proteins in the cytoplasm to form ribosomes.