Microbiology Chapter on Genetics

The genetic code of an organism, represented by the sequence of nucleotides in its DNA. It defines the potential for traits to be expressed.

The observable characteristics of an organism, resulting from the expression of its genotype. These traits include appearance, behavior, and metabolic capabilities.

The flow of genetic information within cells, starting with DNA and ending with protein synthesis.

The process of creating an identical copy of the cell's DNA before cell division. This ensures each daughter cell receives a full set of genetic information.

The process of converting DNA's genetic code into a messenger RNA (mRNA) molecule. This mRNA carries the genetic instructions from DNA to the ribosome.

The process of using the mRNA sequence to synthesize a protein at the ribosome. Transfer RNA (tRNA) brings the corresponding amino acids based on the mRNA codons.

A set of genes that determine an organism's traits, including metabolic processes, structural components, reproduction, virulence, and antibiotic resistance.

The ability of microbes to resist the effects of antimicrobial agents, often due to mutations in genes that confer resistance.

The area of DNA synthesis where the double helix is unwound and separated into two single strands, creating a 'Y' shape.

The template strand is read in the 3' to 5' direction, and the new strand is synthesized in the 5' to 3' direction during DNA replication.

The strand of DNA that is synthesized continuously in the 5' to 3' direction, following the replication fork.

The strand of DNA that is synthesized discontinuously in the 3' to 5' direction, opposite to the direction of the replication fork, in short segments called Okazaki fragments.

Short segments of DNA that are synthesized on the lagging strand during replication, each starting with an RNA primer.

Short, single-stranded sequences of RNA that are necessary to initiate DNA replication.

An enzyme that unwinds the double-stranded DNA helix to create single-stranded regions.

Proteins that bind to single-stranded DNA and prevent it from re-annealing during replication.

An enzyme that alleviates the torsional strain ahead of the replication fork caused by the unwinding of the DNA.

An enzyme that synthesizes short RNA primers to provide a 3' hydroxyl group (–OH) for DNA polymerase to begin elongation.

An enzyme that adds new nucleotides to the 3' end of the primer, extending the new DNA strand in the 5' to 3' direction.

An enzyme that removes RNA primers and replaces them with DNA during replication.

An enzyme that seals the nicks between adjacent Okazaki fragments, creating a continuous strand.

The process of DNA replication involves unwinding the double helix, synthesizing short RNA primers, adding new nucleotides to the growing DNA strand, and sealing nicks in the backbone.

A region in DNA where RNA polymerase binds and initiates transcription.

The site of protein synthesis, where mRNA is translated into a polypeptide chain.

A molecule that carries an amino acid to the ribosome and matches it to the corresponding mRNA codon.

A three-nucleotide sequence in mRNA that codes for a specific amino acid.

A chain of amino acids linked together by peptide bonds, forming the building blocks of proteins.

The process by which genetic information is used to synthesize proteins, leading to observable traits.

Rearrangement of genetic material, occurring during sexual reproduction or in prokaryotes by horizontal gene transfer.

The specific site on a DNA molecule where replication begins. In prokaryotes, there is typically one origin, while eukaryotes utilize multiple origins along each chromosome.

DNA replication occurs in two directions, simultaneously from the origin.

The transmission of genetic material from parent to offspring during reproduction.

The transfer of genetic material between organisms, often of the same generation, without sexual reproduction. It is common in bacteria and can occur through transformation, conjugation, or transduction.

The process by which bacteria take up foreign DNA from their environment and incorporate it into their own genome. This involves DNA release, uptake of DNA, integration, and expression.

A type of horizontal gene transfer where genetic material is directly transferred between two bacterial cells through a conjugation pilus. It involves the formation of a pilus, DNA transfer, plasmid replication, and recipient incorporation.

One strand of the DNA, known as the coding strand or non-template strand. During transcription, RNA polymerase reads the non-coding strand in the 3' to 5' direction to synthesize complementary RNA.

A double-stranded molecule composed of deoxyribonucleic acid, with a sugar backbone made of deoxyribose and nucleotides (A, T, C, G). Stable and stores genetic information.

A single-stranded molecule made of ribonucleic acid, with a sugar backbone made of ribose. It contains the bases A, U (uracil), C, and G. Involved in protein synthesis and gene regulation.

DNA stores genetic information and is responsible for long-term information storage, while RNA serves as a template for protein synthesis (mRNA), is involved in the catalysis of biochemical reactions (ribozymes), and plays roles in gene regulation (e.g., miRNA, siRNA).

DNA is stable, double-stranded, and resistant to degradation, while RNA is more unstable due to its single-stranded structure and the presence of the 2'-hydroxyl group, which makes it more prone to hydrolysis.

A type of RNA that, along with proteins, makes up the ribosomes, which are the molecular machines responsible for protein synthesis in cells.

An enzyme that relieves tension and supercoiling ahead of the replication fork caused by the unwinding of the DNA.

Synthesizes short RNA primers that are required to initiate DNA synthesis.

The main enzyme that adds nucleotides to the 3' end of the primer, synthesizing the new DNA strand in the 5' to 3' direction.

Removes the RNA primers and replaces them with DNA nucleotides.

Joins the sugar-phosphate backbone of adjacent Okazaki fragments on the lagging strand by forming phosphodiester bonds.

Messenger RNA (mRNA) is a type of RNA that carries genetic information from the DNA in the nucleus (in eukaryotes) or the cytoplasm (in prokaryotes) to the ribosomes, where protein synthesis occurs. mRNA is synthesized through transcription from a DNA template and serves as a blueprint for building proteins during translation.

Transfer RNA (tRNA) is a type of RNA that plays a key role in protein synthesis by bringing amino acids to the ribosome during translation. Each tRNA molecule has a specific amino acid attached at one end and an anticodon at the other end, which is complementary to the mRNA codon. The anticodon enables the tRNA to recognize and bind to the corresponding codon on the mRNA, ensuring that the correct amino acid is added to the growing polypeptide chain. tRNA acts as an adaptor, matching mRNA codons with their respective amino acids during translation.

The promoter is a specific sequence of DNA located near the beginning of a gene. It acts as the binding site for RNA polymerase and other transcription factors that are necessary to initiate transcription. The promoter is typically located upstream (before) the coding region of the gene and defines the direction of transcription. In prokaryotes, the promoter usually contains consensus sequences such as the -35 and -10 regions (named for their approximate distance from the transcription start site), while in eukaryotes, the promoter often contains the TATA box, a similar conserved sequence.

The terminator is a specific DNA sequence that signals the end of transcription. Once RNA polymerase reaches the terminator sequence, it stops synthesizing RNA and detaches from the DNA template. In prokaryotes, terminators can be intrinsic (self-terminating) or involve the assistance of a protein called Rho. In eukaryotes, termination is more complex and often involves the cleaving of the newly synthesized RNA transcript and the addition of a poly-A tail.

Initiation involves the binding of RNA polymerase to the promoter, the unwinding of the DNA, and the beginning of RNA synthesis. Elongation is the process of RNA polymerase moving along the DNA template strand, synthesizing a complementary RNA strand. Termination occurs when RNA polymerase reaches the terminator sequence and detaches from the DNA.

During transcription, the DNA template strand is read by RNA polymerase in the 3' to 5' direction. The RNA strand is synthesized in the 5' to 3' direction.

RNA processing refers to the modifications made to the primary RNA transcript (pre-mRNA) before it is transported out of the nucleus in eukaryotic cells. These modifications include 5' capping, splicing, and polyadenylation.

Exons are the coding regions of a gene that are transcribed into mRNA and eventually expressed as protein. Exons are spliced together after the removal of non-coding regions called introns during RNA processing in eukaryotes.

A 7-methylguanosine cap is added to the 5' end of the mRNA, protecting the mRNA from degradation, helping with ribosome binding during translation, and facilitating mRNA export from the nucleus.

Non-coding regions called introns are removed, and the remaining exons are joined together to form a continuous coding sequence.

A poly-A tail is added to the 3' end of the mRNA, which aids in stability, transport, and translation initiation.

RNA processing is necessary in eukaryotes because they have introns in their genes, and mRNA must be properly modified before it can be translated into a protein. Prokaryotes do not have introns and typically do not require such extensive RNA processing.

Non-coding regions of DNA that are transcribed into RNA but are not used to make proteins. They are removed from pre-mRNA during RNA splicing.

A modified guanine nucleotide added to the 5' end of mRNA. It protects mRNA from degradation, helps with mRNA stability, and aids in ribosome binding.

A string of adenine nucleotides added to the 3' end of mRNA. It helps stabilize mRNA, aids in nuclear export, and plays a role in translation initiation.

The building blocks of proteins. Each one consists of a central carbon atom, hydrogen, a carboxyl group, an amino group, and a variable side chain.

A covalent bond between the carboxyl group of one amino acid and the amino group of another. It links amino acids together into a polypeptide chain.

Codons that code for specific amino acids.

Codons that do not code for any amino acid and instead signal the termination of translation.

There are 64 possible codons because there are four nucleotide bases (A, U, C, G) and codons are three bases long (4³ = 64).

The redundancy of the genetic code where multiple codons code for the same amino acid. The third base of a codon can often vary without changing the amino acid it codes for.

They are UAA, UAG, and UGA. These codons signal the end of translation, causing the ribosome to detach from the mRNA and release the synthesized polypeptide chain.

AUG is the first codon of mRNA that is recognized by the ribosome to begin translation. It codes for the amino acid methionine in eukaryotes.

It maps each of the 64 codons to the corresponding amino acid. For example, AUG codes for methionine, UUU codes for phenylalanine, and UAA, UAG, and UGA are stop codons.

A mutation that changes a codon for one amino acid into a codon for a different amino acid.

A mutation that changes a codon for an amino acid into a stop codon, causing the protein to be prematurely terminated.

A mutation that inserts or deletes nucleotides in a number that is not a multiple of three, shifting the reading frame of the codons, resulting in a completely incorrect sequence of amino acids.

Mutations are the source of genetic variation, which is essential for evolution. Beneficial mutations can give an organism an advantage in its environment.

The study of genes, inheritance, and genetic variation in organisms.

A structure made of DNA and proteins that contains many genes. Organisms have a specific number of chromosomes in their cells.

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

The study of an organism's genome, including the sequencing, analysis, and comparison of its complete DNA sequence.

DNA serves as genetic information by encoding the instructions that are necessary for the development, functioning, and reproduction of living organisms.

Protein synthesis is a two-step process that involves transcription and translation.

A cluster of functionally related genes found in prokaryotic cells. An operon consists of a promoter, an operator, and structural genes.

Proteins that bind to the operator region of an operon, blocking RNA polymerase from transcribing the genes.

Molecules that bind to repressor proteins and inactivate them, allowing RNA polymerase to transcribe the operon.

Proteins that enhance the binding of RNA polymerase to the promoter, increasing transcription.

In E. coli, the presence of glucose inhibits the transcription of genes involved in the metabolism of other sugars, such as lactose.

The process of removing introns and joining exons to produce a mature mRNA molecule.

Different combinations of exons can be spliced together, leading to multiple protein variants from a single gene.

The stability of the mRNA molecule can be regulated, influencing how long it remains in the cell before being degraded.

Small RNA molecules (like miRNA and siRNA) can bind to mRNA molecules, leading to their degradation or preventing translation.

One nucleotide is replaced by another (e.g., A → G).

A section of DNA is removed from the sequence.

Large molecular machines composed of rRNA and proteins, found in the cytoplasm of both prokaryotes and eukaryotes. Their main function is to translate the genetic code carried by messenger RNA (mRNA) into a polypeptide chain.

Ribosomes consist of two subunits: the large subunit and the small subunit. The large subunit is responsible for forming peptide bonds between amino acids, while the small subunit binds to the mRNA and reads its codons.

A sequence of three nucleotides found on tRNA molecules. The anticodon is complementary to the codon on the mRNA, ensuring that the correct amino acid is delivered for protein synthesis.

During translation, the ribosome reads the mRNA template from the 5' end towards the 3' end. Each codon, consisting of three nucleotides, is read sequentially and matched with the corresponding tRNA molecule.

Three crucial sites on a ribosome where tRNA molecules interact during translation: (1) A site (Aminoacyl site): where a tRNA carrying an amino acid binds to the mRNA codon; (2) P site (Peptidyl site): where the tRNA carrying the growing polypeptide chain is located; (3) E site (Exit site): where the empty tRNA exits the ribosome after delivering its amino acid.

1. Initiation: The small ribosomal subunit binds to the mRNA at the start codon (AUG), followed by the initiator tRNA (carrying methionine) binding to the start codon in the P site. The large subunit then binds to the small subunit, forming the functional ribosome. 2. Elongation: A tRNA carrying the next amino acid enters the A site, a peptide bond forms between the amino acid in the A site and the growing polypeptide chain in the P site. The ribosome translocates, shifting the mRNA and tRNA, causing the tRNA in the P site to move to the E site and exit, while the tRNA in the A site moves to the P site. This cycle repeats. 3. Termination: The ribosome reaches a stop codon (UAA, UAG, or UGA) and a release factor binds to it , causing the ribosome to release the newly synthesized polypeptide chain. The ribosomal subunits dissociate from the mRNA.

In prokaryotes, transcription (making mRNA from DNA) and translation (making protein from mRNA) occur simultaneously in the cytoplasm. There is no nuclear membrane to separate these processes, allowing for efficient protein synthesis.

A permanent change in the DNA sequence of an organism's genome. Mutations can lead to changes in the structure and function of proteins.

Physical or chemical agents that increase the rate of mutation. Examples include radiation (X-rays, UV light) and chemicals (such as those in tobacco smoke).

Mutations that occur naturally without external influences. These mutations result from errors during DNA replication or spontaneous chemical changes in the DNA.

Base substitutions (or point mutations) involve replacing one nucleotide with another in the DNA sequence. This can lead to changes in the amino acid sequence of a protein.

This mutation involves the insertion of one or more extra nucleotides into the DNA sequence. Insertions can shift the reading frame of the genetic code, leading to a completely different protein.

This mutation involves the removal of one or more nucleotides from the DNA sequence. Deletions can also shift the reading frame of the genetic code, leading to a different protein.

Frame-shift mutations are caused by insertions or deletions of nucleotides that are not a multiple of three. These mutations can change the reading frame of the DNA, leading to a completely different protein.

These mutations occur when a single nucleotide is replaced with another nucleotide. Silent mutations occur when the change in the DNA sequence does not change the amino acid sequence of the protein.