MicroBio Chapter 9

Polymers of repeating units- composed of three smaller units.

• DNA contains everything but uracil
• RNA contains everything by thymiine

Basic unit of DNA stucture: composed of phosphate, deoxyribose sugar, and nitrogenous base.

• Purines: Adenine (A) & Guanine (G)
• Pyrimidines: Thymine (T) & Cytosine (C) & Uracil (U)

• Purines: Two rings of nitrogen base
• Pyrimidines: One ring

• DNA contains all nitrogen bases except uracil
• RNA contains all nitrogen bases except thymine
• RNA is a single strand containing ribose sugar instead of deoxyribose, and uracil instead of thymine.
• DNA is a double-helix, sugar-phosphate backbone represents the rails and paired nitogen bases represent the steps.

• mRNA: Messenger RNA is transcribed from DNA and is translated=code to make protien. It is the sequence of amino acids in a protien
• tRNA: is needed for translation, and carries amino acid to ribosome, is transcribed from DNA
• rRNA: major component of ribosomes, is transcribed from DNA. forms the major part of a ribosome and participates in protien synthesis.

• Sum total of genetic material of a cell.
• Genomes of cells are composed exclusively of DNA

• A discrete cellular structure composed of a neatly packaged DNA molecule.
• Chromosomes of all cells are subdivided into basic information packets called genes.

• Site on the chromosome that provides information for a certain cell function.
• It is a certain segment of DNA that contains the necessary code to make a protien or RNA molecule.
• Three basic categories of genes.
• Structural genes: code for protien
• RNA coding genes: code for RNA
• Regulatory genes: control gene expression

• Sum of all types of genes that constitutes an organisms destinctive genetic makeup
• The expression of the geneotype creates traits reffered to as the phenotype
• Phenotypes can change depending on which genes are turned on

• Eukaryotic Chromosomes: DNA molecule tightly wound around histone proteins
• -located in the nucles
• - vary in # from few to hundreds
• -can occur in pairs (diploid) or singles (haploid)
• -appear linear
• Prokaryotic chromosomes: condensed and secured into a packet
• -single: circular double stranded chromosome

The paired nitrogenous bases are aligned as to be joined by hydrogen bonds. These weak bonds can be easily broken by Helicase.

• For the language of the DNA to be preserved for a very long time.
• Duplicated and passed on to offspring
• It occurs in binary fission -the metabolic machinery of a bacterium initiates the duplication of the chromosome.

• 1. Nucleotides are buried deep, so the DNA molecule must be unwound & two strands of helix seperated from each other
• 2. DNA Polymerase is unable to begin synthesizing a chain of nucleotides, but can only continue to add nucleotides to an already existing chain.
• 3. Can only add nucleotides in one direction, from 5'-3'

• Leading Strand: continuous, complete strand 5'-3'
• Lagging Strand: goes from 3'-5'. DNA polymerase adds nucleotides few at a time, in direction ---> away from fork.
• Okazaki Fragments: 1 Strand containing short fragments and are connected by the enzyme ligase.

• It can correct the mistakes made
• the incorrect unmatching bases, excise them, and replace them with the correct base

• The stored information of DNA is converted to RNA molecules which carry out instructions. Genetic information flows from DNA to RNA to protein.
• The master code of DNA is first used to sinthesize an RNA molecules via transcription, and the information used to produce protiens is known as translation.

• Proteins primary structure, order, and type of amino acids in the chain determines its charateristic shape & function.
• Protiens ultimatley determine phentotype, expression of all aspects of cell function/structure.
• DNA is mainly a blueprint that tells cells which kinds of protiens and RNA to make & how.

• mRNA: the copy of structural genes in DNA
• the message of this transcribed strand is later read as a series of triplets called Codons.
• tRNA: uniform in length, tRNA is a copy of specific region in DNA
• contains sequences of bases that form hydrogen bonds with complimentary sections of the same tRNA strand. converts RNA language into protien language.

• rRNA: the ribosomal RNA and protien-long polynucleotide molecule
• 2 subunits: engage in final translation of genetic code

• Takes a gene on DNA and converts it into a strand of RNA
• RNA Polymerase: huge enzyme system converting DNA code to RNA.
• Transcription is initiated when RNA polymerase recognizes the segent of DNA called promoter region. Its allowed to begin when DNA helix begins to unwind @ second sequence.
• As polymerase advances & synthesizes RNA molecule complimentary to temperate strand of DNA

5'-3' mRNA is assembled by addition of nucleotides complimentary to DNA temperate strand.

Polymerase gets another signal that signals seperation and release of mRNA strand now called the transcript.

• Particular amino acid can be coded for by more than a single codon. SO
• One cannot predict from protein structure what the exact mRNA codons are because of redundancy.

thought to permit some variation or mutation without altering the message.

• Because the prokaryotes do not contains a nucleus holding the DNA.
• The mRNA transcript does not have to pass through pores in the nuclear membrane

• Coordinated sets of genes, all regulated as a single unit.
• They are either inducible or repressible
• The category they fall into is determined by how transcription is affected by the envoirnment surrounding the cell.

• Catabolic operons: are inducible oprerons that are turned on by the substrate of the enzyme needed for which the structural genes code
• Repressible operons: contains genes for coding anabolic enzymes

• 1. Regulator: composed of the gene that codes for a protein capable of repressing the operon.
• 2. the control locus: promoter and the operator acts as an on/off switch for transcription
• 3. Structural locus: made up of three genes each coding for a different enzyme needed to catabolize lactose

• Lac operon only functions in the absense of glucose or if the cells energy needs are not being met by the available glucose
• When glucose is present, a second regulatory system ensure that the lac operon is inactive, regardless of lactose levels.

• SPONTANEOUS: random change in DNA arising from errors in replication that occur randomly
• INDUCED: result from exposure to known mutagents, which are primarly physical or chemical agents that interact with DNA in a distruptive manner

Addition, deletion, or substitution of single bases

• Any change in the code that leads to placement of a different amio acid
• it can create a fault nonfunction protein
• it can produce a protein that functions in a different manner
• cause no significant alteration in protein function

• Changes a normal codon into a stop codon that does not code for an amino acid and stops the production of the protein
• Always results in a nonfunctional protien

Alters the base but does not change the amino acid, thus having no effect.

When a gene that has been mutated or undergone mutation reverses (mutates back) to its original base composition

• One or more bases are inserted into, or deleted from a newly synthesized DNA strand.
• The reading frame of the mRNA has been changed
• Nonfunctional protein=result

• Bacterial "sex"
• Plasmid or other genetic material is transferred by a donor to a recepient cell

• Transfer of naked DNA and requires no special vehicle
• From enviornment

DNA transfer mediated through the action of a bacterial virus!

• In gram - cells, donor has the plasmid (Fertility or F factor) that allows the synthesis of a conjugative pilus.
• A cells role in the conjugation is denoted by F+ factor for the cell that has the plasmid
• F- for cell that doesn not

Cells can transmit its chromosomal genes at a higher frequency than other cells.

The F factor can direct a more comprehensive transfer of part of the donor chromosome to a recipient cell.