Cell Biology: Transcription and Gene Expression

The process of copying genetic information from DNA to RNA. It involves the synthesis of a messenger RNA (mRNA) molecule that carries the code for protein synthesis.

The process of converting the genetic code carried by mRNA into a protein. It involves the ribosome reading the mRNA sequence and assembling amino acids into a polypeptide chain.

DNA replication is a process of copying the entire DNA molecule before cell division. Protein synthesis is the process of producing a specific protein based on the genetic code carried by mRNA. Replication occurs before cell division, while protein synthesis happens continuously for various cellular functions.

Eukaryotic chromosomes are linear and organized into nucleosomes, which are DNA wrapped around histone proteins. This structure helps compact and regulate genetic material.

Bacterial chromosomes are circular and lack histones. The DNA is supercoiled to fit within the small bacterial cell.

Transcription in eukaryotes occurs inside the nucleus, where the DNA resides.

Transcription in bacteria happens in the cytoplasm, where the DNA is located.

The eukaryotic promoter contains a TATA box (a conserved DNA sequence) and other regulatory elements that control gene expression.

Segments of DNA that code for proteins. They can be spliced out or kept in a mRNA transcript.

A sequence of nucleotides on mRNA that binds to ribosomes during translation, initiating protein synthesis. It does not participate in transcription.

The strand of DNA that has the same sequence as the mRNA (except with T's instead of U's). It's not directly used in transcription, but helps visualize the mRNA sequence.

A string of adenine nucleotides added to the 3' end of mRNA after transcription in eukaryotes. It functions in mRNA stability and translation.

A point mutation in a DNA sequence that does not lead to a change in the amino acid sequence of the protein. This can happen when the mutation occurs in a non-coding region or when the altered codon codes for the same amino acid.

A point mutation that changes a single nucleotide in a DNA sequence, resulting in a different amino acid being incorporated into the protein.

A point mutation that changes a codon for an amino acid into a stop codon, prematurely terminating protein synthesis.

The first codon in a messenger RNA (mRNA) sequence that signals the start of protein synthesis by initiating the translation process.

A codon in a messenger RNA (mRNA) sequence that signals the termination of protein synthesis, ending the translation process.

A mistake during the process of copying DNA, potentially causing an alteration in the DNA sequence. These errors can be corrected by enzymes, but some may persist as mutations.

A permanent change in the DNA sequence of an organism. Mutations can arise spontaneously or be induced by environmental factors.

Eukaryotic genes contain introns, non-coding sequences that need to be removed before translation. Splicing is the process that removes these introns, resulting in a mature mRNA molecule ready for translation.

Transcription initiation in bacteria starts at the promoter region, which is located at -35 and -10 nucleotides upstream of the gene's starting point. This region contains specific sequences recognized by the sigma factor of RNA polymerase, allowing transcription to begin.

In eukaryotes, transcription initiation starts at the TATA box, a conserved sequence located about 30 nucleotides upstream of the gene's starting point. This sequence is recognized by the TATA-binding protein (TBP), which recruits other transcription factors to initiate transcription.

A 5' cap is a modified guanine nucleotide added to the 5' end of eukaryotic mRNA. This modification protects the mRNA from degradation and helps with ribosome binding during translation.

A 3' poly A tail is a string of adenine nucleotides added to the 3' end of eukaryotic mRNA. It protects the mRNA from degradation and aids in its export from the nucleus.

The interaction between proteins and DNA is crucial for various cellular processes, particularly gene regulation. This binding is usually based on non-covalent interactions, including hydrogen bonds and hydrophobic interactions.

In bacteria, translation initiation begins with the ribosome binding to the Shine-Dalgarno sequence, which is located upstream of the start codon AUG. This sequence is recognized by the small subunit of bacterial ribosomes.

In eukaryotes, translation initiation occurs when the ribosome binds directly to the 5' cap of the mRNA. From there, it scans the mRNA until it encounters the start codon AUG, initiating protein synthesis.

The wobble hypothesis explains how a single tRNA can recognize multiple codons that differ only in their third base. This is because the third base of the anticodon can pair with more than one base in the mRNA codon.

A reading frame refers to the specific grouping of nucleotides (codons) into triplets that are read during translation. Each possible reading frame results in a different amino acid sequence.

The template strand of DNA is used as a template for mRNA synthesis during transcription. It is the non-coding strand and runs 3' to 5'.

Aminoacyl-tRNA synthetases are enzymes responsible for attaching the correct amino acid to its corresponding tRNA molecule. This process is crucial for accurate translation.

A frameshift mutation is an insertion or deletion of nucleotides in a DNA sequence that shifts the reading frame, leading to a completely different amino acid sequence.

The lac operon is a group of genes that are regulated by the presence of lactose. When lactose is present, the lac operon is induced, meaning that the genes are transcribed and translated. This allows the cell to produce the enzymes needed to metabolize lactose.

LacI is a protein that binds to the operator region of the lac operon. When LacI is bound to the operator, it prevents RNA polymerase from transcribing the genes in the operon. This keeps the lac operon off when lactose is absent.

When lactose is present, it binds to LacI, causing a conformational change in LacI. This change makes LacI unable to bind to the operator, allowing RNA polymerase to transcribe the lac operon.

The maltose operon is an example of positive regulation. This means that a protein is required to activate the expression of the genes in the operon. Maltose acts as an inducer, activating transcription.

MalT is a protein that binds to maltose. When maltose binds to MalT, it changes the conformation of MalT, allowing it to bind to the promoter of the maltose operon.

The malPQ genes encode for proteins involved in the transport and metabolism of maltose. The expression of these genes is regulated by the maltose operon.