Chapter 17 Flashcards
What is gene expression?
a process in which DNA directs the synthesis of proteins
What is the one gene-one enzyme hypothesis?
a gene dictates the production of a specific enzyme
What is the one gene-one polypeptide hypothesis? (2)
Some proteins are not enzymes
Some proteins are made up of multiple polypeptides with different genes
What is transcription? (3)
Synthesis of RNA using the information in the DNA
Two nucleic acids are written in different forms of the same language
Information is transcribed from DNA to RNA
Messenger RNA
Carries a genetic message from the DNA to the protein-syntehsizing machinery of the cell
What is translation? (2)
Synthesis of polypeptides using the information in the mRNA
Cell must translate the nucleotide sequence of an mRNA into the amino acid sequence of a polypeptide
What are ribosomes? (2)
sites of translation
facilitates the orderly linking of amino acids into polypeptide chains
Bacteria vs Eukaryote gene expression (3)
Bacterial DNA is not separated by nuclear membranes from ribosomes
allows translation and transcription to occur at the same time
eukaryotic cells transcript first in the nucleus, transport into the cytoplasm where it translates
What is pre-mRNA?
RNA transcripts that are modified into mRNA
What is primary transcript?
Initial transcript from any gene that is not translated into a protein
What is the triplet flow? (4)
genetic instructions for a polypeptide chain are written in the DNA as a series of three-nucleotide words
series of nucleotides is transcribed into three specific orders, which is then translated
gene determines the sequence of nucleotide bases along the length of the RNA being synthesizes
for each gene, only one strand of DNA is transcribed
What is the template strand? (3)
DNA strand being transcribed
the same strand is used as the template every time for a given gene
synthesized in an antiparallel direction to the template strand
What are codons?
mRNA nucleotide triplet written in teh 5’ > 3’ direction
Coding strand (2)
non-template strand is identical to codons but with T instead of YOU
during translation, it is read in the 5’ > 3’ direction
What are codons for? (5)
64 exists
61 of them are designated for amino acids
3 are termination codons
AUG acts as a start signal and codes for methionine
enzymes can remove methionine
What is the reading frame?
Correct groupings of symbols for an intended language
What are the stages of transcription?
Initiation, elongation, and termination
What is RNA polymerase? (4)
An enzyme that pries two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand
Bacteria have one type
Eukayrotes have at least three
do not need primers
What is a promoter?
DNA sequence where RNA polymerase attaches and initiates transcription
What is a terminator?
A squence that signals the end of transcription
What is a transcription unit?
A stretch fo DNA downstream from the promoter that is transcribed into an RNA molecule
What is the start point?
The nucleotide where RNA synthesis begins
What is the transcription factor? (3)
Mediates the binding of RNA polymerase and the initiation of transcription
after transcription factors attach to the promoter, the RNA polymerase 2 binds to it
forms the transcription initiaition complex
TATA box (2)
nucleotide sequence containing TATA upstream around 25 nucleotides from the start point
once the transcription factors bind to the TATA box, polymerase can bind to it
Elongation process
When the RNA polymerase moves along the DNA, and the new RNA molecule peels away
Termination in Bacteria (2)
Transcription proceeds through a terminator sequence in the DNA
terminator functions as the termination signal, requiring no further modification before translation
Termination in eukaryotes (4)
Transcribes a polyadenylation signal (AAUAA) in the pre-mRNA
once it appears, it is immediately bound by certain proteins in the nucleus
proteins cut it free from the polymerase, releasing the pre-mRNA
RNA polymerase continues to transcribe until enzymes catch up and dissociates it
What is RNA processing? (2)
Enzymes in the eukaryotic nucleus modify pre-mRNA in specific ways before genetic message I dispatched to the cytoplasm
both ends are altered and some inner sections are cut out
How is mRNA altered? (2)
5’ end receives a 5’ cap, a modified form of guanine added to the first 20-40 nucleotide
3’ end adds adenine to form a poly-A tail
What is the mRNA ends for? (30
Facilitate export of the mature mRNA from the nucleus
helps protect the mRNA from degradation by hydrolytic enzymes
helps ribosomes attach to the 5’ end of mRNA
What is RNA splicing?
Removal of large portions of the RNA moleculues
What are introns?
Noncoding segments of nucleic acid that lie between coding regions
What are exons?
epxressed regions of the nucleic acids
What is UTR
Part of the mRNA that will not be translated but help ribosome binding
How does RNA get spliced?
Introns get cut out and exons get joined together
What are spliceosomes?
A complex of proteins and small RNA that removes introns
What are ribozymes?
RNA molecules that function as enzymes
introns can function as ribozymes, catalyzing its own excision
How can RNA enable some RNA molecules to function as enzymes? (3)
Because it is single-stranded, a region of an RNA molecule may base-pair in an antiparallel arrangement with a complementary region elsewhere, forming a 3d structure like an enzyme
Some of the bases in RNA contain functional groups that can participate in catalysis
ability of RNA to hydrogen bond with other nucleic acid molecules add specificity to its catalytic activity
Why are introns important? (3)
A single gene can encode more than one kind of polypeptide
depends on which segments are treated as exons (alternative RNA splicing)
allows humans to work with small numbers of genes
What are domains? (3)
Discrete structural and functional regions of proteins
one domain can act as an active site, while another binds to a cellular membrane
different exons code for different domains
What is exon shuffling?
Introns can facilitate the evolution of new and potentially beneficial proteins
What is transfer RNA (tRNA)?
Translator that reads a series of codons along an mRNA molecule and transfers amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome
What are ribosomes? (2)
Structures made of proteins and RNA
Adds each amino acid brought to it by tRNA to the growing end of a polypeptide chain
How is tRNA used in translation? (5)
Reads a nucleic word (the mRNA codon) and interprets it as a protein word (the amino acids)
bears a specific amino acid at one end
bears a nucleotide triplet that can base-pair with the complementary codon on mRNA
consists of a single RNA strand, smaller than mRNA
Can fold itself and form a 3d structure, and twists into an L shape
What is an anticodon? (4)
A nucleotide triplet that base-pairs to a specific mRNA codon
example- mRNA codon 5’-GGC-3’ (code for glycine)
tRNA base-pairs with 3’-CCG-5’ as its anticodon
carries glycine at the other end
Where is tRNA transcribed? (3)
From DNA templates
made in the. nucleus and travels to the cytoplasm
used repeatedly
What is molecular recognition?
tRNA that binds to an mRNA codon must carry that amino acid, carried out by aminoacyl-tRNA synthetases
Pairing of tRNA anticodon with the appropriate mRNA codon
some tRNA are able to bind to more than one codon
What are aminoacyl0tRNA synthetases? (2)
Enzyme that only fits a specific combination of amino acid and tRNA
catalyzes covalent attachment of amino acid to its tRNA
What is wobble? (2)
flexible base pairing at specific codon positions
YOU at the 5’ end of tRNA can pair with A or G in the 3’ end
What are ribosomes used for? (2)
facilitates the specific coupling of tRNA anticodons with mRNA codons during protein synthesis
Holds the tRNA and mRNA close together and catalyzes the formation of peptide bonds
What are ribosomes made up of? (2)
A large and small subunit that joins when attached to an mRNA molecule
subunits are made up of ribosomal RNA
1/3 is made up of proteins found in the exterior
Ribosomal RNA (2)
made in the nucleolus
most abundant type of RNA
What do proteins on ribosomes do?
Support shape changes
How do bacterial and eukaryotic ribosomes differ? (2)
Eukaryotic ribosomes are larger
some drugs can inactivate bacterial ribosomes without affecting eukaryotic ribosomes
What is the ribosome structure? (2)
a binding site for mRNA and three sites for tRNA
an exit site in the large subunit where the polypeptide leaves
What are the three binding sites for tRNA in ribosomes?
P site holds the tRNA carrying the growing polypeptide chain
A site holds the tRNA carrying the next amino acid after the P site
E site is where discharged tRNA leaves the ribosomes
What occurs during translation initiation?
mRNA, tRNA with the first amino acid, and subunits come together
ribosomal subunit binds to both mRNA and a specific initiator tRNA (carries methionine)
How does the translation stage differ in eukaryotes?
small subunits is bound to the tRNA and binds to the 5’ cap f mRNA. Moves downstream until it reaches the start codon
What is the translation initiation complex? (2)
union of all the RNA and ribosomes
formed by GTP hydrolysis
What are initiation factors?
proteins required to bring all the components together
What occurs during translation elongtaion?
Amino acids are added one by one
codon recognition occurs
peptide bond formation occurs
translocation occurs
What is codon recognition? (2)
Anticodon of an incoming tRNA pairs with the complementary mRNA in the A site
GTP increases accuracy and efficiency
What is peptide bond formation? (2)
rRNA in the large subunit catalyzes formation of a peptide bond between amino groups of the A site and P site
removes polypeptide from the tRNA in the P site
What is translocation?
ribosomes translocates the tRNA in the A site to the P site, P site to the E site where it is removed
What occurs during termination translation? (3)
When ribosomes reach a stop codon on mRNA, A site accepts a release factor
release factor promotes hydrolysis of the bond between the tRNA in the P site and the last amino acid of the polypeptide
two ribosomal subunits and other components dissociate
How do proteins fold?
gene determines primary structure, folding proteins
What is post translational modification? (3)
certain amino acids being chemically modified by the addition of sugars, lipids, phosphate groups, and more
enzymes removes amino acids from the leading end
can also cleave
What is the difference between free and bound ribosomes? (2)
Free ribosomes synthesize proteins that stay in the cytosol
bound ribosomes are attached to the ER< and makes proteins of the endomembrane system and proteins secreted from the cell
How are polypeptides synthesized? (9)
Growing polypeptide either completes in the cytosol or cues the ribosome to attach to the ER
Polypeptides for attached RNA are marked by signal peptide
Recognized by a signal-recognition particle (SRP)
SRP brings the ribosome to a receptor protein built into the ER Membrane
SRP then binds to a receptor protein in the ER
forms a protein complex that forms a pore and ahs a signal-cleaving enzyme
SRP leaves, polypeptide synthesis resumes, and translocates across the membrane
signal cleaving enzymes cuts off the signal peptide
rest of the completed polypeptide leaves the ribosome and fold into its final conformation
How are signal proteins for organelles apart from the endomembrane system formed?
Translation is completed in the cytosol before being imported to said organelles
How are multiple polypeptides made? (3)
Multiple ribosomes translate an mRNA at the same time
a single mRNA can be used to simultaneously make many copies (forms polyribosomes/ polysomes)
What is a mutation? (2)
Changes to the genetic information of a cell
responsible for the diversity of genes
What is point mutation? (2)
changes in a single nucleotide pairs of a gene
if it occurs in the gamete, it may be transmitted to offspring and future generation
What is a genetic disorder? (2)
a point mutation producing an adverse effect
example- sickle cell disease
What is nucleotide-pair substitution? (2)
Replacement of one nucleotide and its partner with another pair of nucleotides
some can have no effect due to the redundancy of genetic code
What is silent mutation? (2)
Mutation with no observable effect on phenotype
example- change in nucleotide pair changes codon but translates into the same amino acids
Missense mutation
substitutions that changes one amino acid to anther
What is nonsense mutation? (2)
mutation that changes a codon for an amino acid into a stop codon
terminates translation prematurely and produces a short polypeptide
What is an insertion?
Additions of nucleotide pairs in a gene
What is a deletion?
Loss of nucleotide pairs in a gnene
What is the consequence of deletion and insertions? (2)
Bothe produces a more disastrous effect compared to substitution
may alter the reading frame of the genetic message
What is a frameshift mutation? (2)
whenever the number of nucleotides inserted or deleted is not a multiple of three
all downstream nucleotides are improperly grouped
What is spontaneous mutation?
When a mismatched nucleotide strand is used as a template in the next round of replciation
What is a mutagen? (2)
Interacts with DNA and causes mutation
example- radiation
What are chemical mutagens? (3)
Can be similar to DNA nucleotide, pairs incorrectly
can interfere with correct DNA replication and distorts the DNA double helix
can change pairing properties of bases
What is a gene?
a region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule
