Chapter 17 From Gene to Protien Flashcards
What is transcription?
DNA to RNA
What is translation?
Uses mRNA to make a polypeptide from nucleotide form
Who First suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions
He thought symptoms of an inherited disease reflect and inability to synthesize the certain enzymes
Ex: alkaptonuriq
Archibald Garrod
Who studied mutants in bread mold and
They developed a “one gene-one enzyme” hypothesis,which states that each gene dictates production of a specific enzyme
Beadle and Tatum
How did Beadle and Tatums hypothesis change?
Started as “one gene – one enzyme”….
One gene-one protein…
One gene- one polypeptide…
Some genes code for RNA molecules
______________ is the synthesis of RNA under the direction of DNA
Transcription
Transcription produces…
Messenger RNA mRNA
____________ Is the synthesis of a polypeptide, which occurs under the direction of mRNA
Translation
Where is the site of translation?
Ribosomes
Cells are governed by a cellular chain of command:
DNA to RNA to polypeptides
Which strand is transcribed?
The template strand
Transcription is also in what direction?
5’- 3’
A gene is a region of DNA whose final product is either a ____________ or an ____________ molecule
Polypeptide, RNA
In what type of cell is The mRNA that is produced by transcription immediately translated without more processing?
Prokaryotic
In eukaryotic cells the ___________ separates transcription from translation
Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA
Nuclear envelope
RNA synthesis is catalyzed by ___________________, which pries the DNA strand apart and hooks together the RNA nucleotides
RNA polymerase
RNA synthesis follows the same base pairing rules as DNA, except __________ substitutes for __________
Uracil, thymine
The DNA sequence where RNA polymerase attaches is called the ______________; in prokaryotes the sequence signaling the end of transcription is called the __________
Promoter, terminator
The structure of DNA that is transcribed is called a….
Transcription unit
Bacteria don’t have Introns true or false?
True
What are the three stages of transcription?
Initiation (promoter), elongation, termination
The promoter is before the…..
Start site
Is the promoter transcribed?
No
What signals the initiation of RNA synthesis?
Promoter
_____________ mediate the binding of RNA polymerase and initiation of transcription
Recognizes for it to be on or off
If it is not there it will not be transcribed
Transcription factors
Completed assembly of transcription factors and RNA polymerase two bound to a promoter
Transcription initiation complex
Promoter sequence crucial in forming the initiation complex in many eukaryotic promoters
TATA box
- as RNA polymerase moves along the DNA, it on twist the double helix, 10 to 20 bases at a time
- transcription progresses at a rate of 60 nucleotides per second in eukaryotes
- A gene can be to transcribe simultaneously by several RNA polymerases
Elongation of the RNA strand
How is termination different in prokaryotes and eukaryotes?
In prokaryotes the polymerase stops transcription at the end of the terminator
10 to 35 nucleotides downstream of polyadenlyation signal (AAUAAA) RNA transcript is cut free from the polymerase
Enzymes in the eukaryotic nucleus modify pre-mRNA before the genetic messages are dispatch to the cytoplasm
during _____________, both ends of the primary transcript are usually altered
Also, usually some interior parts of a molecule are cut out, and the other parts splice together
RNA processing
Each end of a pre-mRNA molecule is modified in a particular way:
the 5’ end receives…..
The 3’ end gets….
These modifications share what functions?
A modified nucleotide cap
Poly-A tail
Seem to facilitate the export of mRNA
Protect mRNA from hydrolytic enzymes
Help ribosomes attached to the five prime end
*this is in eukaryotic cells
______________ removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
RNA splicing
In some cases, RNA splicing is carried out by…
Spliceosomes
- variety of proteins
- several small nuclear ribonucleoprotein (snRNPs) that recognize the spice sites
Spliceosomes
When RNA is enzymatic it is called?
Ribozyme
Function as enzymes and can spice RNA
Catalytic RNA molecules
Ribozyme
- some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing
- because of this The number of different proteins in organism can produce is much greater than its number of genes
- such variations are called….
Alternative RNA splicing
In many cases different _______ code for the different domains in a protein
Exons
How many potential codon combinations are there?
64
___________ on tRNA matched to __________ on mRNA
Anticodons
Codons
- a series of non-overlapping, three nucleotide words
- smallest unit that can code for all the amino acids
*nonoverlapping
Triplet code
Genetic code is __________ but not ambiguous
Redundant
- only the first two nucleotides are required to encode the correct amino acid
- The third nucleotide does not change it sense
- permits some variation or mutation without altering the message
Wobble
AUG encodes….
Methionine *start codon
A cell translates an mRNA message into protein with the help of….
Transfer RNA (tRNA)
Molecules of tRNA are not ___________. Each carries a specific amino acid on one end.
-each has an anti-codon on the other end, the anti-codon base pairs with a complementary codon on mRNA
Identical
-Single RNA strand that is only about 80 nucleotides long
-complementary stretches of bases hydrogen
Twist and folds into a three dimensional molecule
tRNA molecule
What are the two steps for accurate translation?
- First step, a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase
- Second step, a correct match between the tRNA anti-codon and an mRNA codon
- facilitate specific coupling of tRNA anti-codons with mRNA codons in proteins synthesis
- two ribosomal subunits are made of proteins and ribosomal RNA (rRNA)
Ribosomes
What are the three binding sites for tRNA?
- the P site holds the tRNA that carries the growing polypeptide chain
- the A site holds the tRNA that carries the next amino acid to be carried to the chain
- The E site is the exit site, where discharged tRNAs leave the ribosome
The three stages of translation…
All three stages require ______________ that aid in the translation process
Initiation, elongation, termination
Protein “factors”
The initiation stage of translation brings together…
First, a small ribosomal subunits binds with….
mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
mRNA and a special initiator tRNA
The __________ moves along the mRNA until it reaches the start codon (AUG)
Proteins called _____________ bring in the large subunit so the initiator tRNA occupies the ____ site
Small subunit
Initiation factors
P
During the _________ stage, amino acids are added one by one to the preceding amino acid
Each addition involves proteins called elongation factorsand it occurs in three steps:….
Elongation
Codon recognition, peptide bond formation, and translocation
Termination occurs when a stop codon in the MRNA reaches the ______ site of the ribosome
This site accepts a protein called a release factor, this causes the addition of a water molecule instead of an amino acid
This reaction releases the polypeptide
A
A number of ribosomes can translate a single mRNA simultaneously, forming a…..
Polyribosome
Proteins may also require ______________ modifications before doing their job
Posttranlational
Free ribosomes mostly synthesize proteins that function in the ________
Bound ribosomes make proteins of the…
Ribosomes are identical and can switch from free to bound
Cytosol
Endo membrane system and proteins that are secreted from the cell
Polypeptide synthesis always begins in the _________
Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER (these are marked by a signal peptide)
Cytosol
______________ binds to the signal peptide
This brings the signal peptide and it’s ribosome to the ER
A signal-recognition particle (SRP)
Prokaryotic cells lack a nuclear envelope, allowing….
In a eukaryotic cell the nuclear envelope separates transcription from translation
-extensive RNA processing occurs in the nucleus
Translation to begin while transcription progresses
What are RNAs diverse functions?
Structural, informational, and catalytic functions
What are properties that enable RNA to perform many different functions?
- can hydrogen bond to other nucleic acid’s
- can assume a three dimensional shape
- has functional groups that allow it to act as a catalyst (ribozyme)
The enzyme __________ directs transcription
Polymerase
________________ are chemical changes in just one base pair of a gene
They change of a single nucleotide and I do you need template strand leads to production of an abnormal protein
Point mutations
In point mutations,
When it codes for a different amino acid….
Stops, no further amino acid coded for, this leads to a non functional protein…
Which is more common?
Missense
Nonsense
Missense
Point mutations within a gene can be divided into what two general categories?
- base-pair substitutes
- base-pair insertions or deletions
Base pair substitution can cause…
Missense or nonsense
Insertion or deletion of nucleotides may alter the reading frame, producing a….
Frameshift mutation
Which type of mutations have a more disastrous effect on the resulting protein? Insertions and deletions? Or substitutions?
Insertions and deletions
______________ are physical or chemical agents that can cause mutations
Mutagens
