Chapter 16,17 Flashcards
what is a mutation?
heritable, permanent change in a gene that changes genotype and creates new alleles
what is a mutant?
an individual that carries a mutation
what are null/loss-of-function alleles?
allels that do not function at all
one-gene, one-enzyme hypothesis
each gene contains the info needed to make an enzyme
RNA molecules act as a ___ between genes in the nucleus and protein making structures outside nucleus in cytoplasm
link
what does mRNA do?
carries info out of nucleus from DNA to site of protein synthesis
what does RNA ploymerase do?
enzyme that could use DNA as a template strand to synthesize a complementary RNA molecule
how is RNA poly. different from DNA poly.?
RNA poly. does not need a RNA primer to initiate RNA synthesis
what is the central dogma of molecular biology?
summarizes the flow of information in cells; states that DNA codes for RNA, which codes for proteins
in order for DNA molecules to make proteins, what three processes need to occur?
DNA replication, RNA synthesis/transcription, Protein synthesis/translation
An organism’s genotype is determined by:
the sequence of bases in its DNA
what are alleles?
particular forms of a gene
many genes code for RNA molecules that do not function as mRNAs, transcribed from DNA but never translated into proteins. Why?
some of these RNAs from parts of ribosomes (ribosomal RNA) or help bring nucleotides towards mRNAs and ribosomes (transfer RNA)
what is a codon?
group of three bases that specifies a particular amino acid
what is a start codon?
AUG, signals protein synthesis should start at that point, specifies methionine
what is a stop codon?
UAA,UAG,UGA, don’t code for any amino acids but signal end of translation
what are properties of the genetic code?
redundant - all amino acids except methionine and tryptophan are coded for by more than one codon
unambiguous - a given codon never codes for more than one amino acid
non-overlapping - Once the ribosome locks onto the first codon, the reading frame is established, and the ribosome then reads each separate codon one after another.
universal - all codons specify same amino acids in all organisms
conservative - when several codons specify same amino acid. first two bases are usually identical
why is genetic code being conservative important?
less likely to alter amino acid if a change in DNA sequence leads to a change in the third position of a codon
what is a base-pair substitution mutation
base pair is substituted by another one
what is a point substitution?
mutations that alter/change one or a few adjacent base pairs
what happens when a point mutation occurs in a region of DNA that codes for proteins?
it may change the amino acid coded
what is a missense mutation?
when a mutation leads to an incorrect amino acid being coded
what is a silent mutation?
a point substitution that does not change the amino acid sequence, usually neutral
what is a nonsense mutation?
a point substitution that changes the amino acid codon into a stop codon, usually harmful
what is a stop codon readthrough?
very rare mutation that changes a normal stop codon into a normal amino acid codon
what is a reading frame?
the sequence of codons in an mRNA
what would happen if a mutation added or removed base pairs from DNA?
mRNA would have absent or extra nucleotides, throwing sequence of codons out of register and alter meaning of subsequent codons
what are frameshift mutations?
mutations also called insertion-deletion mutations because of the change they make in a DNA and disrupt reading frame of RNA, almost always harmful
how are some mutations beneficial?
some mutations increase fitness of an organism
how are some mutations neutral?
if mutation has no effect on fitness or its ability to survive and reproduce, ex. silent mutations
how are mutations harmful?
mutations that lower fitness depending on environment
what happens if mutations occur in DNA sequences that don’t code for proteins?
not referred to as missense, nonsense, silent, frameshift, etc. because these terms only apply to protein-coding gene areas
what do changes in chromosome number result from?
mistakes in moving chromosomes into daughter cells during meiosis and mitosis
what is polyploidy?
state of having more than two of each type of chromosome
what is aneuploidy?
addition or deletion of individual chromosomes
mutations producing polyploidy and aneuploidy don’t change DNA sequences but do cause permanent change in an organism’s DNA by altering the number of copies in each sequence
what is chromosome inversion?
segments in chromosome are flipped and rejoined
what is chromosome translocation?
parts of chromosomes are attached to different chromosomes
what are chromosome deletions?
loss of a segment of chromosomes?
what is chromosome duplication?
presence of one or more additional copies of a segment
what is a karyogram and a karyotype?
karyotypes are written description of a person’s chromosomes and a karyogram is a visual representation of a person’s chromosomes
what is the coding strand?
the non-template strand with a sequence matching the RNA sequence that codes for a polypeptide
Bacteria have how many RNA polymerase?
one
how many types of RNA polymerases do eukaryotes have?
at least three distinct types - RNA poly I, II, and III, each only producing certain types of RNA
what is the sigma protein?
binds to RNA polymerase before transcription can begin, forming a holoenzyme
what can the sigma protein do?
can bind to any sequence of DNA
what is a holoenzyme?
“whole enzyme” consists of a core RNA polymerase containing active site for catalysis and other required proteins such as the sigma protein
what are promoters?
regions of DNA that promote start of transcription
why do most bacteria have alternative sigma proteins that bind to promoters with different DNA base sequences?
allows organism to activate certain genes in response to environmental changes
why is reaction catalyzed by RNA polymerase exergonic and spontaneous?
NTPS have significant potential energy due to their three phosphate groups
explain the process of initiation of transcription
- Initiation begins when sigma binds to promoter region of DNA
- Initiation continues when RNA poly. opens DNA helix and transcription begins
- Initiation is complete when sigma releases form promoter, RNA synthesis continues from DNA
what is the elongation phase of transcription?
RNA polymerase catalyzes addition of nucleotides to the 3’ end of growing RNA at the rate of 50 nucleotides per second
what is the termination phase of transcription?
transcription stops when RNA polymerase transcribes a DNA sequence called a transcription-termination signal that when trancribed rapidly folds back on itself to form a hairpin/doublehelix held together by complementary base pairing, resulting in separation of enzyme and its product
describe the ending transcription process
- hairpin forms when RNA poly. transcribes a transcription-termination signal
- termination when RNA hairpin causes RNA to separate from RNA polymerase
what is the TATA box?
eukaryotic promoters centred about 30 base pairs upstream of transcription start site
what are basal transcription factors?
eukaryotic equivalent of sigma proteins, assembles at promoter and RNA polymerase follows
what is the poly(A) or polyadenylation signal?
termination of eukaryotic protein-coding genes that when copied into RNA, an enzyme binds to it and cuts RNA 10-35 nucleotides downstream, releasing RNA from enzyme
where does transcription occur in eukaryotes?
nucleus
where does translation occur in eukaryotes?
by using ribosomes location in cytoplasm
what is a primary transcript?
RNA molecule produced when a gene is transcribed
what is RNA processing?
some primary transcripts are ready to function but most need to be modified first, RNA processing is general term form any changes needed to convert a primary transcript into a mature RNA
what are pre-mRNAs?
primary transcripts that undergo dramatic changes to distinguish them from mature mRNAs they will become
what are exons?
regions of eukaryotic genes that are part of the final RNA (exons are “ex”pressed)
what are introns?
regions of eukaryotic genes not in the final RNA (introns “inter”vene)
why are eukaryotic genes much longer than their corresponding mature RNAs?
because of introns that do not make it to final mature RNAs
what is RNA splicing?
where RNA is spliced, introns removed from growing RNA strand and remaining exon segments are joined
where does RNA splicing occur?
within the nucleus while transcription is still underway
splicing is performed by what?
a very large complex called a spliceosome made up of proteins and RNAs
why are RNAs found in spliceosome called snRNAs?
because these RNAS function in the nucleus
what do you call snRNAs that join with proteins?
small nuclear ribonucleoproteins or snRNPs
what is the process of intron removal
- snRNPs bind to start of intron and near intron end at an adenine ribonucleotide (key A base) as pre-mRNA emerges from RNA poly.
- snRNPS assemble to form spliceosome
- 5’ end of Intron is cut and loop/lariat forms with adenine at its connecting point
- 3’ end of intron cut, intron as a lariat is released, exons join together by phosphodiester bond, excised intron degrades into individual nucleotides
what is the 5’ cap?
as soon as the 5’ end of a pre-mRNA emerges, enzymes add the cap consisting of a modified guanine nucleotide with three phosphate groups, enabling ribosome to bind to mRNA and protects 5’ end from degrading
what is the polyA tail?
when an enzyme cleaves 3’ end of pre m-RNA signal downstream of polyA signal, an enzyme adds long row of 100-250 adenine nucleotides which is needed for ribosomes to start translation and to protect 3’ end from degrading
mRNAs in bacterial cells are rarely processed
no introns or 5’ caps or polyA tails
what are the untranslated regions in a mature mRNA?
UTRs help stabilize mature RNA and regulate its translation
only the middle of the mRNA carries info to make a protein
mRNAs in bacteria also possess untranslated regions but are relatively smaller
which arm in chromosome is biggr? P or Q?
Q; P arm stands for “petit”
what is the polymerase chain reaction?
PCR is a common method of making copies of a piece of DNA, allows specific DNA region to be replicated/amplified into many copies
What are components required for PCR?
template DNA strand,
DNA nucleotides,
DNA polymerase,
DNA primer
what is denaturation?
DNA is heated 95C to separate into two single strands, hydrogen bonds broken but not covalent and phosphodiester bond
what is annealing?
PCR solution is cooled to 50-60C, primers anneal to complementary sequences on DNA template strands
what is extension?
DNA poly. synthesizes new DNA strands by extending primers at 72C
Does PCR result in Okazaki fragments?
no
what does in vitro mean?
in “glass”
what does in vivo mean?
in cell, in body, in life
After n cycles of amplification there are 2^n copies of template sequence
what is gel electrophoresis?
determines size of DNA fragments, determines whether or not you successfully amplified DNA via PCR
how does gel electrophoresis work?
an electrical current passes through a gel with a negative pole at one end and a positive pole at another
Where do DNA fragments move in gel electrophoresis?
DNA fragments move toward positive pole according to size because of DNA being negatively charged
DO smaller or larger fragments move further down gel?
smaller fragments move faster while larger ones move more slowly
what are restriction enzymes?
class of enzymes that can recognize and cleave specific sequences in DNA
what does recombinant DNA technology do?
recombines DNA molecules from two or more different sources into a single molecule
what is transformation in recombinant DNA technology?
recombinant DNA is introduced into a bacterial cell, in which bacteria are chemically induced to take up DNA from outside cell, as bacteria cell divides it also replicates recombinant DNA
what is CRISPR?
editing DNA in vivo using protein Cas9 and complimentary CRISPR RNA to target and cleavage genomic DNA, resulting in being able to alter cut DNA
why is RNA more reactive than DNA?
single stranded, has extra OH group, 5’ has triphosphate
why did RNA probably precede DNA?
both are information molecules but RNA can form complex secondary structures and has enzymatic functions, used in key cellular processes such as transcription and translation
what are mutagens?
chemicals that increase mutation probability
why would mistakes in transcription/translation not be as serious compared to replication?
DNA/source material is not affected
is RNA heritable?
no, unstable and will not be passed down
in which ways can mutations affect proteins?
structure, function, protein’s level of expression, protein’s timing of expression, protein’s frequency of expression
is the insertion/deletion of 3 bases a frameshift?
No
what are transposons?
transposable elements are DNA sequences that can move from one position to another in a genome, inserts itself into a gene and disrupts its function
in eukaryotes, the initiation of transcription requires:
general transcription factors to bind to promoters,
transcriptional activator proteins to bind to enhancer sequences
