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Ch 3 - Cells
Terms in this set (12)
1. RNA polymerase binds to the promoter region of a gene and separates the two strands of the DNA double helix in the region of the gene to be transcribed.
2. Free ribonucleotide triphosphates base-pair with the deoxynucleotides in the template strand of DNA.
3. The ribonucleotides paired with this strand of DNA are linked by RNA polymerase to form a primary RNA transcript containinga sequence of bases complementary to the template strand of the DNA base sequence.
4. RNA splicing removes the intron-derived regions, which contain noncoding sequences, in the primary RNA transcript and splices together the exon-derived regions, which encode specific amino acids, producing a molecule of mature mRNA.
1. The mRNA passes from the nucleus to the cytoplasm, where one end of the mRNA binds to the small subunit of a ribosome.
2. Free amino acids are linked to their corresponding tRNAs by aminoacyl-tRNA synthetase.
3. The three-base anticodon in an amino acid-tRNA complex pairs with its corresponding codon in the region of the mRNA bound to the ribosome.
4. The amino acid on the tRNA is linked by a peptide bond to the end of the growing polypeptide chain.
5. The tRNA that has been freed of its amino acid is released from the ribosome.
6. The ribosome moves one codon step along mRNA.
7. The previous four steps are repeated until a termination sequence is reached, and the completed protein is released from the ribosome.
8. In some cases, the protein undergoes posttranslational processing in which various chemical groups are attached to specific side chains and/or the protein is split into several smaller peptide chains.
when a protein contains two binding sites, the noncovalent binding of a ligand to one site can alter the shape of the second binding site and, therefore, the binding characteristics of that site
two ways to alter proteins
1. allosteric modulation
2. covalent modulation
alteration of a protein's shape, and therefore its function, by the covalent binding of various chemical groups to it
At chemical equilibrium, product concentrations are only slightly higher than reactant concentrations.
At chemical equilibrium, almost all reactant molecules have been converted to product.
5 Characteristics of Enzymes
1. An enzyme undergoes no net chemical change as a consequence of the reaction it catalyzes.
2. The binding of substrate to an enzyme's active site has all the characteristics—chemical specificity, affinity, competition, and saturation—of a ligand binding to a protein.
3. An enzyme increases the rate of a chemical reaction but does not cause a reaction to occur that would not occur in its absence.
4. Some enzymes increase both the forward and reverse rates of a chemical reaction and thus do not change the chemical equilibrium finally reached. They only increase the rate at which equilibrium is achieved.
5. An enzyme lowers the activation energy of a reaction but does not alter the net amount of energy that is added to or released by the reactants in the course of the reaction.
A change in enzyme activity occurs when either allosteric or covalent modulation alters the properties (for example, the structure) of the enzyme's active site.
Glycolysis (from the Greek glycos, "sugar," and lysis, "break- down") is a pathway that partially catabolizes carbohydrates, pri- marily glucose. It consists of 10 enzymatic reactions that convert a six-carbon molecule of glucose into two three-carbon molecules of pyruvate, the ionized form of pyruvic acid .the reactions produce a net gain of two molecules of ATP and four atoms of hydrogen, two transferred to NAD+ and two released as hydrogen ions:
the second of the three pathways involved in nutrient catabolism and ATP produc- tion. It utilizes molecular fragments formed during carbohydrate, protein, and fat breakdown; it produces carbon dioxide, hydrogen atoms (half of which are bound to coenzymes), and small amounts of ATP.
mechanism by which energy derived from nutrient molecules can be transferred to ATP. The basic principle behind this pathway is simple: The energy transferred to ATP is derived from the energy released when hydrogen ions combine with molecular oxygen to form water. The hydrogen comes from the NADH + H+ and FADH2 coenzymes generated by the Krebs cycle, by the metab- olism of fatty acids (see the discussion that follows), and—to a much lesser extent—during glycolysis.
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