Chapters 7 + 8 Microbio flashcards

DNA is a double-stranded structure composed of a chain Deoxynucleotide subunits 

• Each nucleotide contains a 5-carbon sugar

• Phosphate group 

• 4 different nucleotides AT GC 

RNA is also composed of nucleotides 

• Ribose sugar 

• Phosphate group 

• Contains oxygen atom 

• AU GC 

• Shorter, linear single-stranded 

2 Tasks to be completed to multiply

1. Replication: Double-stranded DNA must be duplicated for information to be encoded to be passed on 

2. Gene Expression: The encoded information must be decoded so it can be synthesized

   1. Transcription: DNA information is encoded, copied and changed to RNA 

   2. Information carried by RNA and interpreted and synthesized to encode protein 

Origin of Replication in prokaryotes = the point at which DNA opens up  

DNA is semiconservative; each strand acts as a template for synthesis of a new complementary strand 

• 1 starting molecule to 2 daughter molecules 

• New DNA is made by DNA polymerase 

  • Leading stand is read 5 prime to 3 prime (continuous pieces) 

  • Lagging strand is read 3 to 5 or backwards (small pieces) 

    • Forms in okazaki fragments 

• A primer or short stretch of nucleotides is required to start making a DNA chain 

  • RNA primase starts the action of the primer 

• A DNA molecule lacking the proper sequence will not replicate 

• The proteins that bind to the bacterial origin of replication are the DNA gyrase and helicases 

  • Enzymes breaks the DNA helix at the site 

  • The region is exposed and acts as a template 

DNA Primase: Synthesize the RNA primers complimentary to the exposed template 

DNA ligase: glue to attach the Okazaki fragments. Also repairs irregularities or breaks. 

1. Seals repairs in the DNA 

2. Seals recombination fragments. For example, a repair is made where an entire segment is cut out, so it will have to repair that stretch of information.  

3. Connects Okazaki fragment 

DNA topoimerase: relieving the coiling of the double-stranded DNA. Stretches out the DNA so the helicase can do it’s work 

DNA-Binding proteins: Attach to the DNA 

• Bind to single- or double-stranded DNA 

• Involved in transcription, packaging, rearrangement, replication, and repair 

Helicases: Opens the DNA helix by breaking hydrogen bonds between the nitrogenous bases

• Begins at the site of origin and creates a replication fork by separating the two sides of the parental DNA 

• Stretch the DNA into single strands to be copied 

Primer RNA: initiates DNA synthesis. Required for dna synthesis because DNA polymerase needs to initiate polynucleotide synthesis 

• RNA primers are used by all living organisms. 

DNA polymerase requirements 

• Always needs a template 

• Can only add nucleotides to the 3’ end 

• Require a pre-existing chain or primer 

• Proofread and check their work and correct incorrect nucleotides

The 3 DNA polymerases 

1. DNA Polymerase I 

   1. Proofreading 

   2. In the lagging strand, will fill up any gaps between oazaki fragments 

2. DNA Polymerase II 

   1. Proofreading

3. DNA polymerase II 

   1. DNA polymerase III is most important because it’s required for DNA synthesis. 

Codon: A triple sequence of DNA and RNA that corresponds to a specific amino acid

Start codon and stop codon 

Anticodon: A section of transfer RNA (tRNA) is a categorization of 3 bases that are corresponding to codons in messenger RNA (mRNA). 

• The function of anticodons is to take the correct amino acids together to create a protein based on the instructions carried in the mRNa. 

Control of Gene Expression in Prokaryotes 

Positive Control of Lac-Operon

Inducer (operator): A small molecule that will bind to the repressor and block the RNA polymerase from transcribing 

• Will cause the

Promoter: Looking for a specific DNA sequence where the polymerase will bind to start transcription 

Negative Control 

Repressors: Repressing proteins the action of the promoter (bind to the DNA to prevent transcription, block the DNA polymerase from accessing the gene) 

The gene expressed will bind to the repressor and unable to bind to the operator and 

Operon: Group that regulate genes 

Chapter 8: Microbial Genetics 

Genetic changes in bacteria happens by 2 mechanisms

1. Mutations (Vertical gene transfer)

   1. Change the nucleotide sequence of the cell’s DNA. the daughter cell is altered from the parent cell. 

   2. Spontaneous mutations are random mutations that occur as a part of normal cell division. Every large population has mutants. 

2. Horizontal Gene transfer 

   1. Transfer/movement of DNA through conjugation 

Genotype: Genetic makeup of the cell 

Phenotype: Observable physical properties of an organism. This include the organism's appearance, development, and behavior 

DNA Repair 

Specific Repair: Targets a single kind of lesion in DNA and repairs only that damage 

Nonspecific: Use a single mechanism to repair multiple kinds of lesions in DNA 

• 3 steps 

  • Recognition of damage 

    • When DNA polymerase does the proofreading and something is wrong 

  • Removal of damaged region 

  • Resynthesis using the information on the undamaged strand as a template 

Base substitution mutations are the most common type of mutation and occurs during protein synthesis when there is an incorrect nucleotide. 

• 1 base pair changing is a point mutation 

• SIlent 

  • Change in the sequence of nucleotide bases which constituted DNA, without a subsequent change in the amino acid or funciton of the protein 

• Missense 

  • Change in one DNA base pair that results in the substitution of the amino acid for another in the protein made by a gene 

• Non-sense 

  • A change in one base pair but instead of making another protein there will be a signal for the cell to stop building a protein. 

    • Results in a shortened protein that can’t 

• Frameshift mutations: Occurs with the addition or loss of DNA bases changes the genes reading frame. 

  • Insertion: Changes the number of DNA bases by adding a piece of DNA. The protein may not allow the gene to function properly. 

  • Deletion: Changes the number of DNA bases by removing a piece fo DNA.

  • Duplication: consisting of a piece of DNA that is abnormally copied one or more times. This may alter the function of the resulting protein. 

• Induced Mutation: genetic mutations that occur due to influences outside the cell. The agent causing the mutation is a mutagen. 

  • Chemical mutagens can cause base substitutions, and others cause frameshift mutations. 

    • Base analogs: are molecules which have very similar structure to one of the 4 bases in DNA 

      • Thymine dimers: distort the shape of the DNA molecule. The molecule can’t fix properly into the double heli. 

      • If not repaired the cell will die. 

• Trasposons: Jumping genes or pieces of DNA that move from one location to another in a cell’s genome 

• Transposition is the process where the jumped gene is inactivated. This disrupts the function of the gene 

Repairs of Errors in Nucelotide Incorpoation 

• DNA polymerase incorporates the wrong nucleotide as it replicates DNA. 

  • Proofreading and mismatch repair

    • Proofreading: Enzymes back up and excise a nucleotide not correctly bonded 

    • Mismatch repair: Fixes errors missed by the proofreading 

      • Specific protein bind to the site of the mismatch nucleobase