From Gene to Protein

Question 1

how did archibald garrod propose the gene / protein relationship?

Answer 1

-suggested that genes and phenotypes are directly related
-enzyme presence / absence was due to a genetic defect

Question 2

what experiments did beadle and tanum perform?

Answer 2

-created genetic mutants out of bread mold
-non mutants grew on minimal medium & synthesized necessary nutrients on their own
-when mutants were exposed to an additional nutrient, they developed a mutation to synthesize that nutrient

Question 3

what experiments did srb and horrowitz perform?

Answer 3

-found a pathway for arginine production that involved precursor amino acids as well as a 4 step process that needed an enzyme at each step
-if an enzyme at one precursor step was not present, the process could not continue unless the next product was artificially added in
-tldr - further evidence for the “one gene = one enzyme” hypothesis

Question 4

what is the one gene - one enzyme hypothesis ? (also called one gene - one polypeptide)

Answer 4

-the idea that a gene dictates the production of a specific polypeptide or enzyme

Question 5

how does a gene become a polypeptide?

Answer 5

-DNA strand stays in the nucleus
-DNA is read 5’ to 3’
-DNA template strand is read and forms a mRNA non-template strand

Question 6

what is RNA, what does it do, and how does it differ from DNA?

Answer 6

-RNA is a transcribed message / code read from DNA
-RNA is translated into a protein in the cell cytoplasm
-RNA contains a uracil base instead of a thymine base, and is single stranded as opposed to DNAs double strand

Question 7

what are transcription and translation?

Answer 7

-transcription = creates RNA strand from DNA in nucleus
-translation = creates polypeptide from RNA strand in cytoplasm, more specifically ribosomes

Question 8

how does transcription and translation differ in prokaryotes / eukaryotes?

Answer 8

prokaryotes = can perform transcr. and transl. at the same time in the cytoplasm
eukaryotes = transcription occurs in nucleus, mRNA must then be modified before being translated in cytoplasm

Question 9

how do genes code for proteins? what is the triplet code system / codon?

Answer 9

-genes code for proteins by containing a sequence of 3 nucleotides called the “triplet code system”
-mRNA with the 3 nucleotides is a “codon”
-1 codon = 1 amino acid

Question 10

how many codons are there and what kinds are there?

Answer 10

-64 possible codons
-1 start codon (AUG) and 3 stop codons (UAA, UAG, UGA)
-20 possible amino acids that the codons can correspond to

Question 11

what does genetic code being universal and unambiguous mean?

Answer 11

-genetic code is the same across all organisms: CCG will always translate into proline in all organisms
-unambiguous = CCG only codes for proline and nothing else

Question 12

what are the three stages of DNA transcription?

Answer 12

-initiation
-elongation
-termination

Question 13

what occurs during DNA transcription?

Answer 13

-mRNA is transcribed from DNA by reading a “transcription unit”: a sequence of DNA that creates a single RNA molecule

Question 14

what occurs during transcription initiation?

Answer 14

-RNA polymerase opens up the DNA to begin the process
-reads DNA 3’ to 5’, forms a strand of mRNA that is 5’ to 3’
-forms a pre-mRNA strand

Question 15

what is the promoter region and what does it contain?

Answer 15

promoter region = the initiation site for RNA synthesis. contains a binding site called the TATA box

Question 16

what is a transcription factor?

Answer 16

-transcription factors are proteins that attach to the TATA box
-this enables RNA poly. to attach and begin transcription

Question 17

what occurs during transcription elongation?

Answer 17

-DNA bases are continuously added to the pre-mRNA strand, transcribed according to the template strand
-formed 5’ to 3’

Question 18

what occurs in transcription termination?

Answer 18

-RNA poly. transcribes a termination sequence - AAUAAA that releases the pre-mRNA strand

Question 19

what occurs during RNA processing in eukaryotes?

Answer 19

-a 5’ cap is added to the front of the pre-mRNA as well as a poly-A tail
-these work to protect the strand from being degraded by cellular enzymes

Question 20

what occurs during RNA splicing in eukaryotes?

Answer 20

-introns [non necessary info] are removed by a protein complex called a spliceosome
-exons [necessary info] are spliced together

Question 21

what are the key players in RNA translation?

Answer 21

-ribosomes
-tRNA
-mRNA
-enzymes

Question 22

what is tRNA and what does it contain?

Answer 22

-tRNA = translation RNA, carries amino acids to a ribosome to add them to a polypeptide chain
-tRNA contains an anticodon that is opposite to the mRNA codon

Question 23

how do the correct amino acids get joined to a tRNA molecule?

Answer 23

-through an enzyme called aminoacyl-tRNA synthetase

Question 24

what are the three sites of a ribosome?

Answer 24

A Site = holds tRNA that has the next amino acid in a chain
P Site = holds tRNA that carries the growing chain
E Site = exit site, where discharged tRNAs leave the ribosome

Question 25

what are the three stages of translation?

Answer 25

-initiation
-elongation
-termination

Question 26

what occurs during translational initiation?

Answer 26

-tRNA brings in first anticodon amino acid, and top unit of the ribosome binds with the small subunit

Question 27

what occurs during translational elongation?

Answer 27

-amino acids are added to the A site one by one, and the P site polypeptide chain begins to grow

Question 28

what occurs during translational termination?

Answer 28

-when the ribosome reads a stop codon in the mRNA, a release factor binds in the A Site and the ribosome breaks apart

Question 29

what post translational processing can occur?

Answer 29

-the resulting polypeptide chain can be modified after being completed
-the type of ribosome the mRNA is read through can impact where it goes (ex - free floating or an attached ribosome)

Question 30

why can prokaryotes transcribe and translate at the same time?

Answer 30

-their cells lack a nuclear envelope, thus the mRNA does not need to leave to join with a ribosome. similarly, eukaryotes need to undergo mRNA processing after transcription

Question 31

what is a polyribosome?

Answer 31

several ribosomes translating a single mRNA

Question 32

what are mutations?

Answer 32

-a permanent change in the DNA
-are heritable, and can create new genes that code for different proteins

Question 33

what are base pair substitutions?

Answer 33

when one nucleotide (and therefore its corresponding one as well) are replaced with another pair of nucleotides

Question 34

what are the types of base pair substitutions?

Answer 34

silent = substitution has no effect on the protein that is coded
missense = substitution changes what amino acid is coded for. can have little or serious effects
nonsense = substitution changes an amino acid into a stop codon

Question 35

what are base pair insertions / deletions?

Answer 35

-when nucleotide pairs are added or removed in a gene due to a mutation

Question 36

what is a base pair frameshift?

Answer 36

-when a base pair mutation alters the reading order of nucleotides to no longer be a pair of 3

Question 37

what are mutagens?

Answer 37

physical or chemical agents that can cause mutations

Question 38

what is the dogma definition of a gene?

Answer 38

a gene is a region of DNA whos final product is either a polypeptide or an RNA molecule