Unit 5 Flashcards
DNA replication uses __________________to make a _____________________ strand from the original _____________.
DNA replication uses DNA polymerase to make a complementary strand from the original DNA template
What does transcription make?
RNA
Translation uses __________________ to make _______________ from mRNA.
Translation uses ribosomes to make proteins from mRNA.
What are the 3 different types of RNA involved in making proteins?
mRNA
tRNA
rRNA
If I were to make a RNA sequence to this DNA sequence (3’-TACGGGCCCTTCGATAAT-5’),
What would it be?
T → A
A → U
C → G
G → C
Adenine (A) pairs with Uracil (U) in RNA.
Thymine (T) pairs with Adenine (A) in RNA.
Cytosine (C) pairs with Guanine (G) in RNA.
Guanine (G) pairs with Cytosine (C) in RNA.
In what location within the cell that translation can occur? (Hint: think about the organelle(s) that have ribosomes.)
Attatched to Rough ER in eukaryotes
Free ribosomes in the cytoplasm
DNA polymerase can only add bases to the ______ end of the nucleic acid
Which means DNA polymerase ______ start replication from scratch
Can only add bases to the 3’ end of the nucleic acid;
Which means DNA polymerase can only add bases to a nucleic acid and it cannot start replication from scratch
Primase is an enzyme that cells use to synthesize a short piece of RNA called _______
an RNA primer
DNA polymerase is an enzyme that ______
Powered by bond of _______
catalyzes the addition of bases to the 3’ end of the growing DNA molecule;
Powered by bond of nucleotide triphosphates
What dictates which base is added in the strand?
Hydrogen bonding between the parental strand and the nucleotide triphosphates
RNAse:
An enzyme that removes the RNA primers leaving a gap in the DNA which can be filled by DNA polymerase
DNA ligase:
Seals the gaps between the DNA fragments created during synthesis of the lagging strand
What are the products of semiconservative replication for a double-stranded DNA molecule?
Two double-stranded DNA molecules;
each consisting of one parental strand and one daughter strand
Why is DNA replication essential for a cell?
An organism must copy its DNA to pass genetic information to its offspring
What is the function of the parental DNA in replication?
It serves as the template for DNA replication
Identify the stages in which the lagging strand is synthesized (4)
- DNA polymerase begins synthesizing the lagging strand by adding nucleotides to a short segment of RNA.
- After each piece of the lagging stand is complete, it is released from DNA polymerase.
- A different DNA polymerase replaces the RNA segments with DNA.
- DNA ligase seals the gaps between the pieces, and eventually forms continuous strand.
What is the difference between DNA and proteins?
DNA stores information and Proteins are used to perform activities necessary to keep the cell alive
Describe the process of transcription
The information stored in the DNA molecule is copied into RNA molecules which can be used to synthesize specific proteins
Describe the different type of RNA cells use
rRNA: used to form ribosomes
tRNA: deliver amino acids to ribosomes
mRNA: carry the information for making specific proteins from DNA to ribosomes
What RNA’s does transcription produce?
mRNA, tRNA, and rRNA
What makes mRNA from the information stored in a DNA template?
RNA polymerase
What are ribosomes made of/contain?
rRNA
Which RNA is involved in bringing amino acids to the ribosomes?
tRNA
What RNA can be translated into protein?
mRNA
Describe the process of translation:
The process by which the information contained in a molecule of mRNA is used to synthesize a protein
Why is it called translation?
Because ribosomes read along the mRNA molecule translating the genetic code into the amino acid sequence of the protein
Because there are no nuclei in bacteria, Translation ______
can actually begin before transcription is completed
What results from the process of translation?
A polypeptide
How is bacterial translation different from eukaryotic translation?
Bacteria can begin translation before transcription has terminated
Ribosomes move along the mRNA in which direction?
5’ to 3’ (mRNA)
What are Okazaki fragments?
Short DNA segments synthesized on the lagging strand during DNA replication, which are later joined to form a continuous strand
Okazaki fragments are formed because DNA replication __________
is discontinuous on the lagging strand
What is a characteristic of prokaryotic genomes but NOT eukaryotic genomes?
circular chromosomes
What is the lac operon?
The lac operon is a cluster of genes in bacteria that encodes proteins necessary for the metabolism of lactose;
It is regulated by the availability of lactose and glucose, allowing the bacteria to efficiently utilize lactose when it is present
What is the inducer molecule in the lac operon?
Lactose (Allolactose)
With which genetic region does the repressor protein interact?
The operator region;
to block transcription of the downstream genes (lacZ, lacY, and lacA) when lactose is not present
When the cell is not in the presence of lactose ___
(what binds to what)
the repressor proteins bind to the operator
What is the basic function of the lac operon?
To catabolize lactose when it is present
To what genetic element does the RNA polymerase bind?
The promoter
Consider a lac operon in which there is a mutation that causes a stop codon to appear early in the first structural gene. Assuming the RNA polymerase can bind and the operator is not blocked, what would be the result?
The operon would be transcribed, but not translated correctly;
A stop codon causes translation to stop, terminating the polypeptide. Thus, the operon would be transcribed completely
Consider a lac operon in which there is a mutation in the gene for the repressor molecule. The repressor is still able to bind to the operator, but cannot bind to lactose (or allolactose). What would be the result?
The operon would always be turned off;
This would cause the repressor to permanently attach to the operator, thus always preventing transcription
Consider a lac operon in which there is a mutation that changes the repressor molecule so that it cannot bind to the operon. What would be the result?
The operon would be turned on only if glucose is absent;
If the repressor can’t bind to the operon, then RNA polymerase (once it binds) can do transcription.
However, RNA polymerase cannot bind unless glucose is absent (thus allowing cAMP to bind to the activator)
Lactose (or allolactose) has what effect on the lac operon?
It keeps the repressor away from the operator;
Lactose (or allolactose) binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator, thereby allowing transcription of the lac operon.
What is the repressor?
A protein that binds to the operator region of the lac operon to inhibit transcription of the downstream genes when lactose is absent
What is the operator?
Where the repressor binds, controlling access of RNA polymerase to the promoter and thus regulating gene expression
What is the promoter?
Serves as the binding site for RNA polymerase, initiating the transcription of the adjacent structural genes in the operon
Why is this not correct?
The operator is the location where the RNA polymerase binds
The operator is where the repressor binds
While the RNA polymerase binds to the promoter region
What does the repressor do?
Prevents RNA polymerase from transcribing
Where does cAMP bind?
The activator site
The Activator site must be activated in order for RNA polymerase to _____
attach to the operon
What specific effect does glucose have on the lac operon?
It causes cAMP to be used up, thus preventing activation
What is cAMP?
Cyclic AMP (cAMP) is a second messenger molecule
In the lac operon, cAMP binds to the (CAP), enabling it to attach to the promoter region and enhance transcription of certain genes,
especially in the absence of glucose
In which situation would the lac operon be “turned on” (what is absent and what is present)?
Glucose absent and lactose present
What must occur to allow the transcription of genes in the lactose operon?
(what must bind to what)
The inducer must bind to the repressor
What is the inducer?
The inducer is a small molecule, such as lactose or allolactose, that binds to a repressor protein in the lac operon,
causing a conformational change that prevents the repressor from blocking transcription of the operon’s genes
You observe a microbiologist examining two plates and notice the pattern of colonies are nearly identical with the exception of a few colonies that are absent on one of them. The plates likely were produced by?
replica plating;
Replica plating is a technique used to transfer colonies from one agar plate to another, allowing for the comparison of growth patterns and the identification of colonies that may have different characteristics or mutations, such as those that are absent on one plate.
Define operon
The operator and promoter sites and structural genes they control
Define repression
The process by which a repressor protein can stop the synthesis of a protein
Define induction
The process that turns on the transcription of a gene
Describe promoter
The starting site on a DNA strand for transcription of RNA by RNA polymerase
Describe operator
The region of DNA adjacent to structural genes that controls their transcription
Describe repressor
A protein that binds to the operator site to prevent transcription
Describe gene expression
A segment of DNA (a sequence of nucleotides in DNA) encoding a functional product
Describe transcription
The process of synthesizing RNA from a DNA template
What is the difference between repressible operons and inducible operons.
repressible operons are inactive by default
and inducible operons are active by default
What relies on a molecule binding to the repressor to prevent the repressor from binding to the operator?
Induction;
For example, lactose is the inducer of the (inducible) lac operon. The presence of allolactose causes the expression of lactose-metabolizing enzymes. Allolactose does this by binding to the repressor protein and preventing it from binding to the operator sequence of the lac operon.
Bacteria are growing in an open protein shake you placed in the refrigerator three weeks ago. The shake’s ingredients include glycine and leucine—amino acids the bacteria are capable of synthesizing. The shake also contains sucrose and fructose—sugars the bacteria are capable of catabolizing. Assuming the gene expression necessary for all four of these functions is controlled by operons, what will happen to sucrose?
Sucrose will bind to the repressor, and the structural genes for catabolizing sucrose will be expressed;
Because fructose is present in the shake, the bacteria will use it as an energy source. This means the bacteria will express the genes for catabolizing it.
Pictured below is the inducible soap operon of the Pseudomonas species growing in the oncology ward. Imagine the operator has been damaged such that the active repressor no longer binds to it. How would this damage affect the growth of Pseudomonas?
Growth on soap would not change much, but the damage would decrease the species’ growth elsewhere;
damage of the operator would cause the soap-metabolizing enzymes to be expressed all the time. The species would still be able to grow on soap, but, growing elsewhere, the bacteria would waste resources by expressing these genes unnecessarily.
Order the correct sequence of events for the tryptophan repressible operon (6). The starting point is that tryptophan levels are low.
first - RNA polymerase binds to the promoter
second - structural genes are transcribed
third - translation of mRNAs occurs; proteins are produced
fourth - tryptophan levels increase
fifth - tryptophan binds to the repressor
sixth - repressor binds to the operator
