Chapter 14 - Bio

The Central Dogma One gene - one polypeptide // Beadle and Tatum The Central Dogma - cells are governed by a cellular chain of command

The Flow of Genetic Information Gene expression - the process by which DNA directs protein synthesisDNA - TRANSCRIPTION - RNA - TRANSLATION - PROTEIN ----------------------> -------------------->

Basic Principles of Transcription synthesis of RNA under the direction of DNA produces messenger RNA (mRNA)

Basic Principles of Translation synthesis of a polypeptide, which occurs under the direction of mRNA Ribosomes are the sites of translation

RNA The bridge between DNA and protein synthesis RNA has ribose sugar and the base uracil (U) rather than thymine (T) usually single stranded TEMPLATE DNA 5' - ACCTAGTTGC - 3'Trascription RNA 3' - UGGAUGAACG - 5'

Molecular Components of Transcription RNA polymerase Promoter Terminator in bacteria Transcription

Transcription in Eukaryotes Occurs in the nucleus RNA processing produces the mature mRNA mRNA goes to the cytoplasm for translation on ribosomes

RNA Processing WHEN - modify pre mRNA before genetic messages are dispatched to the cytoplasm WHERE - nucleus Two types of modifications: "Capping and Tailing" - both ends of the primary transcript are altered "Splicing" - interior parts of the molecule are cut out and other parts are spliced together

Functions of Altercations of mRNA ends facilitates the export of mRNA to the cytoplasm protects mRNA from hydrolytic enzymes helps ribosomes attach to the 5' end

often translation isn't sufficient to make a functional proteinpolypeptide chains are modified after translation or targeted to specific sites in the cell

Protein FoldingDuring synthesis, a polypeptide chain spontaneously coils and folds into its 3D shape

Post - Translational ModificationsProteins may also require this before doing their jobs Attach sugar, lipids, phosphate groups to certain amino acids one or more amino acids are removed from the leading end of the polypeptide chain a polypeptide chain is cleaved into multiple pieces Multiple polypeptide assemple a protein that has quaternary structure

Targeting Polypeptides to Specific Locations Two populations of ribosomes are evident in cells: free ribosomes (in the cytosol) and bound ribosomes (attached to the ER) Free ribosomes mostly synthesize proteins that function in the cytosol Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell Polypeptide synthesis always begins in the cytosol synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER Polypeptides destined for the ER or for secretion are marked by a signal peptide A signal-recognition particle (SRP) binds to the signal peptide

Making Multiple Polypeptides In bacteria and eukaryotes multiple ribosomes translate an mRNA at the same time Once a ribosome is far enough past the start codon, another ribosome can attach to the mRNA Strings of ribosomes called polyribosomes (or polysomes) can be seen with an electron microscope

Transcription in ProkaryotesAbsence of a nuclear membrane mRNA transcription and translation are coupled translation of mRNA can begin before transcription has finished mRNA is translated as soon as it is made no processing

Mutations mutations - changes in the genetic material of a cell or virus small scale mutations - chemical changes in just one or a few nucleotide pairs of a gene the change of a single nucleotide (point mutation) in a DNA template strand can lead to the production of an abnormal protein

Types of Small-Scale MutationsSmall scale mutations within a gene can be divided into two general categories Nucleotide-pair substitutions. A nucleotide-pair substitution replaces one nucleotide and its partner with another pair of nucleotides One or more nucleotide-pair insertations or deletions (frameshift mutations)

Substitutaions Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code Missense Mutations still code for an amino acid, but not the correct amino acid. Substitution mutations are usually missense mutations Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Insertations and Deletions inserations and deletions are additions or losses of nucleotide pairs in a gene These mutations have a disastrous effect on the resulting protein more often than substitutions do Insertion and deletion of nucleotides may alter the reading frame of the genetic message, producing a frameshift mutation