Bio 110 Chapter 12

Archbold Garrod

1908, _____________________ first proposed relationship between genes and the production of enzymes
-studied patients with metabolic defects, or "inborn errors of metabolism"

alkaptonuria

-patient's body accumulates abnormal levels of homogentisic acid (alkapton)
-recessive pattern of inheritance
—hypothesis: "Disease is due to missing enzyme"

Archbold Garrod

1908, _____________________ first proposed relationship between genes and the production of enzymes
-studied patients with metabolic defects, or "inborn errors of metabolism"

alkaptonuria

-patient's body accumulates abnormal levels of homogentisic acid (alkapton)
-recessive pattern of inheritance
—hypothesis: "Disease is due to missing enzyme"

beadle and tatum

-worked on Neurospora crassa (common bread mold)
-wild type
-mutant strains
-each single mutation resulted in the requirement for a single type of vitamin
-hypothesis: "One gene, one enzyme"
-1940s

wildtype

can grow on minimal medium [carbon source (sugar), inorganic salts, and biotin]

mutant strains

unable to grow unless supplemented with specific substances (vitamins or amino acids)

arginine

beadle and tatum's study showed multiple mutants required _____________ to grow

one gene-one polypeptide

because many proteins are composed of several polypeptides, each of which has its own gene (hemoglobin), Beadle and Tatum's hypothesis is now restated as the ____________________________ hypothesis

gene expression

the process by which DNA directs protein synthesis

transcription

_________________ is the synthesis of R N A using information in D N A
-from nucleic acid (DNA) to nucleic acid (RNA)
-produces messenger RNA (mRNA)
-mRNA specifies the amino acid sequence of a polypeptide

Translation

__________________ is the synthesis of a polypeptide, using information in the mRNA
-from nucleic acid (RNA) to amino acids (polypeptide)
-ribosomes are the sites of translation

RNA processing

eukaryotes also have an intervening step called ___________________ where pre-mRNA is processed into active mRNA

polypeptides

some genes do not encode _________________
-an RNA is the final functional product
-structural RNAs
-regulatory RNAs

transcription

mRNA produced by _________________ is immediately translated without additional processing

RNA processing

eukaryotic RNA transcripts are modified through ____________________ to yield the finished mRNA

bacteria

in _________________, translation of mRNA can begin before transcription has finished

gene

an organized unit of base sequences that enables a segment of DNA to be transcribed into RNA and ultimately results in the formation of a functional product

transfer RNA (tRNA)

translates mRNA into amino acids

ribosomal RNA (rRNA)

part of ribosomes

RNA polymerase

(enzyme)
-pries the DNA strands apart and joins together the complementary RNA nucleotides
-assembles RNA transcripts in the 5'→ 3' direction
-unlike DNA polymerases, RNA polymerases can start a chain without a primer

promoter

where RNA polymerase attaches
-signals the beginning of transcription

terminator

signals the end of transcription

regulatory sequence

site for the binding of regulatory proteins. the role of regulatory proteins is to influence the rate of transcription

5' to 3'; 3' to 5'

in all cases, synthesis of RNA transcript is read ____________ and DNA template strand reads ___________

initiation, elongation, and termination

the three stages of transcription are...

initiation

stage 1 of transcription
-recognition step
—in bacteria, sigma factor causes RNA polymerase to recognize promoter region
—stage completed when DNA strands separatenear promoter to form open complex

elongation

stage 2 of elongation
-RNA polymerase synthesizes RNA
—template DNA strand used for RNA synthesis
—opposite DNA strand is not used

RNA sequence

-complementary to template DNA
-antiparallel to template DNA
-uracil substituted for thymine

termination

stage 3 of transcription
-RNA polymerase reaches termination sequence
-causes both the polymerase and newly-made RNA transcript to dissociate from DNA

polymerase

in bacteria, the _____________________ stops transcription at the end of the terminator
t-he mRNA can be translated without further modification

RNA polymerase II

________________ requires 5 general transcription factors to initiate transcription

RNA polymerase II

transcribes mRNA

RNA polymerase I and III

transcribes nonstructural genes for rRNA and tRNA

eukaryotic

____________________ cells do not use sigma factors in transcription

mature mRNA

in eukaryotic cells, mRNAs are made in a longer pre-mRNA form that requires processing into _____________________

nuclear enzymes

modify pre-m R N A before the genetic messages are transported to the cytoplasm

guanosine (G) 5'cap

the 5' end receives a modified _____________________

poly-A tail

The 3' end gets a _______________ (many As added)

exons

regions that are usually translated into amino acid sequences (and found in the mature mRNA)

introns

regions that are not translated (not in the protein)

RNA splicing

In __________________, the introns are removed and the exons are joined together

spliceosomes

RNA splicing is carried out by ____________________
-consist of proteins and small nuclear RNA's

ribozymes

_______________________ are RNA molecules that function as enzymes

alternative RNA splicing

splicing can occur more than one way to produce different products
-many genes can give rise to two or more different polypeptides, depending on which segments are used as exons

triplet code

information flow from gene to protein is based on a _______________: a series of non-overlapping, three-nucleotide bases

genetic code

sequence of bases in an mRNA molecule

codons

groups of three nucleotide bases are ___________
-most specify a particular amino acid

64

there are _____ codons

61

_____ codons code for amino acids

3

____ codons are "stop" signals to end translation

degenerate

more than one codon can specify the same amino acid

ambiguous

codons are not ___________________: no codon specifies more than one amino acid

genetic code

the __________________ is nearly universal
-shared by the simplest bacteria and the most complex plants and animals
-genes from one species can be transcribed and translated after being transplanted to another

5' to 3'

during translation, the mRNA codons are read in the _______________ direction
-codons must be read in the correct reading frame (correct order) to produce the specified polypeptide
-codons are read one at a time in a nonoverlapping fashion

L-shaped

tRNAs are roughly _______________

anticodon

one end of the L contains the ________________ that base-pairs with an mRNA codon

anticodon

a nucleotide triplet that can base-pair with the complementary codon on mRNA

aminoacyl-t RNA synthetase

first, a correct match between a tRNA and an amino acid, done by the enzyme ______________________________

wobble

flexible pairing at the third base of a codon allows some tRNAs to bind to more than one codon

transfer RNA (tRNA)

a cell translates an mRNA message into protein with the help of ____________________

tRNA

_______________ transfer amino acids to the growing polypeptide in a ribosome

ribosomes

_________________ facilitate specific coupling of tRNA anticodons with mRNA codons during protein synthesis

cytosolic ribosomes

composed of small and large subunits
-the large and small subunits join to form a ribosome only when attached to an mRNA molecule

ribosomal RNAs (rRNAs)

The large and small ribosomal subunits are made of proteins and _________________________

P site

peptidyl site

E site

exit site

initiation, elongation, and termination

the three stages of translation for RNA are...

initiation

mRNA, first tRNA and ribosomal subunits assemble

elongation

synthesis from start codon to stop codon

termination

complex disassembles at stop codon releasing the completed polypeptide

GTP

the energy for the three stages of translation is provided by hydrolysis of _______

reading frame

the start codon in initiation is important because it establishes the _____________________ for the mRNA

guanosine cap

instead of a ribosomal-binding sequence, mRNAs have ____________________ at 5' end
-recognized by cap-binding proteins

step 1 of elongation

-aminoacyl tRNA brings a new amino acid to the A site
-binding occurs due to codon / anticodon recognition
—elongation factors hydrolzye GTP to provide energy to bind tRNA to A site
—peptidyl tRNA is in the P site
-aminoacyl tRNA is in the A site

step 2 of elongation

-peptide bond is formed between the amino acid at the A site and the growing polypeptide chain
-the polypeptide is removed from the tRNA in the P site and transferred to the amino acid at the A site
—called the peptidyl transfer reaction
—rRNA catalyzes peptide bond formation (the ribosome is a ribozyme)

peptidyl transfer reaction

the polypeptide is removed from the tRNA in the P site and transferred to the amino acid at the A site

step 3 of elongation

-movement or translocation of the ribosome toward the 3' end of the mRNA by one codon
—shifts tRNAs at the P and A sites to the E and P sites
—the next codon is now at the A spot
—uncharged tRNA exits from E spot

termination

-when a stop codon is found in the A site, translation ends
—3 stop codons - UAA, UAG, UGA
—recognized by release factors
-completed polypeptide is attached to a tRNA in the P site and stop codon in the A site
—release factor binds to stop codon at the A site
—bond between polypeptide and tRNA hydrolyzed to release polypeptide
—ribosomal subunits and release factors disassociate

bacteria and eukaryotes

in ________________________________________, multiple ribosomes translate an m R N A at the same time
-once a ribosome is far enough past the start codon, another ribosome can attach to the m R N A

polyribosomes

strings of ribosomes called _______________________ (or polysomes) can be seen with an electron microscope

bacteria

in ________________, the transcription and translation can take place simultaneously

bacterial ribosomes

structural differences between prokaryotes and eukaryotes are exploited by antibiotics to inhibit _______________________ only
-antibiotics that inhibit bacterial translation can treat bacterial infections