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Ch. 17 study guide
Palmtag
| Question | Answer |
|---|---|
| What is a protein? | a biologically functional molecule consisting of one or more polypeptides. |
| What are some of the functions of proteins? | structural support, storage, transport, cellular communication, movement, and defense against foregin substances. |
| What is the name of the units that compose a protein? | Amino acids. |
| What is the general formula of an amino acid? | amino, carboxyl, hydrogen, R |
| How many different amino acids are commonly present in proteins? | 20 amino acids. |
| What is the difference between different amino acids? | The amino acid's R group. |
| What is the name of the bond that is formed between two amino acids by a dehydration reaction? | A peptide bond. |
| How many levels of structure are present in a protein? | 4: Primary, secondary, tertiary, quaternary. |
| What types of chemical bonds are responsible for the primary, secondary, tertiary and quaternary structure of proteins? | primary: covalent secondary: hydrogen tertiary: hydrogen & ionic quaternary: hydrogen |
| How many polypeptide chains are there in a protein? | 4-> 2 beta and 2 alpha |
| What did Garrod hypothesize, but was unable to provide proof through scientific experimentation? | That a gene dictates the production of a specific enzyme. |
| How were Beatle and Tatum able to support Garrod’s hypothesis through scientific research? What does “one gene –one protein” mean? | each mutant was defective in a single gene-> the results provided strong support for the one-gene-one enzyme hypothesis, which states that the function of a gene is to dictate the production of a specific gene. |
| What is transcription, where does it take place, why is it necessary? | -The synthesis of RNA using information from the DNA. -In the nucleus -To serve as a template for assembling a complementary sequence of RNA nucleotides. |
| What enzyme transcribes mRNA? | RNA polymerase. |
| What is the difference between the template and non-template strand of DNA? | -The template strand is the DNA strand that provides the pattern/template for ordering the sequence of nucleotides -The non-template strand contains coding genes |
| Describe the direction of a template strand of DNA relative to a mRNA transcript. | -Template strand 3'-5' -mRNA transcript 5'-3' |
| -What is translation, where does it occur? | -The synthesis of a polypeptide using the info. in the mRNA -In the cytoplasm free: throughout cytoplasm fixed: along ribosomes |
| Compare and contrast transcription in prokaryotes? | prok: mRNA is produced by transcription & is immediately translated w/o additional processing.Both: use prolymerases & promoters activate synthesis |
| Compare and Contrast transcription in eukaryotes? | euk:the nucleus provides a separate compartment for transcription. The original RNA transcript: pre-RNA is processes in various ways before leaving the nucleus as mRNA.Both: use prolymerases & promoters activate synthesis. |
| What is the “central dogma of molecular biology”? | DNA->RNA->protein |
| How can four nucleotides code for twenty amino acids? | They work in 3's. 4^3=64 which is>20. |
| Be able to transcribe a mRNA transcript from a DNA template strand. | DNA template A C C A A A C C G A U G G U U U G G C U transcribing mRNA |
| What are codons? | The mRNA base triplets |
| How does a segment of mRNA code for an amino acid and the sequence of amino acids in a protein? | during translation, the sequence of codons along a mRNA molecule is decoded into a sequence of amino acids making a polypeptide chain. |
| What are start and stop codons? | start: AUG(met) where translation starts stop: UGA, UAA, UAG, where translation stops |
| Why is the genetic code redundant but not ambiguous? | multiple codons may code for the same amino acid, however, no codon codes for more than one amino acid ex: although codons GAA and GAG both code specify glutamic acid (redundancy), neither of them ever specifies any other amino acid (no ambuigity). |
| Describe how Nirenburg was able to show that the sequence of nucleotides in mRNA determined the sequence of amino acids in a protein. | It could only contain one codon in repetition:UUU-Nirenburg added this "poly-U" to a test tube containing amino acids, ribosomes, etc...it was determined that the mRNA codon UUU specifies the amino acid phenylaline. |
| Describe the reading frame for the genetic code? | on an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis |
| How does a frame shift affect the reading frame? | when a frame is shifted, it changes the meaning of a protein. |
| Be able to translate a mRNA transcript into a protein. | ? |
| Why do we say that the genetic code is universal, are there exceptions? | it's shared by organisms from the simplest bacteria to the most complex plants & animals. |
| promoter? | the DNA sequence where RNA polymerase attaches & initiates transcription |
| TATA box? | a nucleotide sequence containing TATA; a crucial promoter for DNA sequence |
| Transcription factors? | a collection of proteins that mediate the binding of RNA polymerase & the initiation of transcription |
| RNA polymerase? | pries the 2 strands of DNA apart & joins tog. RNA nucleotides complimentary to the DNA template strand, elongating the RNA polynucleotide. |
| binding? | takes place in a precise location & orientation on the promoter. |
| initiation? | after RNA polymerase binds to the promoter, the DNA strands unwind & the polymerase initiates RNA synthesis @ the start point on the template strand. |
| elongation? | the polymerase moves down stream, unwinding the DNA & elongating the RNA transcript 5'-3'. in the wake of transcription the DNA strands re-form a double helix. |
| termination? | the RNA transcript is released & the polymerase detaches from the DNA. |
| How does termination differ in prokaryotes and eukaryotes? | euk: RNA ply II transcribes a sequence on the DNA- polyadenylation signal sequence. then @ pt. 10-35 nucleotides down stream from AAUAAA proteins associated w/ the growing RNA transcript cut it free from the polymerase releasing the pre-mRNA |
| How does termination differ in prokaryotes and eukaryotes? | pro: the transcribed terminator functions as the termination signal causing the polymerase to detach from the DNA & release the transcript |
| What is mRNA processing? | when both ends of the primary transcript are altered |
| 5’cap | when a form of Guanine is added to the 5' end after transcription. |
| UTR's | part of the mRNA that will not be translated into a protein. |
| polydenylation signal sequence | hexanucleotide of mRNA, usually AAUAAA, that identifies the location of 3' pre-mRNA cleavage and polydenylation. |
| poly-A tail | formed @ the 3' end when an enzyme adds 50-250 more adenine nucleotides |
| introns | the noncoding segments of nucleic acid that lie between coding regions. |
| exons | sequences of RNA that exit the nucleus. |
| What is mRNA splicing, What does the splicing, what is spliced, where does it occur, why is this necessary? | process of removing introns.Spliceosome does the splicing, two exons are being spliced together, occurs in the nucleus.necessary for the passage of mRNA from the nucleus to the cytoplasm. |
| What are the advantages of RNA splicing? What is a ribozyme, are they common? | *ribozyme- RNA molecules that function as enzymes -RNA splicing can occur without proteins or even additional RNA molecules: the intron RNA functions as a ribozyme and catalyzes its own incision. |
| Where does translation occur? What types of RNA are involved? Describe the origin of each type of RNA. What is a ribosome, what are its components? | *cytoplasm *transfer RNA (tRNA) |
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