Chapter 8 (Microbial Genetics)
Terms in this set (65)
The Appearance of Life on Earth
Earth is 4.5 billion years old.
Fossil evidence shows Archaea and Bacteria have been present for 3.8 billion years.
Because of genetic variation, the prokaryotic domains have evolved to fill a variety of niches
Hereditary Molecule in All Organisms Is DNA
Genetics is the science of heredity; it focuses on the structure and expression of DNA.
Watson & Crick (1953)
DNA molecule is a double helix.
Based on X-ray studies by Rosalind Franklin.
Structure of DNA is the foundation of knowledge of DNA replication and gene expression
DNA is composed of repeating monomers called nucleotides:
Sugar deoxyribose + phosphate group + nucleotide.
Nucleotides are cytosine (C), guanine (G), adenine (A), and thymine (T).
Nucleotides on each side of the double helix pair up and form hydrogen bonds to hold the 3-D structure together.
C always pairs with G; A always pairs with T.
5' & 3' Prime
The 5' and 3' mean "five prime" and "three prime", which indicate the carbon numbers in the DNA's sugar backbone.
The 5' carbon has a phosphate (P) group attached to it
The 3' carbon has a hydroxyl (-OH) group.
This asymmetry gives a DNA strand a "direction"
A segment of DNA that forms a unit of heredity
The complete set of genes for an organism
Because the genome contains only one set of genes, prokaryotes are haploid (1)
-Information in the prokaryotic genome includes core genes, variable genes, and unique genes.
DNA within a Cell Is Highly Compacted
If the DNA were stretched out, it would be 500 times longer than its cell.
DNA is supercoiled around special proteins and then folded into loops.
Bacterial and archaeal DNA is organized within an area of the cytosol
The DNA usually exists as a single, highly compacted circular chromosome.
Many bacterial, archaeal, and fungal cells contain plasmids.
Plasmids carry nonessential but often useful information:
Resistance to antibiotics.
Resistance to heavy metal toxicity.
Production of proteins that inhibit other bacterial species.
is found in eukaryotic microbes containing mitochondria and/or chloroplasts.
Contains genes for organelle reproduction and function.
among the Bacteria and Archaea Is Variable
A summary of DNA Replication
summary of board
Replication Basics. Replication depends on the pairing of bases between the two strands of DNA. .
DNA Replication (Part of Cell Cycle)
DNA replication is a highly regulated anabolic (requires energy to build) process that is nearly universal in living organisms.
Divided into three stages:
Following replication, 2 "daughter strands" of DNA exist:
Each of the two DNA double helices contains one old half and one newly built half.
Starts at oriC, the replication origin.
Helicase and other proteins unwind and separate DNA.
This forms the replication fork, where the process of building a new strand begins.
DNA polymerase synthesizes new nucleotide strands of DNA on old template using complementary bases.
DNA polymerase only reads in the 3' to 5' direction.
Leading strand is synthesized continuously; lagging strand is made in chunks later joined by ligase.
When the terminus region is reached, the process stops.
Produces RNA and Protein for Cell Function
is the overall process of using the information in genes to make proteins and other products.
The central dogma
identifies the flow of genetic material.
(DNA -> RNA -> protein)
oxygen is removed
(de oxygen) instead a hydroxyl
Ribonucleic acid is a polymeric molecule essential in various biological roles in coding, decoding, regulation, and expression of genes.
Differences between DNA & RNA
check chart on Slide 13 ch.7
copies genetic information from DNA into complementary RNA.
reads the information in RNA and uses it to synthesize protein.
is the enzyme responsible for transcribing DNA.
Transcription (RNA )
Copies Genetic Information into Complementary RNA
Divided into three stages:
RNA polymerase looks for the part of the gene called the promoter, where it attaches and unwinds the DNA.
RNA polymerase adds complementary bases to the DNA strand to make a product composed of RNA.
RNA polymerase stops transcribing at a terminator sequence.
Types of RNA
Play Roles in Gene Expression
mRNA (messenger RNA)
rNA (transfer RNA)
tRNA (ribosomal RNA)
Transcription product that carries message in codons to ribosome.
and proteins make up ribosomes.
carries anticodon complimentary to mRNA message and amino acid to ribosome for protein synthesis.
Regulatory RNAs control gene expression.
The Genetic Code `
Consists of Three-Letter Codons
The specific sequence of nucleotides transcribed into mRNA is called the genetic code.
Read in three-letter codons.
Only 20 possible amino acids called for by the codons.
There are 4 bases x 3 letters = 64 possible codes.
Some amino acids have multiple codons
Is the Process of Assembling a Polypeptide
To Make A Protein....
the ribosome must work with mRNA and tRNA to translate the language of the genetic code (carried by the mRNA) to the language of proteins (the amino acids carried by the tRNA).
will be transferred to a protein later on.
The ribosome clamps onto the mRNA at the start codon AUG.
The process continues until a stop codon is encountered on the mRNA, and the chain is released.
tRNAs base pair with the mRNA feeding through the ribosome, and the amino acids they carry are bound together with peptide bonds to form a chain.
Gene expression control
Because transcription is the first step leading to protein synthesis, one way to control the products a cell makes is to regulate transcription.
Regulation by "turning on" and "turning off" genes.
Jacob & Monod (1961)
Bacterial DNA is organized into transcriptional units called operons.
An operon consists of a regulatory gene, a promoter, structural genes, and a repressor.
A common means to control gene expression is by negative feedback when too much product serves as a repressor and turns off the gene.
Are Permanent Changes in a Cell's DNA
Mutations are the results of heritable changes in a genome.
Mutations can be spontaneous or induced:
point mutation is one of the most common results of mutagens acting on DNA.
One incorrect base in the mRNA sequence of codons.
No change in protein produced due to the redundancy of the genetic code.
The wrong amino acid is inserted at the point of the mutation, and the protein may not have the correct shape and function.
Stop codon at the point of the mutation; the polypeptide is nonfunctional.
Base-pair deletion or insertion
Leads to an inappropriate number of bases and a frameshift mutation, where the protein is built abnormally.
Attempt to Correct Mistakes or Damage in the DNA
Because DNA is double stranded, in case of mutation the undamaged strand can serve as a template to fix the damaged strand
Correction enzymes scan DNA for errors and cut them out. DNA polymerase inserts correct base.
Nucleotide excision repair
Enzymes detect distortions in DNA and remove the affected section.
Transposable Genetic Elements
Can Cause Mutations
discovered transposons in maize.
Insertion sequences and transposons move from one DNA location to another.
select for specific mutants or characteristics.
The Ames test
can identify potential mutagens.
cause revertants seen on medium lacking histidine
is used to detect nutritional mutants that fail to grow on minimal media when plated on complete nutritional medium.
Positive Selection of Mutants
Shows Resistant Organisms Growing on Minimal Medium