Micro lecture ch8

genetics-the study of what genes are, how they carry info, how info is expressed, and how genes are replicated

genome-the entire genetic makeup of an organism including both its genes and noncoding sequences that link these

chromosome-naked, circular peice of DNA containing approx. 3000-4000 genes

gene-a segment of DNA that encodes a functional product, usually a protein

genetic code-the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein

genotype-an organism's genetic makeup, the info that codes for all particular characteristics of that organism; represents potential properties, but not the properties themselves

phenotype-actual, expressed properties, such as the organism's ability to perform a particular chemical reaction; manifestation of genotype

genomics-the sequencing and molecular characterization of genomes

• the structure of DNA helps explain two primary features of biological info storage.
• first, the linear sequence of bases provides the actual info
• genetic info is encoded by the sequence of bases along the strand of DNA, in much the same way as our written language uses linear sequence of letters to form words and sequences

• 1. the double helix of the parental DNA separates as weak hydrogen bonds between the nucleotides on opposite strands break in response to the action of replication enzymes
• 2. hydrogen bonds form between new complementary nucleotides and each strand of the parental template to form new base pairs
• 3. enzymes catalyze the formation of sugar-phosphate bonds between sequential nucleotides on each resulting daughter strand

In the process of transcription, genetic info in DNA is copied, or transcribed, into a complementary base sequence of RNA. The cell then uses the info encoded in this RNA to synthesize specific proteins thru the process of translation.

• 1. Regulating protein synthesis at the gene level is energy-efficient because proteins are synthesized only as they are needed.
• 2. Constitutive enzymes produce products at a
• fixed rate. Examples are genes for the enzymes in glycolysis.
• 3. For these gene regulatory mechanisms, the
• control is aimed at mRNA synthesis.

• Repressionand Induction
• 4. Repression controls the synthesis of one or
• several (repressible) enzymes.
• 5. When cells are exposed to a particular
• end-product, the synthesis of enzymes related to that product decreases.
• 6. In the presence of certain chemicals
• (inducers), cells synthesize more enzymes. This process is called induction.

• A base substitution (or point mutation) occurs when one base pair in
• DNA is replaced with a different base pair.

• Alterations in DNA can result in missense
• mutations (which cause amino acid substitutions) or nonsense mutations (which create stop codons).

In a frameshift mutation, one or a few base pairs are deleted or added to DNA.

Mutagens are agents in the environment that cause permanent changes in DNA.

Spontaneous mutations occur without the presence of any mutagen

Methylases-these enzymes add a methyl group to selected bases soon after DNA strand is made. a repair endonuclease then cuts the nonmethylated strand

agents in the environment, such as certain chemicals and radiation, that directly or indirectly bring about mutations

• the mutation rate is the probability that a gene will mutate when a cell divides. The rate is usually stated as a power of 10, and bc mutations are very rare, the exponent is always a neg. number.
• A mutagen usually increases the spontaeous rate of mutation, which is about one in 10⁶ replicated genes, by a factor of 10 to 1000 times

the exchange of genes between two DNA molecules to form new combinations of genes on a chromosome

• bacteria can pass their genes not only to their offspring (vertical gene transfer), but also laterally, to other microbes of the same generation
• (horizontal gene transfer)

plasmids are self replicating, gene-containing circular pieces of DNA about 1-5% of the bacterial chromosome.

not usually essential for the cell’s survival

There are several types of plasmids, including conjugative plasmids, dissimilation plasmids, plasmids carrying genes for toxins or bacteriocins, and resistance factors.

natural selection will act on diverse populations to ensure the survival of those fit for that particular environment. the different kids of microorganims that exist today are the result of a long history of evolution

genetics-the study of what genes are, how they carry info, how info is expressed, and how genes are replicated

genome-the entire genetic makeup of an organism including both its genes and noncoding sequences that link these

• chromosome-naked, circular peice
• of DNA containing approx. 3000-4000 genes

gene-a segment of DNA that encodes a functional product, usually a protein

Deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information

genetic code-the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein

phenotype-actual, expressed properties, such as the organism's ability to perform a particular chemical reaction; manifestation of genotype

the synthesis of a complementary strand of RNA from a DNA template

protein synthesis is called translation bc it involves decoding the "language" of nucleic acids and converting that info into the "language" of proteins

groups of 3 nucleotides

a change in the base sequence of DNA

• aka point mutation
• most common type of mutation involving single base pairs
• a single base at one point in the DNA sequence is replaced with a different base

if the base substitution results in an amino acid substitution in the synthesized protein

• by creating a nonsense (stop) codon in the middle of an mRNA molecule
• when some base substitutions effectively prevent the synthesis of a complete functional protein; only a fragement is synthesized

• changes in DNA in which one or a few nucleotide pairs are deleted are inserted in the DNA
• can shift the "translational reading frame"-that is, the three-by-three grouping of nucleotides recognized as codons by the tRNAs during translation

occurs in the absence of any mutating-causing agents

agents in the environment, such as certain chemicals and radiation, that directly or indirectly bring about mutations

a process where genes are transferred from one bacterium to another as "naked" DNA in solution

• another mechanism by which genetic material is transferred from one bacterium to another
• mediated by one kid of plasmid
• differs from transformation in two major ways:
• conjugation requires direct cell-to-cell contact
• second, conjugating cells must generally be of opposite mating type; donor cell smust carry the plasmid, and recipient cells usually do not

bacterial DNA is transferred from a donor cell to a recipient cell inside a virus that infects bacteria, called a bacteriophage, or phage

circular peice of DNA that replicates independently from the cell's chromosome

• Resistance factors are plasmids that have significant medical importance
• R factors carry genes that confer upon their host cell resistance to antibiotics, heavy metals, or cellular toxins
• contains two groups of genes:
• resistance transfer factor (RTF) and includes genes for plasmid replication and conjugation
• r-determinant, that has the resistance genes; it codes for the production of enzymes that inactivate certain drugs or toxic substances