Cell Biology and Genetics: Transcription and Translation

Flashcards covering key concepts of nucleic acid structure, gene expression, transcription, and translation based on lecture notes.

What two-step process is required to produce proteins from genes on DNA according to the Central Dogma of Biology?

Transcription (producing mRNA from DNA) and Translation (translating mRNA into protein structure).

Why must mRNA be produced in the nucleus during protein synthesis?

Because DNA cannot leave the cell nucleus, while protein synthesis occurs outside the nucleus in the cytoplasm. Messenger RNA (mRNA) acts as a messenger carrying genetic information outside the nucleus.

What chemical elements compose nucleic acids, and what is their primary function at the molecular level?

Nucleic acids are composed of $\text{C}$, $\text{H}$, $\text{O}$, $\text{N}$, and $\text{P}$. Their primary function is to store and process information at the molecular level.

According to the structural diagram of a nucleotide, what three major components form its structure?

A phosphate group, a sugar (ribose or deoxyribose), and a nitrogenous base (purine or pyrimidine).

Which nitrogenous bases and sugars are specific to DNA and RNA?

Thymine (T) and deoxyribose sugar are specific to DNA, while Uracil (U) and ribose sugar are specific to RNA. Adenine (A), Guanine (G), and Cytosine (C) are found in both.

Which nitrogenous bases belong to the purines category, and what is their ring structure?

Adenine (A) and Guanine (G) are purines, which are double-ringed molecules.

Which nitrogenous bases belong to the pyrimidines category, and what is their ring structure?

Cytosine (C), Thymine (T) (DNA only), and Uracil (U) (RNA only) are pyrimidines, which are single-ringed molecules.

What base-pairing rules govern the double-stranded structure of DNA?

Hydrogen bonds form strictly between purines and pyrimidines: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

What are the three main types of RNA and their specific functions?

1. Messenger RNA (mRNA): Transcribed from DNA to become the information needed to make proteins. 2. Transfer RNA (tRNA): Carries amino acids during translation. 3. Ribosomal RNA (rRNA): Involved in protein synthesis.

What events occur during gene activation prior to transcription?

DNA is temporarily uncoiled, histones are removed to make genes accessible, and hydrogen bonds between complementary DNA bases are temporarily broken.

How does RNA polymerase synthesize mRNA during transcription?

RNA polymerase binds to the start signal in the promoter region of a gene, reads the DNA template strand, forms complementary hydrogen bonds with free nucleotides, and joins nucleotides using covalent bonds until reaching a termination sequence.

Identify the binding sites and subunits shown in the structural diagram of a ribosome.

The ribosome consists of a $50\text{S}$ subunit containing the E (exit) site, P (peptidyl) site, and A (aminoacyl) site; a $30\text{S}$ subunit; and an mRNA-binding site.

According to the structural diagram of a transfer RNA (tRNA) molecule, what key structural regions are labeled?

The $3'$ amino acid-accepting end, Loop 1, Loop 2 containing the anticodon, and Loop 3.

According to Table 3-1 Examples of the Genetic Code, what mRNA codon, tRNA anticodon, and amino acid correspond to the DNA template triplet TAC?

The DNA template triplet TAC corresponds to the mRNA codon AUG, the tRNA anticodon UAC, and the amino acid Methionine.

What steps occur during the initiation phase of translation?

Step 1: mRNA binds to the small ribosomal subunit near the P site, and tRNA carrying the first amino acid binds to the mRNA start codon. Step 2: The large ribosomal subunit binds and interlocks around mRNA, and a second tRNA binds to the A site.

How are amino acids joined into a growing polypeptide chain during translation elongation?

Ribosomal enzymes remove the amino acid from tRNA in the P site and attach it via a peptide bond to the amino acid on tRNA in the A site. The ribosome moves one codon down mRNA, releasing the empty tRNA from the E site.

What process occurs during translation termination when a stop codon is reached?

A ribosomal enzyme breaks the bond between the polypeptide and tRNA in the P site, releasing the polypeptide chain. The ribosomal subunits then break apart and release the mRNA strand.