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33 Cards in this Set

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  • Back
DNA contains many different genes that are transcribed into different:
mRNAs, tRNAs, and rRNAs
An RNA molecule is:

a double helix
OR
usually single-stranded
usually single-stranded
An mRNA molecule is produced by ________.
transcription
Each codon calls for a specific:
amino acid
Anticodons pair with ______.
mRNA codons
______ are base sequences that must be removed before a pre-mRNA molecule can be translated.
introns
_______ are the parts that are still in the mRNA when it has translated into protein.
exons
Transcription is initiated at a _________.
promoter
What three key respects makes transcription different from DNA replication?
1. only ONE region of ONE DNA strand is used as a template.
2. instead of DNA polymerases, the type of enzyme known as RNA polymerase catalyzes nucleotide additions to a growing RNA strand.
3. at the end of transcription there is a single, free strand of RNA nucleotides, not a double helix
During gene transcription, adenine base-pairs with ______, and guanine with _______.
uracil
cytosine
_______ are the only molecules that carry protein-building instructions from DNA into the cytoplasm.
mRNAs
Ribosomes are composed of what 2 things?
rRNA and proteins
Each kind of tRNA has a(n) _______ that is complementary to an mRNA _______.
anticodon
codon
Enzymes, which can restrict bacteriophage growth in a host cell, are now called:
restriction enzymes
What is a genome?
all of the DNA in a haploid number of chromosomes for a species
Restriction enzymes cut DNA at a specific sequence.
What is the difference between blunt and sticky ends?
*sticky: a restriction fragment's single-stranded tail can base-pair w/ a complementary tail of any other DNA fragment or molecule cut by the same restriction enzyme = this will form a recombinant DNA molecule sealed by DNA ligase
*blunt:
ATGTCA
TACAGT (nothing hanging off)
What is a plasmid?
a very small circle of extra DNA that has just a few genes and that gets replicated along with the bacterial chromosome
Explain the process to make a DNA clone.
(before cell division, replication enzymes replicated the plasmid, so a cell can hold many identical copies of foreign DNA)
in research laboratories, foreign DNA typically is inserted into a plasmid for replication
-the outcome is a DNA clone, b/c bacterial cells have made many identical, "cloned" copies of it
A DNA strand "copied" from a mature mRNA transcript is called:
cDNA (complementary DNA)
______________ catalyzes transcription in reverse.
Explain.
Reverse transcriptase
-this enzyme from RNA viruses builds a complementary DNA strand on an mRNA transcript
-then other enzymes remove the RNA from the mRNA-cDNA molecule and substitute a complementary DNA strand
= the outcome is double-stranded cDNA
The polymerase chain reaction, widely known as PCR, is another way to _______ fragments of chromosomal DNA or cDNA
amplify
What are primers?
*used in polymerase chain reaction
-synthetic, short nucleotide sequences, ten to 30 or so nucleotides long, that can base-pair w/ complementary sequences in DNA
-DNA polymerases recognize them as START tags
Explain the PCR process. (amplifying DNA)
*at the beginning of each temperature cycle, the 2 strands of all molecules of DNA in the mixture unwind from each other
*primers become positioned on exposed nucleotides at targeted sites according to base-pairing rules
-DNA polymerases recognize the primers as START tags and assemble complementary sequences on the strands = this doubles the number of identical DNA fragments
PCR is far more rapid than ________ _________.
cloning methods
What do researchers use now to learn the sequence of cloned DNA or PCR-amplified DNA in only a few hours?
automated DNA sequencing
Standard nucleotides include dATP, dTTP, dCTP, and dGTP.
What is the importance of the modified versions of nucleotides in automated DNA sequencing?
represented as T*, C*, A*, and G*
*ddNTP = dideoxydNTP = no 3'-OH which his required to have for DNA polymerase
-each modified version is labeled with a molecule that fluoresces a certain color when it passes through a laser beam
-every time one of these modified nucleotides get incorporated into a growing DNA strand, it arrests DNA synthesis
After the primer binds with its complementary sequence, DNA polymerase synthesizes a new DNA strand. Suppose the polymerase encounters a T in a DNA template strand. What 2 things might happen?
-it will catalyze the base-pairing of either A or A* to it
*if A is added to the new strand, replication will continue
*if A* is added to the new strand, replication will stop; the modified nucleotide will block addition of any more nucleotides to that strand
Because either a standard or a modified nucleotide could be added at every exposed base, the new strands end at _________ locations in the sequence.
different
What is the role of the automated DNA sequencer?
*separates the sets of fragments by gel electrophoresis
-b/c the fragments all have a modified nucleotide at the 3' end, each set fluoresces a certain color as it passes through a laser beam
-automated sequencer detects the color and indicates which nucleotide is on the end of the fragments in each set
-it assembles the information from all nucleotides in the sample, and in this way it reveals the entire DNA sequence
A mixed collection of bacteria that contain different cloned DNA fragments is called:
a gene library
-used when you want to isolate a gene from all others in a genome
What is a probe?
a very short stretch of DNA labeled with a radioisotope so that it can be distinguished from other DNA molecules in a given sample
-part of the probe must be able to base-pair with some portion of the gene of interest
Any base-pairing that takes place between sequences of DNA (or RNA) from different sources is called:
nucleic acid hybridization
What are the 5 steps for the screening for genes?
1.Grow the bacterial colonies on suitable medium in a petri plate.
2.Place a nylon filter over the colonies and lift some cells off.
3.Place the filter in a solution to disrupt the cells but leave DNA sticking to the filter.
4.Add a radioactively-labeled probe DNA to the filter where it will bind to the DNA fragments of complementary sequence.
5.Expose the filter to x-ray film to locate the gene of interest, which will be in the same location as the cells in the petri plate.