Studied by 36 people
Dr. Lydia Villa Komaroff
Molecular and cellular biologist
3rd Mexican-American woman to receive Dr. in science
Completed PhD at MIT in 1975
Post doctorate research at Harvard medical school
Taught of UMMS and Harvard Medical School
Discovered insulin can be produced by bacteria
One gene, one polypeptide hypothesis
Hypothesized that each gene contains the information to make one enzyme
What is Neurospora crassa?
A type of bread mold
What did the one gene, only polypeptide hypothesis focus on?
The metabolic pathway that synthesizes arginine
What is arginine?
a key amino acid needed for proteins
What are the three enzymes in the arginine pathway?
Enzymes 1,2 and 3 - help produce Ornithine, Citrulline, and Arginine respectively.
How was the arginine study set up?
The scientists isolated 3 mutant N. Crassa that were deficient in one of the three enzymes in the arginine pathway?
What did the arginine study conclude?
Mutants for certain genes lacked specific enzymes needed for the pathway.
Concluded that each gene coded for one “enzyme”
What do scientists now know about the one gene, one polypeptide hypothesis?
Genes contain instructions for not only enzymes but any protein
What is the central dogma?
The flow of information from DNA to proteins
How does the central dogma work?
Sequences of bases in DNA specify the sequences of bases in mRNA which specifies the sequences of amino acids in a protein
Protein account for how much dry mass in cells?
More than 50%
Functions of proteins:
Speed up chemical reactions
Defense
Storage
Transport
Cell communication
Movement
Structural support
hormones (insulin)
Proteins are [Blank] with [blank] as their monomers.
Polymers, amino acids
Peptide bonds form between
each amino acid
polypeptide chains are
the polymer form of a protein
What is the link between DNA and protein?
Messenger RNA (mRNA)
DNA codes for
RNA sequence
RNA codes for
sequence of amino acids in a protein
transcription
uses DNA template to make complementary RNA
translation
use information in mRNA to synthesize proteins
Organism’s genotype (DNA) determines the
phenotype (Proteins)
Where does transcription take place?
the nucleus of a eukaryotic cell
Where does translation occur?
the cytoplasm, specifically within a ribosome (either free-floating or in the RER)
How are these processes different in a prokaryotic cell?
A prokaryotic cell has no nucleus, so they both take place in cytoplasm.
Three-base code referred to as
triplet code
Codon
group of 3 bases that specifies a particular amino acid
Start codon
only one (AUG), codes for methionine and will be important for the beginning of translation
Stop codon
three stop codons (UGA, UAA, UAG), do not code for an amino acid and result in the end of translation
In order for the code to work, the correct…
reading frame, or sequence of codons is needed.
Genetic code is: redundant-
all but two amino acids are encoded by more than one codon
Genetic code is: unambiguous-
one codon never codes for more than one amino acid
Genetic code is: non-overlapping
codons are read one at a time
Genetic code is: Nearly universal
all codons specify the same amino acids in all organisms
Genetic code is: conservative
if several codons specify the same amino acid, the first two bases are usually identical
Mutations are…
changes in the genetic information of the cell
What are point mutations?
changes in just one nucleotide pair of a gene - can lead to production of an abnormal protein
Mutations can be
Beneficial- increase fitness
Neutral - do not affect fitness
Deleterious - decrease fitness
Silent mutations -
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
Missense mutations
still code for an amino acid, but not the correct one
Nonsense mutations
change an amino acid codon into a stop codon, most lead to a nonfunctional protein
Frameshift mutation*
add or delete a nucleotide, almost always deleterious
Sickle cell anemia
affects the shape of RBCs and leads to low RBC count, pain, swelling, infections, etc.
What type of mutation is present in the Sickle Cell gene?
Missense mutation
Chromosome mutations: Deletion
segment of chromosomes is lost
Chromosome mutations: inversion
segment of chromosome breaks off, flips around and rejoins
Chromosome mutations: Duplication
segment of chromosome is present in multiple copies
Chromosome mutations: translocation
section of chromosome breaks off and becomes attached to another chromosome
Chromosome mutations can be
Beneficial, Neutral, or deleterious
Cancer cells exhibit
numerous deleterious chromosome mutations
Dr. Venki Ramakrishhnan
Indian-born British and American structural biologist
BS in physics
Completed PhD in Physics in US
Transferred to biology at UCSD
Worked on ribosomes at Yale
Work for determining 305 subunit of the ribosome
Shared Nobel prize in chemistry
In what direction do RNA polymerases make mRNA from a template DNA strand?
5’ to 3’ direction
What makes RNA polymerase different from DNA polymerase?
RNA polymerase does not require an RNA primer
Prokaryotic cells have how many RNA polymerases?
One
How many RNA polymerases do eukaryotic cells have?
Three
Three stages of transcription.
Initiation
Elongation
Termination
Where does transcription occur in a prokaryotic cell?
holoenzyme
What is the holoenzyme made up of?
The core enzyme which is a RNA polymerase and sigma
How does initiation begin in prokaryotes?
Sigma recognized a promoter in the DNA
What are promoters?
Segments of DNA that are 40-50 base pairs long
Will be recognized by sigma within the holoenzyme and allow the start of transcription
/Once bonded to the holoenzyme, RNA polymerase will…
Open up the double helix
begin adding new nucleotides
During prokaryotic elongation…
the RNA polymerase will add new nucleotides to the growing 3’ end of the RNA
Prokaryotic termination happens when
the RNA polymerase transcribes a “transcription-termination signal”
What happens when the “transcription-termination signal” is transcribed?
The RNA polymerase will separate from the RNA transcript
What is different about the promoters in eukaryotic transcription?
The promoters are larger, including TATA box
What recognizes the promoter in place of the sigma protein?
Transcription factors
What leads to the termination of eukaryotic transcription?
A poly-A signal is transcribed
What type of cells will require RNA processing?
Just eukaryotic cells
What needs to occur to the primary transcript within eukaryotic cell?
Splicing
Addition of caps and tails
The 5’ end of the primary transcript receives….
a modified nucleotide, known as 5’cap
The 3’ end of the primary transcript receives…
a poly-A tail
Why do caps and tails need to be added?
Facilitate export of mRNA to the cytoplasm
protect the mRNA from hydrolytic enzymes
help ribosomes attach to the 5’ end
What is the purpose of RNA slicing?
creates an mRNA molecule with a continuous coding sequence
In RNA splicing, introns must be…
removed
In RNA splicing, exons must be…
joined
What is the site that mRNA is translated into protein?
Ribosomes
What is unique about transcription and translation in a prokaryotic cell?
Ribosomes can begin translating before transcription is complete
How do transcription and translation run in a eukaryotic cell?
Separately
What does each transfer RNA (tRNA) carry?
A specific amino acid on one end
What is present on the other end of a tRNA molecule?
An anticodon
What is an anticodon?
three base pairs that attach to a complementary codon on mRNA
What do ribosomes allow for?
tRNA anticodons to recognize mRNA codons
What are ribosomes made up of?
ribosomal RNA (rRNA)
Translation initiation occurs when…
the start codon (AUG) signals
During initiation of translation…
small ribosomal subunit binds with mRNA and a special initiator tRNA
Translation elongation
amino acids are added one by one to the end of the growing chain
What direction does elongation proceed in translation?
Along the mRNA in the 5’→3’ direction
Elongation continues until….
a stop codon is read
What do stop codons code for?
release factors
Dr. Tracy L. Johnson
American geneticist
BA in Biochemistry and cell biology form UCSD
PhD in Biochemistry and Molecular Biology from UC
Studied RNA splicing at Cal IT
Focuses on gene regulation, chromatin modification, and RNA splicing
Known for work in diversity, equity, and inclusion in STEM
operon
set of operator and promoter sites and the structural genes they control
operator
acts as a go or a stop signal for transcription
promoter
segment of DNA where RNA polymerase initiates transcription
Negative regulation
Repressor protein
Repressor can bind to segment of DNA and block transcription from occurring
Includes both repressible and inducible operons
Positive regulation
Activator protein
Activator binds to segment of DNA to turn on transcription
Repression operon
Trp
Induction operon
Lac
Trp is short for
Tryptophan
What is feedback inhibition used for in this unit?
Starting and stopping the production of enzymes
Repression:
decreases gene expression and decreases enzyme synthesis
Note 
Flashcard (43)