RNA/DNA Flashcards
What are Okazaki fragments?
The synthesised fragments of DNA ready to be spliced together to form lagging strand.
What and which molecules are pyrimindines and purines?
Pyrimindines - single ring structure. Thymine, Cytosine, and Uracil
Purines - double ring structure.
Adenine and Guanine
What observation demonstrates Hershey and Chase’s experimental design?
DNA contains PHOSPHATE and PROTEIN contains SULFUR
Strands of DNA are held together by?
Weak hydrogen bonds
In DNA Replication, both strands cannot be synthesised because?
Chains extend in one direction only: 5’ to 3’
(3’ end is more electronegative)
By what and how can DNA be damaged?
Chemical agents (mutagens)
High energy radiation (UV/X-rays)
Increases the rate of mutation, leading to proteins of altered sequence and function.
How is Mitochondrial DNA passed on and what’s unique about it?
It can pass on from generations via maternal lineage and does not mix.
Useful for analysis of family history.
When mutations occur it causes many different diseases centered around not generating enough energy.
Describe evidence for link between genes and proteins.
Genes act by regulating definite chemical events.
The mutants are unable to carry out a step in the pathway due to a lacking intermediate (normally the mRNA). Genes do not build - simply code for them, hence indirect link.
Garrod (1909) studied patterns of inherited diseases (ablinism/alkaptonuria) where symptoms of a person with the disease caused the inability to make a particular protein(enzyme).
Genes dictate phenotypes, therefore results in lack of particular protein in the gene.
Beadle and Tatum studied link using mutants (using x-rays) of bread mould. Studying mutations in pathway where amino acid is synthesised.
Describe replication of RNA polymerases and explain DNA template role during Transcription.
RNA Polymerase = catalyst enzyme
-Enzyme unwinds double helix, making a complementary copy of one strand of the template of DNA.
-Uses triphosphates to supply nucleotide units to grow RNA chain.
-RNA chain grows in 5’ to 3’ direction only.
-No Proof-reading, but error is extremely rare.
Explain how RNA polymerase finds start of gene and makes transcript of template DNA strand in the correct direction.
RNA Polymerase is bound to the promoter through a set of proteins (transcription factors) (TATA box) in eukaryotes.
In prokaryotes, RNA Polymerase is able to recognise the promoter and bind to it by itself.
Describe how RNA transcripts in eukaryotic cells are processed into mature transcripts and transported to correct location in cell.
1-A cap is added to 5’ end
2-polyA (50-200 nucleotides) tail to 3’ end
(protects from degradation, aids export from nucleus, helps anchor mRNA in ribosomes)
3-mRNA is spliced by snRNPs (small nuclear RNA 150 nucleotides long + proteins) introns are removed and exons are retained
4-spliceosome complex formed
5-alternate RNA splicing leads to male/female drosophila
6- mature mRNA transcript is produced
(short intron sequence mark splice sites, snRNPs play catalytic & structural role as ribozymes, splicing allows for larger range of proteins to be synthesised)
What are Mendel’s Laws?
Law of Dominance: Some alleles are dominant over others, and an organism will exhibit the dominant trait if it inherits at least one dominant allele.
Traits that are not dominant are recessive.
Law of Segragation: During gametogenesis, the two alleles for each gene separate, and each parent passes on one allele to their offspring.
An organism’s genotype is the set of alleles it carries, and its phenotype is its observable features.
Law of Independent Assortment: Alleles of different genes are inherited independently of one another.
This law is usually accurate for multiple genes, but it’s not accurate for genes on the same chromosome.
Why are proteins translated indirectly via mRNA and not from DNA?
Because the languages of code are different.
3 stages during Transcription?
3 stages:
INITIATION:
-site known as promoter, contains particular sequence of bases
-prokaryotes, enzyme recognises and binds to promoter site
-eukaryotes, set of proteins are involved in binding of enzyme to promoter.
ELONGATION:
-local unwinding of helix and addition of nucleotides
-DNA rewinds as enzyme proceeds along template
-many RNA Polymerases can be transcribing a gene at same time
-allows large amounts of protein to be synthesised
TERMINATION:
-signalled by sequence of RNA script
-after terminator sequence, proteins bind growing transcript and cut free from polymerase
-transcript is released and enzyme detaches from DNA
What are the 3 types of RNA?
mRNA - messenger
rRNA - ribosomal
tRNA - transfer
In prokaryotes all RNA is?
All RNA is made by single RNA polymerase.
