biochem gene expression and protein synthesis Flashcards
is the turning on or activation of a gene
- Gene expression
the process by which information encoded in a DNA molecule is copied into an mRNA molecule.
- Transcription
starts when the DNA double helix begins to unwind near the gene to be transcribed.
- Transcription
How many strand of the DNA is transcribed.
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assemble along the unwound DNA strand in a complementary sequence.
- Ribonucleotides
- catalyze transcription: poly I for rRNA formation, poly II for mRNA formation, and poly III for tRNA formation.
polymerases
- A eukaryotic gene has two parts
structural and regulatory genes
that is transcribed into RNA; the structural gene is made of exons and introns.
structural genes
genes that controls transcription; the regulatory gene is not transcribed but has control elements, one of which is the
regulatory genes
regulatory genes that controls transcription; the regulatory gene is not transcribed but has control elements, one of which is the
promoter
- There is always a sequence of bases on the DNA strand ca led an
initiation signal
Promoters also contain
consensus sequences
- Promoters also contain consensus sequences such as the
TATA box
- A TATA box lies approximately __base pairs upstream (Figure 25.2).
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- A l three RNA polymerases interact with their promoter regions via _____ that are binding proteins.
transcription factors
- After initiation, RNA polymerase zips up the complementary bases in a process ca led
elongation
- Elongation is in the____ direction
5’ - 3’
- At the end of each gene is a
termination sequence.
- Poly II has two different forms
- At its C-terminal domain, it has ___and ___repeats that can be phosphorylated
Ser and Thr
- When poly II starts initiation, it is
- At its C-terminal domain, it has Ser and Thr repeats that can be
phosphorylated
- After termination of the transcription
it is dephosphorylated
- After termination of the transcription, it is dephosphorylated by a
phosphatase.
- In this manner, poly II is constantly recycled between its
initiation and elongation roles.
- The RNA products of transcription are not necessarily functional RNAs. They are made functional by
post- transcription modification
- The 5’ end acquires a
methylated guanine.
- The RNA products of transcription are
not necessarily functional RNAs.
- The 3’ end acquires a polyA tail that may contain from
100 to 200 adenine residues.
- Functional rRNA also undergoes
post-transcription methylation.
- mRNA, rRNA, and tRNA a l participate in
translation
- Protein synthesis takes place on
ribosomes
- A ribosome dissociates into
larger and a smaller body.
- Together the 40S and 60S ribosomes form a unit on which
mRNA is stretched out.
- In higher organisms, the larger body is called a ___ribosome; the smaller body is called a ____ ribosome
60S ribosome
40S ribosome
- Triplets of bases on mRNA are called
codons
- Each tRNA is specific for
only one amino acid.
- Each ce l carries at least
20 specific enzymes
- Each cell carries at least 20 specific enzymes, each specific for
one amino acid.
- Each enzyme recognizes
only one tRNA.
- The enzyme bonds the activated amino acid to the 3’ terminal -OH group of the appropriate tRNA by an
ester bond.
- At the opposite end of the tRNA molecule is a
codon recognition site
- The codon recognition site is a sequence of three bases ca led an
anticodon
- By ____ the genetic code was broken.
1967,
- AUG also serves as an
initiation signal.
- Only __ and___ have one codon each.
Trp and Met
- 3 (UAA, UAG, and UGA) serve as
termination signals
- More than one triplet can code for the same amino acid; ___, __, and ___, for example, are each coded for by six triplets.
Leu, Ser, and Arg
- The code is almost universal: it the same in viruses, prokaryotes, and eukaryotes; the only exceptions are some
codons in mitochondria.
- There are four major stages in protein synthesis:
- Activation
- Initiation
- Elongation
- Termination
is bound to its own particular tRNA by an ester bond between the carboxyl group of the amino acid and the 3’-OH of the tRNA.
activated amino acid
- For the 15 amino acids coded for by 2, 3, or 4 triplets, it is only the___ letter of the codon that varies
third
the process whereby a base sequence of mRNA is used to create a protein.
translation
amino acid activation
- amino acids
- tRNAs
- aminoacyl-tRNA synthetases
- ATP, Mg2+
The aminoacyl-AMP remains bound to the enzyme and binding of the correct amino acid is verified by an editing site on the tRNA synthetase.
amino acid
There are specific binding sites on tRNAs that are recognized by aminoacyl-tRNA synthetases.
tRNA
- Termination codons (____, ___, or ___) of mRNA.
(UAA, UAG, or UGA)
the various methods used by organisms to control which genes
gene regulation
- In eukaryotes, transcription is regulated by three elements:
promoters, enhancers, and response elements.
promoters are defined by an_____ and _____ such as TATA or GC boxes.
initiator and conserved sequences
______find their targeted sites by twisting their protein chains so that a certain amino acid sequence is present at the surface.
Transcription factors
- Different ____ bind to different modules of the promoter.
transcription factors
a low the rate of synthesis of mRNA
- Transcription factors
- One such conformational twist is provided by
metal binding fingers
- Two other prominent transcription factor conformations are the___and the____
helix-turn-helix
leucine zipper
- Transcription factors also possess____ , which reduce the rate of transcription.
suppressors
are activated by their transcription factors in response to an outside stimulus.
response elements
- During translation, Enzymes called ______catalyze this bonding
aminoacyl-tRNA synthase (AARS)
may speed up transcription
enhancers
- The response element of steroids is in front of and about____base pairs upstream from the starting point of transcription.
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- The stop codons must be recognized by
release factors
- The release factor combines with GTP and binds to the ribosomal A site when that site is occupied by the
termination codon.
- The stop codons must be recognized by
- The release factor combines with GTP and binds to the ribosomal A site when that site is occupied by the termination codon.
- Termination control
- In most proteins, the Met at the N-terminal end is removed by Met-aminopeptidase.
- Certain proteins ca led help newly synthesized proteins to fold properly.
- If rescue by chaperones fails, may degrade the misfolded protein.
- Post-translational control
- In most proteins, the Met at the N-terminal end is removed by
Met-aminopeptidase.
a heritable change in the base sequence of DNA.
mjtation
- If rescue by chaperones fails, _____ may degrade the misfolded protein.
proteasomes
- Certain proteins called ______ help newly synthesized proteins to fold properly
chaperones
- If the original codon is CAT, it may be transcribed onto mRNA as
GUC which codes for Val
- It is estimated that, on average, there is one copying error for every
1010 bases
- Base errors can also occur during
transcription in protein synthesis (a nonheritable error).
a chemical that causes a base change in DNA.
mutagen
- Consider the mRNA codons for
Val, which are CAT, CAC, CAG, and CAA.
- Many changes in base sequence caused by radiation and mutagens do not become mutations because
cells have repair mechanisms called
nucleotide excision repair
DNA from two sources that have been combined into one molecule.
recombinant DNA
recombinant DNA, One example of the technique begins with plasmids found in the cells of
Escherichia coli
a small, circular, double-stranded DNA molecule of bacterial origin.
plasmid
- A class of enzymes called _____ cleave DNA at specific locations.
restriction endonucleases
- The human gene is now spliced into the plasmid by the enzyme
DNA ligase
