Intro to Genetics
What is a gene?
the section of DNA that codes for the primary structure of a polypeptide chain (or tRNA/rRNA)
Explain how replication is semi-conservative
the parent strand of DNA is "pulled apart" such that each strand serves as a template for building a new "daughter" strand, resulting in 2 strands: each has 1 parent and 1 newly-synthesized daughter strand
How is RNA different from DNA?
T is replaced with U
single-stranded
ribose sugar backbone instead of deoxy-ribose
What 3 structures are essential to translation? Describe each.
mRNA - RNA code to be translated
ribosome - catalyst for translation; brings together mRNA and tRNA during translation; small&large subunits
tRNA - RNA molecule that brings amino acids to the ribosome, facilitating the translation of mRNA into protein
A _____ gene is always made and not regulated (although relative number of copies may change), while ____ are turned on/off or up/down.
constitutive; regulated
(The gene encoding for ribosomal RNA is an example of what type of gene?)
___ is a double-stranded polymer of complementary, antiparallel strands of ______ that are held together by ____ bonding between complementary nitrogen bases.
DNA; nucleotides; hydrogen
(Which nitrogenous bases pair together? Is one pair stronger than the other? What does this mean for practical purposes?)
Define okazaki fragment
Short sequences of daughter DNA and primers built along the lagging strand
_________ refers to a collection of related genes that are all controlled by the same promoter and termination sites.
Operon
Describe the process of translation with respect to each of the 3 sites within the ribosome. (slide 1)
the tRNA carrying methionine (initiator) attaches to the P (middle; polymerization) position
a tRNA with the anticodon corresponding to the next codon to be translated attaches to the ribosome at the A position. The amino acid is transfered from the P to the A tRNA in a peptide bond.
The tRNAs translocate, knocking off the previous tRNA from the E site so another tRNA can attach at the A site.
What is the difference between repression and induction?
Repression - transcription stops when the product is present
Induction - transcription starts when the substrate is present
(Are these negative or positive control?)
Explain the difference between chromosomal and plasmid DNA. Discuss the relevant importance of each.
chromosomal DNA is a large, twisted, closed circular molecule contains the genetic blueprint of the cell and all its essential functions
plasmid DNA are small, circular molelcules that encode inducible enzymes for peripheral functions
What are the roles of the following in replication:
helicase
single-stranded binding proteins
primase
DNA polymerase
ligase
unwind double helix
hold open the DNA at the origin of replication ("ori")
lay down primer to "guide" DNA polymerase
attaches DNA to the primer in the 5' to 3' direction
"glues" okazaki fragments together
Discuss the importance of the sigma factor.
recognizes the sequence of the promoter region just upstream of the gene to be transcribed so RNA polymerase can bind
multiple different sigma factors exist because of multiple different promoter regions for multiple different genes/operons
True/False: One mRNA transcript = One complete protein
False. Multiple ribosomes can translate the same mRNA transcript simultaneously (but at different stages).
(What is this called? Why is this advantageous to the cell?)
What is an operator and how is it significant in regulation?
A specific region of DNA near the promoter for a gene or series of genes
If a repressor is activated and binds to the operator, transcription is physically blocked
How is RNA different from DNA? What are the different kinds and their functions?
single stranded
secondary structure involves folding onto itself in regions of complementary pairing
U replaces T; ribose replaces deoxy-ribose
mRNA = template strand for a specific protein
rRNA = primary component of the ribosome (site of protein synthesis)
tRNA = transports amino acids to the ribosome during protein synthesis
What is the difference between the leading and lagging strand?
new DNA is syntheized from 5' to 3'
On the leading strand, new strand is synthesized continuously from 1 primer
On the lagging strand, primase needs to place multiple primers as the DNA is unwound
How is transcription terminated?
inverted repeats form a stem & loop secondary structure; when followed by a run of uracils, transcription stops by releasing the RNA polymerase and mRNA
What are initiation, elongation, and termination?
Initiation: ribosome binds at start codon on mRNA strand
Elongation: ribosome catalyzes peptide bond formation, shifts, continues
Termination: tRNA cannot bind to any stop codon; the release factor binds, cuts off protein, and the ribosome dissociates
negative - prevention of mRNA synthesis by the activity of repressor proteins that are themselves controlled by effector molecules
positive - activates the binding of RNA polymerase to DNA, facilitating transcription
What is a codon? What is the importance of redundancy in codons?
sequence of 3 bases that codes for an amino acid
to account for mistakes
How is replication used for the advantage of science/engineering?
What is the role of RNA polymerase in transcription?
unwinds the DNA double helix, forming a transcription bubble
moves in the direction of 3' to 5' on the DNA strand that is being transcribed so the RNA can be synthesized in the 5' to 3' direction (continuously; antiparallel)
each amino acid is encoded by multiple codons, which are usually closely related; any differences usually occur in the third ("wobble") position (UUA vs. UUG both code for leucine)
(Why is this advantageous to the cell?)
Explain global control and give an example.
Control the use of substrate such that the most energetically favorable substrate is used FIRST. For example, the lac operon is regulated by catabolite repression: When glucose is present, enzymes that metabolize other carbon sources are repressed, since glucose is more favorable.