Lecture 19: Genetic Code II Flashcards
Does it matter which strand of DNA, RNA polymerase transcribes?
Yes, it does because they are antiparallel, RNA polymerase must know which strand to transcribe
Sense strand
Strand that is not transcribed but has the same sequence as the mRNA
Template Strand
Strand that is transcribed and has a complementary sequence to mRNA
What are promoters?
Special sequences on DNA that the RNA polymerase recognize as the start of a gene
Is the promoter sequence transcribed?
No
Which strand is the template strand?
The strand that is in the 5’ to 3’ direction
TATA Box
promoters bind to it
Reading Frames
Different ways to read a genetic sequence
True or False: ribosome picks the right reading frame ?
True
How does the ribosome know where to start?
-The right reading frame always starts with the start codon AUG
-The small subunit finds AUG in the mRNA and binds to it along with the tRNA for methionine
What is the ribosome made of?
Two large subunit of rRNA and proteins
What happens when the large ribosomal sub unit binds?
-The large ribosomal sub unit has two tRNA binding sites, A-site and P-site
-Large subunit binds so tRNA met is in the P-site, the the next tRNA that corresponds to the codon will bind to the A-site
How are peptide bonds between amino acids formed?
- 3’ hydroxyl of amino acid in P-site creates a peptide bond with amino acid in A-site
What happens to the tRNA after the peptide bond is formed?
-tRNA in the A-site is released and then the ribosome shifts a distance of one codon in the 3’ direction
What happens once the ribosome reaches a stop codon?
-A release factor protein binds to the A-Site, causing the last tRNA to release the polypeptide chain and the ribosome to disassemble
Wobble pairing
-The tRNAs can bind to more than one codon
Polysome?
Multiple ribosomes translating the same piece of mRNA
Is the central dogma process sequential ?
No, ribosomes can be translating mRNA before transcription is finished
Missense mutation?
Change in one single amino acid in a protein(SICKLE CELL)
Two broad categories for mutations?
- Point mutations: small changes in the DNA usually only affecting one gene
- Chromosomal Mutations: changes that affect a large portion of a chromosome, often affecting many
genes
True or False: If a change occurs in the sense strand the nonsense strand will also be changed?
True
Silent mutations
Do not affect the proteins because of the degeneracy of the code(point)
Missense mutations
Changes one amino acid to another(point)
Nonsense mutations
Change an amino acid to a stop codon(shortens protein)(point)
Frame shift
insertion/deletion of amino acid (if insertion/deletion happens in three it does not cause a frame shift but does add/delete an entire amino acid)(point)
Deletions
removing a large piece of chromosome including many genes(CM)
Duplications
Duplicate large chunks of the chromosome(CM)
Inversion
Piece of DNA is flipped around, re-entering the chromosome in reverse order(CM)
Translocations
Piece of DNA jumps from one chromosome to another
Reciprocal translocations: two chromosomes trade pieces of DNA(CM)
Mutagens
-Agents that cause changes in the DNA sequence
Ex. Chemicals, Radiation, Viruses
What happens if the mutation is in the somatic cell?
-The change could kill the cell, cause cancer, make the cell sick
-Every cell that derives from that cell will be affected by the mutation
-The change will not be transmitted to the progeny
What happens if the mutation is in the gamete?
There is a possibility that an egg/sperm will end up with the mutated gene and transmit it to the progeny
- It is on these germ lines that natural selection acts
-Can become a new alley in the population if it is not harmful/beneficial
