Ch. 10-11 Biochem of the Genome/Mechanics of Microbial Genetics

Genetics

Genetics is the branch of biology that deals with the study of genes, genetic variation, and heredity in organisms. It focuses on how traits and characteristics are inherited, how they are passed from one generation to another, and how they are expressed in the organism's phenotype.

Genetic information transfer

Genetic information is passed through DNA in cells. The key molecules involved are DNA, RNA, and proteins. DNA carries the genetic information, RNA mediates transcription and translation, and proteins perform various functions.

Structure of DNA

DNA is a double-stranded helix composed of nucleotides. The bases are Adenine (A) and Thymine (T) which form 2 hydrogen bonds, and Cytosine (C) and Guanine (G) which form 3 hydrogen bonds.

Orientation of DNA strands

The strands of DNA run anti-parallel, meaning one strand runs 5' to 3' and the other 3' to 5'. Purines are Adenine (A) and Guanine (G), while Pyrimidines are Cytosine (C) and Thymine (T).

Semi-conservative replication

DNA replication is called semi-conservative because each new DNA molecule consists of one strand from the original DNA molecule and one newly synthesized strand.

Origin of replication

The origin of replication is the specific location on the DNA where replication begins. A replicon is a segment of DNA replicated from a single origin.

Enzymes in replication

Enzymes involved in replication include helicase, DNA polymerase, primase, ligase, and topoisomerase.

Leading and lagging strand synthesis

Leading strand synthesis occurs continuously, while lagging strand synthesis occurs discontinuously with Okazaki fragments. Okazaki fragments are short DNA segments synthesized on the lagging strand.

End of replication

Replication ends when the replication fork reaches the end of the DNA. Mistakes are corrected by DNA polymerase through proofreading and exonuclease activity.

Transcription

Transcription is the process of synthesizing RNA from a DNA template. Replication is the process of copying DNA.

Location of transcription and replication

Transcription occurs in the nucleus (eukaryotes) or cytoplasm (prokaryotes), while replication occurs in the nucleus (eukaryotes) or cytoplasm (prokaryotes).

Differences between RNA and DNA

DNA is double-stranded, contains deoxyribose, and has thymine (T). RNA is single-stranded, contains ribose, and has uracil (U). Both are nucleic acids that carry genetic information.

Types of RNA

Types of RNA include mRNA (carries genetic information to ribosomes), tRNA (brings amino acids to the ribosome), rRNA (makes up ribosomes), and other types like snRNA and miRNA involved in RNA processing and regulation.

Start of transcription

Transcription starts when RNA polymerase binds to the promoter region of DNA.

Enzymes involved in transcription

RNA polymerase and transcription factors.

Direction of RNA synthesis

RNA is synthesized in the 5' to 3' direction using the 3' to 5' DNA strand as a template.

Genetic code

The genetic code is a set of rules by which information encoded in mRNA is translated into proteins.

Codons

Codons are 3-nucleotide sequences in mRNA that correspond to specific amino acids or stop signals.

Number of codons

There are 64 codons, which specify 20 amino acids and stop signals.

Translation

Translation is the process of converting mRNA into a protein.

Key players in translation

Key players include ribosomes (which facilitate translation), tRNA (which brings amino acids), mRNA (which provides the code), and amino acids (the building blocks of proteins).

Ribosome assembly

Ribosomes consist of a large and small subunit, assembling around mRNA during translation.

tRNA arrangement

tRNAs bind at the A site and P site.

Stages of translation

Stages: Initiation (ribosome assembles), Elongation (amino acids are added), Termination (protein is released).

RNA processing

RNA processing involves adding a 5' cap, poly-A tail, and splicing out introns.

Exons

Exons are coding regions that remain in mRNA.

Introns

Introns are non-coding regions that are removed.

Gene regulation

Gene regulation ensures genes are expressed only when needed.

Lac operon

The Lac operon regulates lactose metabolism in bacteria.

Parts of the Lac operon

It consists of a promoter, operator, and structural genes.

Control of Lac operon

It is controlled by the lac repressor, which blocks transcription unless lactose is present.

Repressible operon

A repressible operon is one that is usually active but can be turned off by a repressor.

trp operon

The trp operon in bacteria is repressed when tryptophan is abundant.

Antibiotics targeting transcription

Antibiotics targeting transcription include rifampicin (inhibits RNA polymerase).

Antibiotics targeting translation

Antibiotics targeting translation include tetracycline, chloramphenicol, and erythromycin (which inhibit ribosomes).

Mutations

Mutations are changes in the DNA sequence, caused by replication errors, environmental factors, or viral infections.

Types of mutations

Types include point mutations (substitution, deletion, insertion), frameshift mutations, silent mutations, missense mutations, and nonsense mutations.

Mutation repair

Mutations are repaired by enzymes like DNA polymerase and ligase.

Role of mutations in evolution

Mutations contribute to evolution by introducing genetic variation, which can lead to beneficial traits being selected by natural selection.

Ames test

The Ames test detects mutagenic potential of a compound using Salmonella typhimurium.

Purpose of Ames test

It tests whether a substance causes mutations in bacterial DNA.

Bacterial recombination

Bacterial recombination is the exchange of genetic material between bacteria.

Plasmids

Plasmids are small circular DNA molecules.

Types of bacterial recombination

Types of recombination: transformation, transduction, and conjugation.

Transposons

Transposons are 'jumping genes' that can move within the genome.