Chapter 7 Flashcards
Nucleic Acids
Large molecules composed of a chain of smaller nucleotide molecules
Nucleotide
Composed of one phosphate group (PO3), one 5-carbon, ringed sugar, and one of five nitrogenous base molecules
RNA
- Ribose Sugar
- Adenine, Uracil, Cytosine, and Guanine base molecules
- 100-50000 nucleotides in nucleic acid strand
- single stranded; linear
- variety of functions related to protein synthesis
DNA
- Deoxyribose sugar
- Adenine, Thymine, Cytosine, and Guanine base molecules
- Chromosomes have about 45 million nucleotides in nucleic acid strand
- Double stranded helix; bases bonded by weak hydrogen bonds
- Stores genetic information (genes) that direct RNA to perform protein synthesis
Complementary Base Pairs
Certain bases will form weak hydrogen bonds between them; no exchange of electrons; allow two long strands of DNA to stick together; the second strand is complementary to the first
Central Dogma
DNA replication
Protein Synthesis
- DNA –transcription–> mRNA –translation–> protein
DNA Replication
A process that allows two identical copies of DNA for the bacterial chromosome occurring prior to cell division:
- Helicase unwinds and “unzips” the double stranded helix at the origin of replication (begins process)
- Bacteria have one origin of replication; eukaryotic cells have many (several thousand)
- Unwinds and unzips in both directions (5’ to 3’)
- Complementary base pairing of new nucleotides to the original strands (adenine — thymine; cytosine – guanine)
Chromosome
Short, thick strand of DNA and protein; regulate cellular activity by controlling which genes are expressed to produce proteins
DNA Polymerase
- Proof reads the new complementary nucleotide base pairs
- Joins the new complementary base pairs together
- This proceeds until two identical strands are made; strands will eventually separate
- 500-1000 base pairs in a second
- E. coli has 4,639,221 base pairs
Lead Strand
DNA replication occurs towards the replication fork; nucleotides are added continuously in the 3’ direction
Lagging Strand
DNA replication occurs away from the replicating fork; nucleotides are added in segments in the 5’ direction (Okazaki fragments)
Semiconservative Replication
Type of DNA replication in which half of the original strand of the DNA molecule is conserved in each new DNA molecule produced
Organization of the Chromosome
Circular; made of DNA and protein; divided into genes, each of which is a sequence of DNA nucleotides; Bacterial cells will:
- code for the production of a single protein (coding region
- regulate the expression of genes (regulatory region)
Promotor
An area where RNA polymerase will bind to a chromosome (always unzipped)
Operator
A gene can be turned off by placing a protein here
Triplets
How genes are divided; composed of a sequence of three nucleotides found within the same gene; if the gene codes for a protein, this will code for one specific amino acid found within the protein that will be produced; 64 possible combinations but only 20 different amino acids (more than one for each amino acid)
Stop Triplets
Found at the end of the coding region, they stop the reading of a gene
Protein Synthesis
The joining of amino acids to produce proteins; occurs in two distinct phases: transcription and translation
Transcription
Steps used to convert a segment of DNA (template) into mRNA
mRNA (messenger)
A sequence of codons that is a complementary copy of a single gene; carries the information from the DNA to the ribosome; must be present for translation to occur
Phases of Transcription
- Initiation: The enzyme RNA polymerase attaches to the promotor region of a gene
- Elongation: The enzyme unzips the DNA molecule and moves along the template of DNA, synthesizing a single stranded mRNA strand one nucleotide at a time
- Termination: The enzyme encounters a “stop signal” and terminates the construction of mRNA
- A typical gene is composed of 1000 nucleotides and it takes about 30 seconds to make a copy
Translation
The synthesis of an amino acid strand (protein) from codons found on mRNA
Ribosome
Made of rRNA and protein; mRNA binds here; must be present for translation to occur
tRNA (transfer)
Brings a specific amino acid to the mRNA and ribosome; must be present for translation to occur:
- three nucleotides (anti-codon) which is complementary to the codon found on the mRNA
- charged when a specific amino acid is attached to it
- uncharged, it will not have specific amino acid attached, but will eventually find and attach to become charged
Phases of Translation
- Initiation: mRNA binds to the 30S portion of the ribosome
- Elongation: A protein is constructed, one amino acid at a time
- Termination: The ribosome reaches a “stop codon” which will terminate production of the protein, and the protein is released
Stop Codons
Found at the end of a mRNA strand that signal the termination of protein synthesis; UAA, UAG, and UGA
Erythromycin
An antibiotic that binds to the 50S subunit, inhibiting protein synthesis
The Elongation Phase of Translation
- P site: first tRNA will bind here, it is complementary to the first mRNA codon
- A site: second tRNA will bind here, it is complementary to the second mRNA codon
- the two charged tRNA will release their amino acid which form peptide bonds between them, forming a short polypeptide
- the mRNA shifts over one codon and the process continues one amino acid at a time, until a stop codon is reached
Environmental Effects on Anabolic Chemical Reactions
Bacteria live in environments that are changing rapidly; their energy supply or supply of essential nutrients may “dry up”; they must be able to control their biochemical pathways in order to conserve energy (90% of energy used goes to protein synthesis) and spare materials
How Bacteria Conserve Energy and Spare Materials
- Will utilize any and all molecules found within the environment instead of producing them themselves; genes that control the production of certain molecules will be turned off during periods of plenty: energy is conserved and can be used in cell division
- When molecules dry up, the macromolecule must be produced by the machinery of the cell; genes must be able to turn on when needed: energy reserves are used up inside the cell and cell division occurs slowly
End Product Repression
The end product of a series of chemical reactions will inhibit the expression of a gene and prevent further synthesis of all those enzymes necessary to produce the end product (turns genes on or off); e.g., production of the five enzymes responsible for the production of tryptophan
Production of Tyrptophan
- Five genes (one of each enzyme) are located side by side and controlled by the same promotor and operator region (operons); if RNA polymerase attaches to the promotor and no inhibitor exists, then all five genes will be expressed
- Another gene is responsible for the production of an inactive inhibitor protein; it will not bind to the operator region unless this end product is very abundant
- If so, then it will bind to the inhibitor protein, changing its shape, and allowing it to bind to the operator region; the synthesis of all the enzymes are inhibited; once the enzymes within the cell are used up, synthesis of this product will cease
Feedback Inhibition
The end product will inhibit the function of one enzyme (of a series of enzymes) responsible for the synthesis of the end product
Non-Competitive Inhibition
An inhibitor molecule binds to the allosteric site of an enzyme and permanently changes the shape of the enzyme, preventing the substrate from binding to the enzyme
Competitive Inhibition
An inhibitor molecule binds to the active site of an enzyme and prevents the substrate from binding to the enzyme
