Principles of Biology I - Lecture Exam 4 Review

Comprehensive vocabulary flashcards covering transcription, translation, mutations, operons, and cancer genetics based on the BIOL 150 Exam 4 review.

RNA Polymerase

An enzyme that builds RNA in the $5' \rightarrow 3'$ direction by adding new bases to the $3'$ end while reading the DNA template strand in the $3' \rightarrow 5'$ direction.

Promoter

A DNA 'landing site' located just upstream of a gene where RNA polymerase binds with the help of transcription factors to initiate transcription.

Template (antisense) strand

The specific DNA strand that is actually read by RNA polymerase during the transcription process.

Coding (sense) strand

The DNA strand that has the same sequence as the resulting mRNA (with $T$ instead of $U$) and is the antiparallel partner to the template strand.

5' cap

A modification added to the front of eukaryotic pre-mRNA that protects the mRNA and assists in its exit from the nucleus.

Poly-A tail

A modification added to the $3'$ end of eukaryotic pre-mRNA that provides protection and helps the message leave the nucleus.

Introns

Non-coding segments of pre-mRNA that are removed by the spliceosome and are not present in the mature mRNA.

Exons

The coding regions of pre-mRNA that are kept and joined together to form the mature mRNA used for translation.

Spliceosome

A complex made of protein and snRNA responsible for splicing out introns and joining exons together.

Alternative Splicing

A process where different combinations of exons from the same pre-mRNA are joined, allowing one gene to code for several different proteins.

Reverse Transcriptase

An enzyme used by retroviruses like HIV to copy an RNA genome back into DNA ($RNA \rightarrow DNA$).

Codon

A unit of $3$ nucleotides in mRNA that is read non-overlappingly to specify one amino acid or a start/stop signal.

Degenerate code

A property of the genetic code where several different codons can specify the same amino acid, which allows for silent mutations.

AUG

The specific mRNA start codon that sets the reading frame and codes for the amino acid Methionine ($Met$).

Stop Codons

The mRNA sequences $UAA$, $UAG$, and $UGA$, which do not code for amino acids and signal the end of translation.

tRNA

The RNA molecule that carries amino acids to the ribosome and matches them to mRNA codons using its anticodon.

Anticodon

A three-nucleotide sequence on tRNA that pairs with a complementary mRNA codon in an antiparallel orientation.

A site (Amino acid)

The ribosomal site where a new aminoacyl-tRNA enters to begin its addition to the growing protein chain.

P site (Peptide)

The ribosomal site that holds the growing polypeptide chain and where the first Methionine tRNA settles during initiation.

E site (Exit)

The ribosomal site where an empty tRNA leaves the ribosome after its amino acid has been added to the chain.

Release factor

A protein that binds to a stop codon in the A site, causing the finished polypeptide to be released and the ribosome to disassemble.

Silent Mutation

A point mutation where a base change occurs but the same amino acid is produced due to the redundancy of the genetic code.

Missense Mutation

A point mutation where a single base change results in one amino acid being replaced by a different amino acid.

Nonsense Mutation

A point mutation that changes an amino acid codon into a premature stop codon, resulting in a truncated protein.

Frameshift Mutation

A mutation caused by the insertion or deletion of nucleotides (not in multiples of $3$) that shifts the reading frame for all downstream codons.

Operator

A DNA segment that acts as a 'switch' within an operon where a repressor protein can bind to block RNA polymerase.

Inducible Operon (lac)

An operon that is normally OFF but can be turned ON by a signal (like lactose) that inactivates the repressor.

Repressible Operon (trp)

An operon that is normally ON but can be turned OFF by a signal (like tryptophan) that activates the repressor.

Proto-oncogene

A gene that normally promotes cell growth and division; mutations can turn it into a dominant, overactive oncogene.

Ras

A proto-oncogene that acts as a molecular switch; cancer mutations lock it in the active GTP-bound state, signaling the cell to divide constantly.

p53

A tumor suppressor known as the 'guardian of the genome' that stops the cell cycle for DNA repair or triggers apoptosis if damage is too severe.