Lecture 12: Chapter 15 (Genes and how they work) Flashcards
What did Archibald Garrod (1902) propose after he recognized that alkaptonuria is inherited via a recessive allele and that patients with the disease lacked a particular enzyme?
The ideas connected genes to enzymes
When was Beadle’s and Tatum’s experiment?
1941
What did Beadle and Tatum study?
They studied a bread mold, Neurospora
What did Beadle and Tatum use to damage the DNA of Neurospora?
X-rays
In their experiment, what did Beadle Tatum look for, and how did they identify it?
They looked for nutritional mutations by identifying spores unable to grow on minimal media
What did Beadle’s and Tatum’s minimal media contain?
glucose+ vitamin (biotin)+ salts
What is
Gluatamate–> Ornithine–> cirtuline–> arginosuccinate–> arginine?
The arginine synthesis pathway
What strains did Beadle and Tatum isolate?
The strands that could not grow unless fed arginine
What did Beadle and Tatum feed the isolated strands to test for growth?
The intermediates in the pathway
What was required for the biochemical pathway to produce the amino acid arginine?
enzymes
How did Beadle and Tatum identify mutants deficient in each enzyme of the pathway?
By supplementing minimal media with biochemical intermediates
What hypothesis did Beadle and Tatum come up with from their experiment?
One-gene/ one-enzyme
What has the one-gene/ one enzyme hypothesis been modified to?
one-gene/one- polypeptide hypothesis
What does the central dogma describe?
information flow
Who was the central dogma first described by?
Francis Crick
How does information flow?
DNA–> RNA–> protein
What part of the information flow is transcription?
DNA_-> RNA (both nucleic acids)
What part of the information flow is translation?
RNA–> Protein (from nucleic acid to protein)
How do retroviruses violate the information flow?
They use reverse transcriptase to convert their RNA genome into DNA
What are the steps of Transcription?
- DNA-directed synthesis of RNA
2.Only one strand of DNA copied as RNA
What strand in transcription is copied as RNA?
the template strand (sense)
What is the strand in transcription that is used as a template called?
noncoding strand (antisense)
In RNA, what is thymine replaced by?
Uracil
What is used to direct synthesis of polypeptides in transcription?
mRNA
T or F: all RNA is synthesized from a DNA templated by transcription
True
What kind of RNA is part of the machinery involved in the processing of “pre-mRNA” in splicing?
small nuclear RNA (snRNA)
What kind of RNA is a mediator for proteins synthesized on the rough ER?
signal recognition particle RNA (SRP RNA)
What kind of RNA is involved in control of gene expression?
small RNAS
What are the two types of small RNAS?
miRNA and siRNA
About the genetic code, what did Francis Cric and Sydney Brenner determine?
How the order of nucleotides in DNA encoded amino acid order
What is a block of three DNA nucleotides corresponding to an amino acid called?
codon
What type of mutation deals with inserting or deleting a single nucleotide?
frameshift mutations
If you add or delete 1 or 2 nucleotides, what does it shift?
the genetic message
If you add or delete 3 nucleotides, what is the result?
the addition or deletion of a protein
What did Crick and Brenner conclude from their experiments of adding and deleting nucleotides?
That the genetic code is read in increments of three nucleotides, and read continuously
T or F: Codons specify amino acids
True
Who identified the codons that specify each amino acids?
Marshall Nirenberg
What do stop codons do?
They terminate translation
How many start codons are there, and what are their names?
Three
1. UAA
2.UGA
3. UAG
What does the start codon do?
It signifies the start of translation
How many start codons are there, and what are their names?
- AUG
Genetic code is ________, which means that some amino acids are specified by more than one codon.
degenerate
T or F: Genetic code is practically universal
True
What is the most substantial evidence that all living things share a common ancestry?
That genetic code is practically universal
What two organelles of the cell have some differences in genetic code?
Mitochondria and chloroplast
How many RNA polymerases do prokaryotes have?
a single RNA polymerase
What are the two forms of RNA polymerase?
- core polymerase
- Holoenzyme
Why is the Holoenzyme needed for RNA polymerase?
Because its addition of the sigma subunits is needed to accurately initiate synthesis
What does transcription not require?
a primer
What forms the recognition and binding site for RNA polymerase in transcription?
the promoter
What is the actual site where RNA synthesis begins in transcription?
start site
What signals the end of transcription?
The Terminator
What is the region from the promoter to the terminator called?
the transcription unit
What are some characteristics of the promoter?
- found upstream of the start site
- not transcribed
- it is asymmetrical- it indicates the site of the initial and direction of transcription
What are the steps of transcription: elongation?
- RNA chains grows in the 5’ to 3’ direction as ribonucleotides are added
- After the transcription bubble passes, the now-transcribed DNA is rewound as it leaves the bubble
What complex contains RNA polymerase, DNA template, and growing RNA transcript?
Transcription bubble
T or F: termination occurs at specific sites
True
What happens when the stop signal is sequenced to RNA polymerase?
1.RNA-DNA hybrid within the transcription bubble dissociated
2. RNA polymerase release the DNA
3. DNA rewinds
What is the series of G-C base- pairs followed by a series of A-T base-pairs in transcription called?
the simplest terminator
How does the simplest terminator work?
It forms a hairpin, which results in the dissociation of RNA from DNA in the transcription bubble
What does the hairpin cause in transcription?
RNA polymerase to pause at uracil
What bonds are the weakest bonds in transcription?
U-A
In prokaryotes, what are coupled together?
transcription and translation
How are transcription and translation coupled?
mRNA begins to be translated before transcription is finished
How many RNA polymerases do Eukaryotes have?
Three
In Eukaryotes, what does RNA pol I do?
transcribes rRNA
In Eukaryotes, what does RNA polymerase II do?
It transcribes mRNA and some snRNA
In Eukaryotes, what does RNA polymerase III do?
it transcribes tRNA an some other small RNAS
Each RNA polymerase recognizes its own _____
promoter
RNA pol I promoters are ______ specific
species
RNA Pol II promoters consist of a ______ promoter which includes the _____ _____
core, tata BOX
Where are most RNA pol III promoters found?
within the gene itself
IN Eukaryotes, what causes the initiation of transcription?
the pol II promoters
Why are RNA pols II required in transcription?
- they ae necessary to get the RNA pol II enzyme to a promoter to initiate gene expression
- They interact with RNA polymerase to form initiation complex at promoter
What structural feature coordinates elongation complex factors?
the carboxyl terminal domation (CTD)
In eukaryotes, the primary transcript must be modified to become ______ mRNA
mature
What does mature mRNA consist of?
- addition of a 5’ cap
- addition of 3’ poly- A- tail
- removal of introns
