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43 Cards in this Set
- Front
- Back
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The production of _________ provides the link between phenotype and genotype |
proteins |
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List the three discoveries that led to the fundamental relationship between genes and proteins |
Garrod Beadle and Tatum Srb and Horowitz
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Describe Beadle and Tatum's discovery, conclusion and the hypothesis it led to |
-bread mould. Neurospora Crassa -Neurospora has modest food requirements, categorized as a "minimal medium" -Wild Type in minimal medium: could use their metabolic pathways to produce all other molecules they needed -Mutant type in minimal medium: could not survive -placed in "complete growth medium" that could support mutant -the supplement that allowed growth indicated the metabolic defect ex: if supplemented with amino acid arginine - could conclude that mutant could not synthesize arginine
Conclusion: each gene dictates production of a specific enzyme Hypothesis: "One-gene one-enzyme hypothesis"
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Describe Garrod discovery and the hypothesis it led to |
hereditary condition called Alkaptonuria -urine is black -ppl missing the enzyme needed to metabolize alkapton
Suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions in the cell diseases = "inborn errors of metabolism" |
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Describe Srb and Horowitz discovery and hypothesis |
-arginine mutants fell into three classes - each with defective in a different gene -Experiment tested two two hypotheses: 1) Beadle and Tantum "one gene one enzyme" 2) arginine-sythesizing pathway (metabolic pathway of arginine involved a precursor nutrient and intermediate molecules)
Conclusion: each class of mutant was unable to carry out one step b/c it lacked a necessary enzyme that was needed to convert intermediate molecules into the next
Conclusion: each mutated gene must dictate the production of one enzyme Hypothesis: supported the "one gene, one-enzyme" |
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The one-gene one polypeptide hypothesis |
- all genes produce proteins, but some proteins are not enzymes -therefore hypoth revised to "one gene-one protein" hypothesis -and many proteins are made up of several polypeptides (each of which has its own gene EX: hemoglobin) -therefore: "one gene, one polypeptide" |
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transcription is, it produces |
-the synthesis of RNA from info of DNA -mRNA |
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translation is, it produces |
synthesis of polypeptide using mRNA |
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The site of translation is |
Ribosomes -facilitates the orderly linking of amino acids into polypeptide chains |
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how do prokaryotes and eukaryotic cells differ in process of Translation. Why? |
in Prokaryotes, translation can begin before transcription has finished
b/c in Eukaryotic cells, the nuclear envelope divides separates transcrip from translat -mRNA requires modifications before leaving the nucleus |
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Why does getting from DNA to protein require two major stages? |
-DNA monomers are nucleotides -protein has monomers that are amino acids -nucleic acids and proteins contain info written in two different chemical languages -nucleotide sequence of mRNA must be translated into into amino acid sequence of polypeptide (at Ribosome) |
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How does DNA and RNA differ (3) |
-RNA contains ribose instead of deoxyribose as its sugar -RNA has nitrogenous base uracil instead of thymine -RNA single strand -carries genetic message of DNA to protein synthesizing machinery of cell |
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Central Dogma |
DNA --> RNA --> Protein
Transcription --> translation |
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How many amino acids? How many nucleotides? |
20 amino acids 4 nucleotides |
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name for triplet code |
codons |
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codons |
complementary non-overlapping three-nucleotide words of mRNA -translated into chain of amino acids -forms polypeptide |
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are all genes transcribed from the same side of DNA strand? |
no, same gene always on same side, but diff genes can come from diff sides of same DNA double strand |
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how many codons? how many stop codons? |
64 codons 3 of which are STOP signals to end translation |
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what is it meant by saying that the genetic code is redundant but there is no ambiguity |
more than one codon can specify a particular amino acid -but one codon can ONLY specify one amino acid |
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T/F : genetic code is universal example |
true - even shared by simplest bacteria and most complex animals ex: CCG is translated into amino acid proline in all organisms example: florescent protein in jellyfish gene is injected into pig eggs - produces fluorescent pig nose, or luminescent tobacco plant with luminescent firefly gene |
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Reading frame |
extracting the intended message requires reading of symbols in correct grouping |
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What modifications do eukaryotic cells undergo after transcription and before translation? |
Each end is modified: 1) 5' end receives a modified guanine nucleotide 5' cap 2) 3' end receives a poly-A tail 3) Introns - untranslated regions (UTRs) on either end of Exons (protein-coding segment) are spliced |
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What does RNA splicing result in? |
removes introns and joins exons |
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What is the functional importance of introns if they are spliced out? |
1. Regulation: some introns contain sequences that regulate gene expression 2. Alternative RNA splicing: some genes can express more than one polypeptide depending on what segment is treated as exon 3. Exon shuffling: increases probability of crossing over between the exons of alleles of a gene - more terrain for crossover without interrupting sequencing |
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T/F the number of different proteins an organism can produce is greater than the number of genes |
True: because of Alternative RNA splicing -some segments are treated as exons, other times treated as introns |
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Domains of proteins |
Proteins often have an architecture made up of modules. Consists of domains: discrete structural and functional regions |
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Exon shuffling and potential result |
increases probability of crossing over between the exons of alleles of a gene - more terrain for crossover without interrupting sequencing -might result in evolution of new proteins with altered structure and function |
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Mutations: 1) define 2) when can they occur? |
1) changes in the genetic material of a cell or virus 2) spontaneous mutations can occur a)during DNA replication b) recombination c) repair
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Mutagens |
physical or chemical agents that can cause mutations ex: x-rays, UV light |
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point mutations |
changes in a single nucleotide pair of a gene -leads to the production of an abnormal protein ex: sickle cell disease, or familial cardiomyopathy |
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2 types of small scale mutations |
1) single nucleotide pair substitutions 2) nucleotide-pair insertions or deletions |
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single nucleotide pair substitutions: 1) define 2) 3 types |
1) the replacement of one nucleotide and its partner with another pair of nucleotides 2) Silent mutation: Missense mutations: Nonsense mutations |
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Silent mutation, define and effects |
Change to pair but same amino due to redundancy: Effect: no observable effect on phenotype |
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Missense mutation, define and effects |
still codes for an amino acid BUT a change of one amino acid to another Effect: little effect on protein. New amino may have properties similar to the amino acid it replaced - or it could be a region of protein that the sequence wasn't essential to function |
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Nonsense mutation, define and effect |
point mutation that changes codon for an amino acid into a stop codon Effect: results in translation to be terminated prematurely and resulting polypeptide will be shorter = almost always NON FUNCTIONAL PROTEIN |
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Insertions and deletions |
additions or losses of nucleotide pairs in a gene |
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Effects of insertions and deletions |
frame shift mutations |
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Frameshift Mutation |
alters the reading frame of genetic message -occurs whenever the number of nucleotides inserted or deleted is not a multiple of three -all nucleotides that are downstream of deletion or insertion will be improperly grouped into codons |
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reading frame |
the triplet grouping of nucleotides on the mRNA that is read during translation |
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Cystic Fibrosis: Where is the mutation, What does that protein regulate |
1) CFTR allele 2)the movement of salt in and out of cells, via channels found in epithelial cells -transports chloride ions out of cell -profound impact on fluid balance |
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Why is CFTR a pleotropic trait? |
many different organs are effected by its expression, and therefore area also effected by its mutation |
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What makes treatment of CFTR mutations so complicated? |
-over 2000 entries of mutations -drugs need to be designed for specific mutation ex 1: Ataluren -allows full read through of premature nonsense stop signals in mRNA. Therefore, allows full-length protein production ex 2: Kalydeco -a 'potentiator' that helps the ion channels remain open |
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Four different descriptions of "a gene" |
1. unit of inheritance 2. region of nucleotide sequence in a chromosome 3. DNA sequence that codes for a polypeptide chain 4. DNA sequence that expressed to produce a final functional product (either RNA or polypeptide) |
