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prof.Kan chpt 8


Genetics study of the inheritance or heredity.
Genome total genetic information in an organism
Chromosome: structures that contain the DNA of organism.
Gene: fundamental unit of a chromosome.
Genetic Code: A sequence of three bases in DNA.
Codon: a sequence of three bases in mRNA that specifies a particular amino acid in the translation process.
Genotype: genetic makeup of an organism.
Phenotype: expression of the genes; characteristics that can be observed.
DNA and Chromosome Bacteria contain a single circular chromosome made of DNA. A typical bacteria chromosome has about 4 million base pairs and is about 1mm long (1000 times larger than the bacterial cell).
Structure of DNA (Deoxyribose Nucleic Acid) A. DNA is a bouble stranded helical polymer of nucleotides.
Structure of DNA (Deoxyribose Nucleic Acid) 1. Pentose sugar (Deoxyribose) 2. Phosphate and 3. One of the following four nitrogen bases:
four nitrogen bases: A. Purines: a. Adenine b. Guanine B. Pyrimidine: a. Cytosine b. Thymine
B. Each nucleotide is composed of: C. Two strands are held together by hydrogen bonds. D. Thymine is always paired with adenine, and guanine is always paired with cytosine (complementary base pairing).
Structure of RNA 1. Single stranded. 2. Contains ribose sugar instead of deoxyribose sugar. 3. The nitrogen bases include: A. Purine a. Adenine b. Guanine B. Pyrimidine a. Cytosine b. Uracil
4. Bacterial cells contain four different types of RNA 1. Messenger RNA (mRNA) 2. Ribosomal RNA (rRNA) 3. Transfer RNA (tRNA) 4. Ribozymes
DNA Replication - Lag Phase -Making copies 1.DNA Molecule uncoils. 2.Hydrogen bonds between base pairs break. This allows the parent strands to serve as templates.DNA –polymerase 3.Replication occurs on both strands simultaneously.4.DNA replication is semi conservative. (50% new and 50old)
The Flow of Genetic Information 1. Proteins are polymer of amino acids and are essential for the survival of all living cells. 2. The genetic code (codon) in a mRNA molecule gives the amino acid sequence for a protein. DNA –polymerase add a new neuclitide to the old strands.
The Flow of Genetic Information 3. There are 64 possible codons (61 sense and 3 nonsense (UAA, UAG, UGA) that code for 20 amino acids. Sens are amino acid attached and the 3 no amino acid attached.
The Flow of Genetic Information 4.The genetic code is redundant;means there is more than one codon for each amino acid, except for tryptophane(UGG) and methionine(AUG)which have only one code word each. 5. The genetic code that initiates the message is AUG, which codes for methionine.
Protein Synthesis The process of protein synthesis involves the following two major steps: (A) Transcription and (B) Translation
Transcription The synthesis of RNA (mRNA, tRNA, or rRNA) 1. This process requires supply of RNA nucleotides and enzyme RNA-Polymerase. 2. Only one strand of DNA called sense strand serves as the template for mRNA synthesis.
Transcription 3. RNA Polymerase (sigma factor) binds to promote site on sense strand of DNA andinitiates transcription. 4. The region of the DNA that signals the end for transcription is the terminator site.
Transcription 5. The DNA molecule recoils. 6. Newly synthesized mRNA goes to the ribosome.
Translation - Conversion of mRNA information into amino acid sequence (protein) at the ribosome. 30s subunit of the ribosomes have two specific sites on their surface
Conversion of mRNA information into amino acid sequence (protein) at the ribosome. A-Site: is the entry site for tRNA whose anticodon recognizes the codon on the mRNA. P-Site: is the exit site for naked tRNA, it also carries the growing polypeptide chain.
Translation 1. mRNA becomes associated with 30s subunit of the ribosome. 2. 50s subunit then joins the 30s subunit.
Translation 3. The ribosome (70s) then moves along mRNA, exposing the next codon.A peptide bond is then formed between the amino acids, and the ribosome moves again to expose the next codon and transfer the dipeptide to the P-Site.
Translation 4. Naked tRNA leaves the ribosome to pick up another amino acid. 5. A stop codon or non sense codon (UAA or UGA) signals the end of polypeptide chain.
Translation 6.Most ribosome that sequentially attach to a single mRNA. These complexes are called polyribosomes. 7. A typical polypeptide of 300 amino acids can be synthesized in about 20 seconds.
The Regulation of Bacterial Gene Expression - The Operon Model of Gene Expression An operon is a set of genes that regulate the synthesis of specific protein/enzyme.
An Operon is consists of: 1. Regulator Site 2. A Promoter Site: 3. An Operator Site: 4. Structural Genes:
1. Regulator Site codes for repressor protein which is always present in the cell.
2. A Promoter Site: the region of DNA where RNA polymerase binds.
3. An Operator Site: controls the transcription of structural genes.
4. Structural Genes: carry genetic information for specific proteins.
Inducible Operon a. Regulates the synthesis of digestive/catabolic proteins (enzymes) b. Repressor protein is active when synthesized but becomes inactive in the presence of inducer/substrate.
Inducible Operon c. When repressor becomes inactive, synthesis of digestive protein occurs. d. When the digestion of the substrate is completed, repressor becomes active again.
Repressible Operon a. Regulated the synthesis of synthetic (anabolic) proteins b. Repressor protein is inactive when synthesized but becomes active when synthetic protein binds with it. c. When repressor becomes active, it stops the synthesis of protein.
Mutations: Changes in the Genetic Material Mutation is defined as a permanent, heritable change in the DNA.
Causes of Mutations - Spontaneous Mutation: Spontaneous Mutation: A random change in the replication of DNA without any mutagen. Rate of this type of mutation varies from one in one million to one in one billion.
Induced Mutations: Occur in the presence of mutagens (chemical or physical agent that greatly increase the mutation rate over the rate of spontaneous mutation.
Types of Mutations - A. Point Mutation or Base Substitution It results from the substitution of one nucleotide for another. Ex:1. Codon AAU becomes AAC it would still code for amino acid asparagines. 2. Codon AAU becomes AAG it would code for lysine instead of asparagines. 3. In sickle cell anemia
B. Nonsense Mutation Base substitution produces a nonsense codon. Incomplete polypeptide is synthesized.
C. Fragmeshift Mutation One or a few nucleotides are deleted or added to the DNA.
Genetic Transfer and Recombination---- 1. Transformation A mode of genetic transfer in which a free DNA fragment (naked DNA) from one bacterial cell (the donor) is taken up by another (the recipient) and subsequently undergoes recombination with the recipient chromosome.
2. Conjugation A process in which DNA is transferred from one bacterium (the F+ or donor or male) to another (the F- or recipient or female) via physical connection (pilus) between two cells.
3. Transduction (The case of piggyback DNA).The transfer of bacterial genes from one bacterium to another by bacteriophage(virus which infects bacteria and joins with its DNA
Created by: rkasiejka