Exam #2 (7-9) Flashcards
Nucleic Acid Structure
Large molecules (DNA &RNA) composed of a chain of smaller nucleotides:
- one phosphate group (PO3)
- one 5-carbon ringed sugar
- one of five nitrogenous base molecules
RNA
- Ribose sugar
- Adenine, Uracil, Cytosine, and Guanine base molecules
- 100-50000 nucleotides in a 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 a strand
- Double-stranded helix; bases bond by weak hydrogen bonds
- Stores genetic information (genes) that direct RNA to perform protein synthesis
Complementary Base Pairs
Certain bases form weak hydrogen bonds between them (no exchange of electrons); allow the two long strands of DNA to stick together
DNA Replication
A process that allow two identical copies of DNA for the bacterial chromosome; occurs prior to cell division:
- Helicase unwinds and unzips the double stranded helix at the origin of replication (both directions)
- DNA polymerase proofreads and joins new complementary base pairs together
- This proceeds until two identical strands are made (500-1000 base pairs in a second)
- Two identical strands will eventually separate
Origin of Replication
Distinct region of a DNA molecule at which replication is initiated: one in bacteria, several thousand in eukaryotic cells
Chromosome
Short, thick strand of DNA and protein; circular; divided into genes each of which is a sequence of DNA nucleotides; regulate cellular activity by controlling which genes are expressed to produce proteins
Coding Region
Bacterial genes that code for the production of a single protein
Regulatory Region
Bacterial genes that regulate the expression of genes
Promotor
An area where RNA polymerase will bind (always unzipped)
Operator
A gene can be turned off by placing a protein here
Triplets
Division of genes composed of a sequence of three nucleotides found within the same gene; if the gene codes for a protein, then this will code for one specific amino acid found within the protein that will be produced; 64 possible combinations
Stop Triplets
Found at the end of a coding region; stops the reading of a gene
Stop Codon
Codon that does not code for an amino acid and is not recognized by tRNA; signals the end of the polypeptide chain; UAA, UAG, and UGA
Start Condon
Codon at which translation is initiated; in prokaryotes, typically the first AUG after a ribosome binding site
Lagging Strand
DNA replication occurs away from the replicating fork; nucleotides are added in segments in the 5’ direction (Okazaki fragments)
Lead Strand
DNA replication occurs towards the replication fork; nucleotides are added continuously in the 3’ direction
Transcription
The conversion of one gene found on DNA into mRNA:
- 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
Translation
The synthesis of an amino acid strand from codons found on mRNA:
- Initiation: mRNA binds to the 30S portion of the ribosome
- Elongation: Charged tRNA molecules bind to the 50S portion of the ribosome at two spots simultaneously (P and A sites); charged tRNA molecules release their amino acid which form peptide bonds between them, forming a short polypeptide; mRNA shifts over one codon and the process continues
- Termination: The ribosome reaches a stop codon which will terminate the production of the protein; the protein is released
mRNA
A sequence of codons that is a complementary copy of a single gene; carries information from the DNA to the ribosome
tRNA
Brings a specific amino acid to the mRNA and ribosome during translation:
- Sequence of three nucleotides (anti-codon) complementary to the codon foud of the mRNA
- Charged when specific amino acid is attached
Erythromycin
An antibiotic that binds to the 50S ribosomal subunit, inhibiting protein synthesis
Operon
Group of linked genes whose expression is controlled as a single unit
End Product Represssion
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 and off)