Chapter 17 Flashcards
gene expression
the process by which DNA directs protein synthesis, two stages: transcription and translation
information content of DNA is in the form of _____ _____ of _____
specific sequences of nucleotides
The DNA inherited by an organism leads to specific traits by….
dictating the synthesis of proteins
RNA is the bridge between ____ and ____ for which they code
genes and proteins
transcription
the synthesis of RNA under the direction of DNA
Translation
the synthesis of a polypeptide using information in the mRNA
Ribosomes
the sites of translation
in a eukaryotic cell, the nuclear envelope separates _____ from _____
transcription and translation
in prokaryotes, _____ of mRNA can begin before ____ has finished
translation
transcription
primary transcript
the initial RNA transcript from any gene prior to processing
central dogma
the concept that cells are governed by a cellular chain of command: DNA -> RNA -> protein
how many amino acids are there?
20
how many necleotide bases are in DNA
4
triplet code
a series of nonoverlapping, three-nucleotide words… the flow of information from gene to protein is based on these triplet codes
The words of a gene are transcribed into complementary nonoverlaping three-nucleotide of words of ____
—these words are then translated into a chain of ____ ___, forming a polypeptide
mRNA
amino acids
template strand
- happens during transcription
- provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
- **the template strand is always the same strand for a given gene
codons
during translation, the mRNA base triplets are codons (read in the 5’ to 3’ direction)
each codon specifies the ____ _____ to be placed at the corresponding position along a polypeptide
amino acid
how many triplets signal for “stop” to end translation
3 triplets
true or false:
genetic code is nearly universal, shared by the simplest bacteria to the most complex animals
true
what is the first stage of gene expression
transcription
RNA polymerase
RNA synthesis is catalzyed by RNA polymerase which pries the DNA strands apart and hooks together the RNA nucleotides
- RNA is complementary to the DNA template
- RNA synthesis follows same base pairing other than thymine is now uracil
promoter
the DNA sequence where RNA polymerase attaches
terminator
the sequence signaling the end of transcription
transcription unit
the stretch of DNA that is transcribed
what are the three stages of transcription
- initiation
- elongation
- termination
start point (transcription in eukaryotic cells)
promoters signal this trancriptional start point and usually extend several dozen nucleotide pairs upstream of the start point
transcription factors
transcription in eukaryotic cells
mediate the binding of RNA polymerase and the initiation of transcription
Transcription initiation complex
transcription in eukaryotic cells
the completed assembly of transcription factors and RNA polymerase bound to a promoter…this is transcription initiation complex
TATA box
transcription in eukaryotic cells
a promoter.. crucial in forming the initiation complex in eukaryotes
in transcription the RNA polymerase moves along the DNA, it ____ the double helix
untwists
nucleotides are added to the _’ end of the growing RNA molecule in transcription
3’
how does termination work in bacteria versus eukaryotic
bacteria: stops transcription at the end of the terminator and mRNA can be translated without further modification
eukaryotes: RNA polymerase transcribes the polyadenylation signal sequence; The RNA transcript is released 10-35 nucleotides past this polyadenylation sequence
what do eukaryotic cells do the RNA after transcription?
- enzymes in eukaryotic nucleus modify pre-mRNA before the genetic messages are dispatched to the cytoplasm
- During RNA processing, both ends of the primary transcript are altered
- some interior parts of the molecule are cut out, and others are spliced together
what does the 5’ end get in mRNA
what does the 3’ end get in mRNA
- 5’ cap
- 3’ poly- A tail
what is the functions of these 5’ and 3’ ends
- facilitate export of mRNA
- protect mRNA from hydrolytic enzymes
- help ribosomes attach to the 5’ end
introns
regions that are taken out and will not be expressed
exons
regions that are eventually expressed and translated into amino acid sequence
RNA splicing
removes introns and joins exons, creating mRNA molecule
what carries out RNA splicing
splicesomes
ribozymes
catalytic RNA molecules that function as enzymes and can splice RNA
what are the three properties of RNA enabling it to function as an enzyme
– It can form a three-dimensional structure because
of its ability to base-pair with itself
– Some bases in RNA contain functional groups that may participate in catalysis
– RNA may hydrogen-bond with other nucleic acid molecules
domains
- proteins have a modular architecture consisting of descrete regions called domains
- different exons code fro the different domains in a protein
genetic information flows from ____ to ___ through the process of translation
- mRNA
- protein
- Translation
transfer RNA
a cell translates an mRNA message into protein “language”
–tRNA transfer amino acids to the growing polypeptide in a ribosome
anticodon
the anticodon base-pairs with a complementary codon on mRNA
accurate translation requires what two steps
First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase
– Second: a correct match between the tRNA anticodon and an mRNA codon
wobble
flexible pairing at the third base of a codon is wobble. allows some tRNAs to bind to more than one codon
ribosomes
-facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
what are the two ribosomal subunits made up of?
proteins and ribosomal RNA
what are the ribosomes three binding sites?
P site
A site
E site
what is P site?
holds the tRNA that carries the growing polypeptide chain
what is A site?
holds the tRNA that carries the next amino acid to be added on the chain
what is E site?
the exit site, where discharged tRNAs leave the ribosome
what does the initiation stage of translation do?
brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
1st: a small ribosomal subunit binds with mRNA and a special initiator tRNA
2nd: the small subunit moves along the mRNA until it reaches the start codon (AUG)
3rd: proteins called initiation factors bring in the large subunit that completes the translation initiation complex
what does the elongation stage of translation do?
- amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain
- each addition involves proteins called elongation factors and occurs in three steps (1) codon recognition (2) peptide bond formation (3) translocation
- translation proceeds along the mRNA in a 5’ to 3’ direction
what happens in the termination stage of translation
- a stop codon in the mRNA reaches the A site of the ribosome
- A site accepts a protein called a release factor
- release factor causes the addition of a water molecule instead of an amino acid
- this reaction releases the polypeptide, and translation assembly falls apart
polyribosome
a number of ribosomes that can translate a single mRNA simultaneously
during and after synthesis, a polypeptide chain spontaneously ___ and ____ into a _____ ____
- coils
- folds
- 3D shape
signal peptide
polypeptides destined for the ER or for secretion are marked by a signal peptide
SRP (signal recognition particle)
binds to the signal peptide
-the SRP brings the singal peptide and its ribosome to the ER
point mutations
chemical changes in just one base pair of a gene
what two general categories are there for point mutations
- nucleotide pair substitutions
- one or more nucleotide pair insertions or deletions
nucleotide pair substitution
replaces one nucleotide and its partner with another pair of nucleotides
silent mutations
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
missense mutations
still code for an amino acid, but not the correct one
nonsense mutations
change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
frameshift mutation
caused by insertions or deletions of nucleotide pairs
mutagens
physical or chemical agents that can cause mutations
