Unit 4 Genetics Ch. 12 DNA & RNA

Griffith & Transformation Griffith injected mice with 4 different samples of bacteria When injected separately, neither heat-killed (disease-causing bacteria), nor live, (harmless bacteria) killed the mice

Griffith & Transformation The 2 types injected together, however, caused fatal pneumonia From this experiment, biologists concluded (inferred) that genetic info. could be transferred from 1 bacterium to another

Griffith’s Experiment

Griffith & Transformation Transformation - when 1 strain of bacteria is changed by a gene or genes from another strain of bacteria

Avery & DNA Avery & other scientists performed experiments to determine if transformation required just 1 particular molecule (of a gene) Discovered that the nucleic acid, DNA, stores & transmits genetic info. from 1 generation of an organism to the next

The Hershey-Chase Experiment Studied viruses, nonliving particles smaller than a cell, that can infect living organisms Bacteriophage - virus that infects bacteria

The Hershey-Chase Experiment They performed experiments with a bacteriophage to determine its genetic material They concluded that the genetic material of the bacteriophage was DNA & not protein

The Hershey-Chase Experiment

The Components & Structure of DNA Genes were known to do 3 specific things: Carry info. from 1 generation to the next Put that info. to work by determining heritable characteristics of organisms Be easily copied, since all of a cell’s genetic info. is replicated every time a cell divides

The Components & Structure of DNA DNA is a long molecule made up of units called nucleotides Nucleotides - made up of 3 parts: A sugar A phosphate group A nitrogenous base

The Components & Structure of DNA Watson & Crick developed the model of DNA, a double helix, where 2 strands were wound around each other

The Components & Structure of DNA The 2 strands of DNA are held together by hydrogen bonds Those bonds only link adenine (A) & thymine (T), & guanine (G) & cytosine (C) Base-pairing rule - A - T, G - C

Structure of DNA

DNA & Chromosomes Most prokaryotes have a single circular DNA molecule in their cytoplasm

DNA & Chromosomes Eukaryotic DNA is located in the nucleus, in the form of a # of chromosomes The chromosome # varies from 1 species to another

DNA & Chromosomes Eukaryotic chromosomes have both DNA & protein, packed tightly together to form chromatin Chromatin - DNA that is tightly coiled around proteins (histones)

DNA & Chromosomes From largest to smallest, genetic information is arranged the following way: Chromosomes Genes (found on chromosomes) DNA (makes up genes)

DNA Replication Each strand of DNA could be used to make the other strand, they compliment each other Replication - when a cell’s DNA is copied

DNA Replication During DNA replication, the DNA molecule separates into 2 strands, then produces 2 new complimentary strands following base pairing rules Each strand of the double helix serves as a template, or model, for the new strand

DNA Replication DNA polymerase - enzyme that joins individual nucleotides to produce a DNA molecule It also proofreads each new DNA strand, to help prevent errors in copying the DNA

DNA Replication

RNA & Protein Synthesis Genes - coded DNA instruc. that control the production of proteins within the cell The 1st step in decoding the genetic messages is to copy part of the nucleotide sequence from DNA into RNA

The Structure of RNA There are 3 main differences between RNA & DNA: The sugar is a ribose, instead of deoxyribose RNA is single-stranded RNA contains the nitrogenous base uracil (U) instead of thymine (T)

Types of RNA There are 3 main types of RNA: Messenger RNA Ribosomal RNA Transfer RNA

Types of RNA Messenger RNA - (mRNA) - RNA molecules that carry copies of instructions for assembling amino acids into proteins They serve as “messengers” from DNA to the rest of the cell

Types of RNA Ribosomal RNA - (rRNA) - form of RNA that combines with proteins to make a ribosome

Types of RNA Transfer RNA - (tRNA) - RNA molecule that transfers each amino acid to the ribosome as it is specified by coded messages in mRNA

Types of RNA Transcription - process of producing RNA molecules by copying part of the nucleotide sequence of DNA into a complimentary sequence of RNA RNA polymerase - enzyme that works similarly to DNA polymerase

Types of RNA During transcription, RNA polymerase binds to DNA & separates the DNA strands RNA polymerase then uses 1 strand of DNA as a template to assemble nucleotides into a strand of RNA

Transcription

The Genetic Code Proteins are made by joining amino acids into long chains - polypeptides Each polypeptide has a combination of any 20 different amino acids

The Genetic Code Codon - 3 consecutive nucleotides that specify a single amino acid to be added to the polypeptide

The Genetic Code For ex.: UCGCACGGU Read 3 at a time: Which represents amino acids: Serine-Histidine-Glycine

The Genetic Code

Translation Translation - (protein synthesis) -decoding an mRNA message into a polypeptide chain (protein) It takes place on ribosomes Before translation occurs, mRNA is transcribed (re-written) from DNA in the nucleus & released in the cytoplasm

Translation Translation then begins when an mRNA molecule in the cytoplasm attaches to a ribosome As each codon of mRNA moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA

Translation Each tRNA molecule has an anticodon - 3 nitrogenous bases that are complimentary to 1 mRNA codon The ribosome attaches 1 amino acid to another, forming the polypeptide chain, until it reaches the “stop” codon

Translation After the amino acid is attached, the tRNA molecule that brought it into the ribosome, is released back into the cytoplasm The result is a protein

Translation

Translation

Summary: Role of RNA & DNA Start with a single strand of DNA That DNA is transcribed into RNA The RNA is separated into codons The codons code for amino acids, which form a polypeptide chain

Genes & Proteins Many proteins are enzymes that catalyze & regulate chemical reactions Genes for proteins can regulate the rate & pattern of growth throughout an organism Proteins are microscopic tools that are designed to build or operate a living cell

Mutations Mutations - a mistake in the DNA base sequence, may occur during copying the DNA Changes in the genetic material

Kinds of Mutations Gene mutations are changes in a single gene Chromosomal mutations are changes in the whole chromosome

Gene Mutations Point mutations - change in 1 or a few nucleotides, they occur at a single point in the DNA sequence Frameshift mutations - adding or deleting a nucleotide, shifts the “reading frame” of the genetic message

Chromosomal Mutations There are 4 types of chromosomal mutations: deletions, duplications, inversions, & translocations Deletions involve the loss of all or part of a chromosome Duplications produce extra copies of parts of a chromosome

Chromosomal Mutations Inversions reverse the direction of parts of chromosomes Translocations occur when part of one chromosome breaks off & attaches to another

Significance of Mutations Mutations cause changes in protein structure or gene activity They are the cause of many genetic disorders Some are associated with many types of cancer

Eukaryotic Gene Regulation Genes that code for liver enzymes are not expressed in nerve cells Cell specialization requires genetic specialization, but all cells in a multicellular organism carry the complete genetic code in their nucleus