(T/F) Multiple genes code for one polypeptide
False; this has been refuted by the discovery of the one-gene, one polypeptide relationship
In protein-synthesis, the function of a gene is what?
1) The function of a gene is to inform the production of a single, specific polypeptide.
During _________, the info in a DNA sequence (a gene) is copied into a complementary RNA sequence
During __________, this RNA sequence is used to create the amino acid sequence of a polypeptide
What is the central dogma of molecular biology?
1) DNA --(transcription)->RNA
What are the 3 differences between DNA and RNA
1) RNA generally consists of only one polypeptide strand
2) The sugar molecule found in RNA is ribose, rather than the deoxyribose found in DNA
3) The fourth base in RNA is uracil (U), which is similar to thymine but lacks the methyl (-CH₃) group
Three types of RNA participate in protein synthesis...what are they?
1) Messenger RNA (mRNA)
2) Transfer RNA (tRNA)
3) Ribosomal RNA (rRNA)
_________ _____ carries a copy of a gene sequence in DNA to the site of protein synthesis at the ribosome
1) Messenger RNA (mRNA)
________ ___ carries amino acids to the ribosome for assembly into polypeptides
1) Transfer RNA (tRNA)
________ ___ catalyzes peptide bond formation and provides a structural framework for the ribosome
1) Ribosomal RNA (rRNA)
3 nucleotides in messenger RNA that direct the placement of a particular amino acid into a polypeptide chain are often called _________ (the three letter words)
An _________ is the three nucleotides in transfer RNA that pair with a complementary triplet (a codon) in messenger RNA
Synthesis of DNA from RNA is called ________ _________, and not surprisingly such viruses are called ______________
1) Reverse Transcription
Where does transcription take place in eukaryotes? WHat about translation?
1) Inside the nucleus
2) Inside the cell (outside of the nucleus)
How do RNA viruses break the typical central dogma?
1) Viruses generally have RNA rather than DNA as genetic material. RNA can act as an info carrier but since its single stranded they have to transcribe RNA into RNA, making an RNA strand that is complementary to their genomes. (pg. 295)
______ ___________ from both prokaryotes and eukaryotes catalyze the synthesis of RNA from the DNA template.
1) RNA polymerases
In _________ RNA polymerase binds to the promoter and starts to unwind the DNA strands
In __________ RNA polymerase moves along the DNA template strand from 3' to 5' and produces the RNA transcript by adding nucleotides to the 3' end of the growing RNA
In ________ RNA polymerase reaches the termination site, the RNA transcript is set free from the template.
Three of the codons (______, ______, _______) are stop codons, or termination signals for translation.
The _________ ______ relates genes (DNA) to mRNA and mRNA to the amino acids that make up proteins
1) Genetic Code
What happens when a code is ambiguous?
1) If the code were ambiguous, a single codon could specify either of two (or more) different amino acids, and there would be doubt about which amino acid should be incorporated into the polypeptide chain.
What happens when a genetic code is redundant?
1) A given amino acid may be encoded by more than one codon, but a codon can code for only one amino acid.
(T/F) DNA code in snakes would code for the same amino acids in humans
1) True; the genetic code is nearly universal
Eukaryotic genes may also contain noncoding base sequences , called _______ (intervening regions)
One or more introns may be interspersed with the coding sequences, which are called ________(expressed regions)
During the transcription of a eukaryotic gene what 3 things happens?
1) The exons and introns of the of the coding region are transcribed
2) The introns are removed
3) The spliced exons are ready for translation after processing
How can you locate introns within a eukaryotic gene?
1) Nucleic Acid Hybridization; the method that originally revealed the existence of introns
Nucleic Acid Hybridization has two steps...what are they?
1) The target DNA is denatured by heat to break the hydrogen bonds between the base pairs and separate the two strands
2) A single-stranded nucleic acid from another source (called a probe) is incubated with the denatured DNA. If the probe has a base sequence complementary to the target DNA, a probe-target double helix forms by hydrogen bonding between the bases. B/c the two strands are form different sources, the resulting double-stranded molecule is called a hybrid.
At the end of the gene, downstream from the coding region, is a DNA sequence appropriately called the ________, which signals the end of transcription
In some cases, the separated exons encode different functional regions, or ________, of the protein
Two steps in the processing of pre-mRNA take place in the nucleus, one at each end of the molecule...what are they?
1) A G Cap (a chemically modified molecule of GTP) is added to the 5' end of the pre-mRNA as it is transcribed. It facilitates the binding of mRNA to the ribosome for translation
2) Poly A tail is added to the 3' end
A process called _____ __________ removes the introns and splices the exons together
1) RNA splicing
As soon as the pre-RNA is transcribed, several __________ ________ _____________ ___________ bind at each end
1) Small nuclear Ribonucleoprotein particles (snRNP's)
At the boundaries between introns and exons are _________ ________-short stretches of DNA that appear with little variation, in many different genes
1) Consensus sequences
Using energy from ATP, proteins are added to form a large RNA-protein complex called a __________. This complex cuts the pre-mRNA, releases the introns, and joins the ends of exons together to produce mature mRNA
The translation of mRNA into proteins requires a molecule that links the info contained in mRNA codons w/ specific amino acids in proteins. That function is performed by ___________
1) transfer RNA (tRNA)
Two key events that must take place to ensure that the protein made is one specified by the mRNA : what are they?
1) The tRNA's must read MRNA codon's correctly
2) The tRNA's must deliver the amino acids that correspond to each mRNA codon
The tRNA molecule has three functions...what are they?
1) It binds to a particular amino acid. When it is carrying an amino acid, the tRNA is said to be "charged"
2) It associates with mRNA
3) It interacts with ribosomes
What are the three sites of tRNA binding and what happens at each?
1) The A (amino acid) site
2) The P Polypeptide site
3) The E (exit site)
The _____________ site is where the charged tRNA anticodon binds to the mRNA codon, thus lining up the correct amino acid to be added to the growing polypeptide chain
1) The A (amino acid) site
The ___________ site is where the tRNA adds its amino acid to the polypeptide chain
1) The P (polypeptide) site
The _________ site is where the tRNA, having given up its amino acid, resides before being released from the ribosome and going back to the cytosol to pick up another amino acid and begin the process again
1) The E (exit) site
The translation of mRNA begins with the formation of an _________ _________, which consists of a charged tRNA and a small ribosomal unit, both bound to the mRNA
1) Initiation Complex
A __________ consists of multiple ribosomes and their growing polypeptide chains moving along an mRNA molecule
A ______ _______ ________, allows hydrolysis of the bond between the polypeptide chain and the tRNA in the P site
1) Protein Release Factor
A ________ ________-is an "address label" indicating where in the cell the polypeptide belongs.
1) Signal Sequence
Protein synthesis always begins on free ribosomes in the cytoplasm. But as a polypeptide chain is made, the info contained in its amino acid sequence gives it one of two sets of further instructions...what are they?
1) "Complete translation and be released to an organelle, or remain in the cytosol"
2) "Stop translation, go to the endoplasmic reticulum, and finish synthesis there"
A signal sequence binds to a specific receptor protein, appropriately called a ________ ________, on the outer membrane of the appropriate organelle.
1) Docking Protein
After removal of the terminal signal sequence in the lumen of the ER, additional signals are needed to direct the protein to its destination. These signals are of two kinds; what are they?
1) Some are sequences of amino acids that allow the protein's retention within the ER
2) Others are sugars, which are added in the Golgi Apparatus. The resulting glycoproteins end up either at the plasma membrane or in a lysosome (or plant vacuole), or are secreted, depending on which sugars are added