1 GENETICS

2 Genetics is the study of heredity.Microbes are great tools for the study of genetics due to their small size, relative simplicity, and short generation times. DNA is the genetic material that is passed from a parent to its offspring or from a parent cell to the daughter cells.

3 Central Dogma (order of gene expression)DNA transcribed> RNA translated> proteins

4 Definitions and descriptions: Part IGenome - the total of the genetic material (DNA) of a cell. In prokaryotes, this genome is not contained within a nucleus but instead in a region of the cell called the nucleoid. Plasmids are also found in many bacteria, they are small circular pieces of DNA that are not part of the genome. In eukaryotes the nuclear genome is found within the nucleus. In addition, there is a small amount of DNA present in chloroplasts and mitochondria.

5 Definitions and descriptions: Part IIChromosomes are discrete structures composed of long, neatly packaged pieces of DNA and proteins. In prokaryotes the chromosome (usually n =1) is condensed and secured into a packet by basic proteins, is haploid, and is circular. In eukaryotes, the chromosomes (n = 3 to > 300) are haploid or diploid, tightly wound around histone proteins and linear.

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7 Definitions and descriptions: Part IIIGenes are the informational packets found on the chromosomes and they contain the template for proteins. Genes consist of pieces of DNA.

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9 Definitions and descriptions: Part IVThere are four nucleotide bases found in DNA. These bases consist of a sugar (deoxyribose) that is attached to a nitrogenous base [Adenine (A), Thymine (T), Cytosine (C), and Guanine (G)]. A and G are purine bases and C, T, and U are pyrimidine bases.

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11 Definitions and descriptions: Part VNotice that each of the bases on each of the strands of the double helix is joined together by sugar -phosphate bonds Notice also that the bases on each of the strands are also bonded. A always hydrogen bonds with T and C always hydrogen bonds with G We call these bases that are hydrogen-bonded base pairs. Because of these pairings, the two strands are complimentary but antiparallel.

12 DNA structure

13 The building blocks of DNA: Nucleotides

14 DNA replication: Part IThe duplication of DNA double helix prior to cell division DNA replication is Semiconservative

15 DNA replication: Part IIThe steps of replication are: Uncoiling. The double helix is tightly coiled and wrapped around proteins. Separation of the complimentary strands. The two strands of the double helix must be “unzipped” before replication can occur. 3. Synthesis of two new strands. The two new strands are synthesized by using both of the old strands as templates. New base pairings occur and basically then two complete double helices are the result.

16 DNA REPLICATION

17 DNA Replication video

18 Transcription In order for genes to be expressed, they must first be transcribed so that the information contained within the gene is transferred to RNA. The two other types of RNA are also transcribed.

19 TYPES OF RNA Messenger RNA

20 Transfer RNA

21 Ribosomal RNA

22 TRANSCRIPTION OVERVIEW

23 Transcription involves:1. Uncoiling of the chromosomes in the area to be transcribed. 2. Unzipping of the double strand in the area to be transcribed. 3. The synthesis of mRNA (messenger RNA) from the DNA template

24 Translation Translation is the process whereby mRNA serves a template for protein formation. Transfer RNA, plays a role in translation. Each tRNA contains a triplet anticodon and each anticodon associated with a particular amino acid. In addition, each anticodon is complimentary to a codon contained in mRNA.

25 Protein synthesis video

26 Although the basic processes are the same, transcription and translation differ between prokaryotes and eukaryotes. For example, eukaryotic mRNA contains introns which are spliced from the strand before translation. In addition, prokaryotes have no nucleus and thus transcription and translation can happen in the same area of the cell at approximately the same time whereas in eukaryotes transcription occurs in the nucleus and translation occurs in the cytoplasm (actually the RER).

27 POSTTRANSCRIPTIONAL PROCESSING

28 Viruses: Replication, Transcription, and Translation how do they do it?Unlike prokaryotes and eukaryotes, viruses are incapable of replication, transcription, and translation on their own. In general, the viral nucleic acid penetrates the host cell and is then introduced into the host’s machinery to synthesize new virus particles. How this occurs differs among the different types of viruses.

29 In dsDNA (double stranded DNA) viruses, the DNA enters the host’s nucleus and is replicated or transcribed into mRNA. These mRNA molecules are then translated into viral proteins. In some cases, the viral DNA becomes part of the host DNA by integrating itself into the host DNA. This may result in the formation of cancer cells. Examples of viruses that are known or suspected to be involved in the formation of cancer cells include: hepatitis B, herpesviruses, papilloma (wart) viruses, and adenoviruses.

30 Positive-sense single stranded RNA viruses are pieces of RNA that are ready to be translated in the cytoplasm of the host cell. Thus, they are similar to mRNA. However, these strands must also be reproduced, so a negative sense stand that is complimentary to the original strand is synthesized and then this serves as a template for the formation of many positive sense strands. Examples include poliovirus and hepatitis A virus.

31 RNA viruses with Reverse Transcriptase (AKA retroviruses) synthesize DNA using their RNA as a template and using reverse transcriptase. The enzyme directs the formation of a single stranded DNA molecule and the formation of the complimentary stand using the single stand of DNA as a template thus forming a dsDNA molecule This dsDNA molecule then enters the nucleus and is integrated into the host’s genome. An example of this type of virus is HIV.

32 Negative-strand ssRNA viruses must first be converted into a positive stand of RNA that serves as the master template for the formation of large numbers of negative strands and also as mRNA for the translation of proteins.

33 Regulation The metabolic activities of microbes (as well as all living organisms) must be regulated so that their needs are met without wasting energy producing unnecessary proteins. One way to regulate metabolism is to change the rate of synthesis of enzymes. Inducible enzymes are produced only when a signal molecule (e.g., a particular carbohydrate) is abundant. Repressible enzymes are produced in response to a scarcity of a signal molecule. Feedback inhibition is where the end product of a biosynthetic pathway directly inhibits the first enzyme in the pathway. However, some enzymes are unregulated and are produced at a constant rate (constitutively).

34 The Regulation of TranscriptionRegulation in prokaryotes primarily involves transcription. It usually involves a change in the frequency such that fewer mRNAs are produced. This type of regulation involves regulatory proteins that bind to specific regions of DNA (called operators) and interfere with the binding of RNA polymerase (an enzyme involved in the synthesis of mRNA). These regulatory proteins can either induce or repress the ability of RNA polymerase to bind to the operator. An example of transcription regulation is the Lac Operon

35 REGULATION: LAC OPERON

36 The regulation of TranslationThis is relatively rare. An example: Ribosomal proteins have two functions. One of these functions is the incorporation of the protein into the ribosome. The other function involves regulation where the protein binds to its own mRNA and thus inhibits translation when there is an excess of the protein present.

37 MUTATIONS Mutations are heritable changes in DNA Types: BeneficialHarmful (deleterious) Silent They can also be small (e.g., point) or large (e.g., deletions)

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39 GENETIC EXCHANGE IN BACTERIA

40 CONJUGATION

41 TRANSFORMATION

42 TRANSDUCTION

43 PLASMIDS