Chapter 8 c): Gene Expression and Protein Synthesis

These flashcards cover key concepts related to gene expression, transcription, translation, and the genetic code based on the lecture notes.

What was the key experiment by Beadle and Tatum in 1941?

It demonstrated that genetic mutations in the mold Neurospora crassa could affect gene expression and enzymes, leading to the "one gene-one enzyme" hypothesis.

What is the Central Dogma of Molecular Biology?

It describes the flow of genetic information: DNA is transcribed into RNA, which is then translated into protein.

Where does transcription occur in eukaryotic cells?

Transcription occurs in the nucleus, while translation occurs in the cytoplasm.

What are the components of a gene?

A gene comprises a promoter (initiation site), regulatory sequences (enhancers/silencers), a transcribed region (the template), and a terminator (stop signal).

What is the function of transcription factors (TFs)?

TFs are proteins that bind to specific DNA sequences to recruit RNA polymerase to a promoter region, thereby initiating transcription.

What are the three stages of transcription?

Initiation: RNA polymerase binds the promoter with the help of transcription factors.\n2. Elongation: RNA polymerase synthesizes RNA in the 5' \rightarrow 3' direction.\n3. Termination: The polymerase reaches a terminator sequence and releases the RNA transcript.

What is the TATA box?

A conserved DNA sequence within the promoter region of eukaryotes that helps position RNA polymerase II for transcription initiation.

What is RNA splicing?

A post-transcriptional modification process where non-coding introns are removed and coding exons are joined together in a pre-mRNA molecule.

What is the significance of alternative splicing?

It allows a single gene to encode multiple unique protein isoforms by selectively including or excluding specific exons during mRNA processing.

What is the function of the 5' cap and the 3' poly-A tail?

• 5'Cap: A modified guanine that prevents degradation and assists in ribosome binding.

• 3' Poly-A Tail: A sequence of adenine nucleotides that increases mRNA stability and facilitates nuclear export.

How does RNA differ structurally from DNA?

RNA contains the sugar ribose (instead of deoxyribose), is typically single-stranded, and uses uracil (U) instead of thymine (T).

What is the genetic code?

The set of rules using three-nucleotide triplets (codons) to specify the particular amino acids that will be added to a polypeptide chain.

What is the role of tRNA and anticodons?

Transfer RNA (tRNA) carries specific amino acids to the ribosome; its anticodon pairs with a complementary mRNA codon to ensure correct sequencing.

How does aminoacyl-tRNA synthetase function?

This enzyme catalyzes the attachment of a specific amino acid to its corresponding tRNA, a process known as "charging."

Describe the three tRNA binding sites in a ribosome (A, P, and E).

• A site (Aminoacyl): Accepts incoming charged tRNAs.\n- P site (Peptidyl): Holds the tRNA attached to the growing polypeptide chain.\n- E site (Exit): Where the uncharged tRNA exits the ribosome.

What is the role of rRNA in ribosomes?

Ribosomal RNA (rRNA) provides structural integrity and acts as a ribozyme to catalyze peptide bond formation between amino acids.

What happens during translation termination?

Translation ends when a stop codon reaches the A-site; a release factor binds, causing the polypeptide to be released and the ribosome subunits to disassemble.

What is a point mutation?

A genetic alteration involving the change of a single nucleotide. Types include silent, missense, and nonsense mutations.

Differentiate between missense and nonsense mutations.

• Missense: A single nucleotide change results in a different amino acid.\n- Nonsense: A mutation changes a sense codon into a premature stop codon, leading to a truncated protein.

What is a frameshift mutation?

An insertion or deletion of nucleotides (not in a multiple of three) that shifts the reading frame, altering every amino acid downstream of the mutation.