Molecualr Genetics Flashcards
What is the chemical make up of DNA?
Sugar phosphate backbone with nitrogenous bases:
- thymine
- adenine
- cytosine
- guanine
Which carbons attach to the phosphates in the backbone of DNA
Carbon 3 and carbon 5 which make the 3 prime and 5 prime end
Where does replication of DNA begin?
Origins of replication where the 2 DNA strands are separated, opening up a replication “bubble”. Replication goes both ways from the bubble
What is the replication fork?
Located at the end of the replication bubble a y shaped region where new DNA stands are elongated
What can DNA polymerase not do?
Initiate synthesis of a polynucleotide; they can only add nucleotides to the 3’ end
What is the initial nucleotide strand?
Short rna primer
What do Enzymes called DNA polymerase do?
Catalyze the elongation of new DNA at a replication fork
What is the rate of elongation?
About 50 per second I’m human cells
How many h bond in a g-c bond? A-t?
G-c 3 a-t 2
What a Okazaki fragments?
The lagging strand synthesizes a series of segments called Okazaki fragments which are joined together by DNA ligase
What do DNA polymerase do?
Proofread newly made DNA, replacing any incorrect nucleotides
What can damage DNA?
Chemicals, radioactive emission, x-rays, uv light, certain molecules (cigarette smoke)
What’s the difference between a bacterial chromosome and a eukaryotic chromosome?
Bacterial is circular and eukaryotic is linear. They both have a large amount of protein though
What’s is chromatin and where is it found?
It is a complex of DNA and protein and is found in eukaryotic cells
What is a histone?
Proteins that are responsible for the first level of DNA packing in chromatin
Describe the forming of chromatin
Starts with 10nm fibre, DNA wind around histone to form nucleosome “beads” on a string of DNA. Then 30 nm fibre is formed be interactions between nucleosomes cause the thin fibre to coil or fold into this thicker fibre. Then 300 nm fibre is formed by the 30nm fibre forms looped domains that attach to proteins. Last the mars phase chromosome is formed by coiling fort her and ending with a width of 700nm
What is the link between genotype and phenotype?
Proteins
What is gene expression and what are the 2 stages of it?
The process by which DNA directs protein synthesis. Transcription and translation
What is the intermediate between genes and the proteins they code?
RNA
What is transcription?
The synthesis of RNA Under the direction of DNA
What does transcription produce?
mRNA
What is translation?
The synthesis of a polypeptide which occurs under the direction of mRNA
What are the sites of translation?
Ribosomes
What separates transcription from translation in eukaryotic cells
The nuclear envelope
What is the central dogma?
The concept that cells are governed by a cellular chain of command: DNA-RNA-protein
How many amino acid are there?
20
Which direction are the codons read during translation
5-3 direction
What’s a codon?
A three letter coding sequence for amino acids
How many stop codons are there?
3
What does the RNA polymerase do
Pries the the DNA stand apart and hooks together the RNA nucleotides
What is the promoter and the terminator?
The promoter is the DNA sequence where the rna polymerase attaches. The terminator is the sequence signalling the end of transcription
What is the transcript unit?
The stretch of DNA that is transcribed
What are the 3 stages of transcription and translation?
- initiation
- elongation
- termination
How many bases at a time does the rna polymerase move along the DNA as it unwinds the double helix?
10-20
In eukaryotes what is the rate the transcription process?
40 nucleotides a second
What the difference between termination in bacteria and eukaryotes?
Bacteria ends when there is a end codon in eukaryotes the polymerase continues until it falls off the DNA strand
What are intervening sequences (introns)?
Non coding regions
What are Exxon’s
Regions of DNA that are expressed
What does rna splicing do?
Removes introns and joins exons, creating a mRNA molecule with a continuous coding sequence
What helps a cell translate mRNA in to protein
tRNA
What are the three binding sites on a ribosome for rna and what do they do?
- P site holds the rna that carries the growing polypeptide chain
- A site holds the tRNA that carries the next amino acid to be added to the chain
- E site is the exit site where discharge tRNA’s leave the ribosome
When does termination occur?
When’s stop codon in the mRNA reaches the A site of the ribosome
What does the release factor do?
Causes an addition of a water instead of an amino acid
What happens after synthesis of the polypeptide chain?
It spontaneously could and folds into its 3D shape
What are the two populations of ribosomes that are evident in cells?
Free ribosomes in the cytosol and bound ribosomes attaches to the ER
What’s a mutation?
Changes in the genetic material of a cell or virus
What’s a point mutation?
Chemical changes in just one base pair
What are the two categories of point mutations and describe
- base pair substitution: replaces on nucleotide and it’s partner with another pair of nucleotides.
- base pair insertion or deletion: additions or losses of nucleotide pairs in a gene
What is a missense mutation?
Still codes for amino acid but maybe not the right one
What’s a silent mutation?
Has no effect because amino acid produced is the same as it should be because of redundancy in the genetic code
What is a nonsense mutation?
Change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
What are mutagens?
Physical or chemical agents that can cause mutations
