ASCP Molecular Biology Exam Prep

Questions and Answers

What is a pyrimidine?

Two carbon rings

Contains Adenine and Guanine

One carbon ring (correct)

Contains Cytosine, Thymine, Uracil (correct)

What is a purine?

Contains Uracil

Contains Adenine and Guanine (correct)

Two carbon rings (correct)

One carbon ring

How are nucleotides joined together?

Condensation

What does mRNA do?

Carries code out of the cell for protein structure from DNA to ribosomes. Signup and view all the answers

What does tRNA do?

Decodes mRNA and matches amino acids to mRNA code for protein synthesis. Signup and view all the answers

What does rRNA do?

Part of ribosome structure that coordinates coupling of tRNA to mRNA codons. Signup and view all the answers

What is feedback inhibition?

The end product of a pathway acts as a noncompetitive inhibitor by binding to the allosteric site to slow down the reaction. Signup and view all the answers

What are exonucleases?

Enzymes that degrade nucleic acids by removing one terminal nucleotide at a time. Signup and view all the answers

What are endonucleases?

Enzymes that cleave phosphodiester bonds within the chain. Signup and view all the answers

What is DNA polymerase III?

Enzyme that copies DNA by reading existing strands and building new complementary strands. Signup and view all the answers

What are ORI sites?

Origin of replication on the chromosome that triggers DNA replication. Signup and view all the answers

What is the function of helicase?

Breaks hydrogen bonds of the double helix. Signup and view all the answers

What does ligase do?

Closes gaps in DNA and forms covalent bonds between nucleotides. Signup and view all the answers

What are telomeres?

Caps at the ends of chromosomes that preserve DNA during replication. Signup and view all the answers

What is the role of RNA polymerase?

Opens double helix and reads one strand to make RNA in an antiparallel direction. Signup and view all the answers

What do spliceosomes do?

Remove introns during transcription and reform bonds between exons. Signup and view all the answers

What is the function of enhancers?

Maintain tissue-specific or cell-specific levels of gene expression. Signup and view all the answers

What is a Poly-A tail?

A sequence added to the 3' end of mRNA that keeps it from being destroyed. Signup and view all the answers

What is the purpose of the 5' cap?

Added to the 5' end of finished mRNA to signal readiness for translation. Signup and view all the answers

What is aminoacyl tRNA?

tRNAs that carry amino acids. Signup and view all the answers

What is the function of ribosomes?

Where mRNAs and tRNAs meet and catalyze peptide bond formation. Signup and view all the answers

What is the path of a tRNA in a ribosome?

From A site to P site to E site. Signup and view all the answers

How is translation initiated?

Small subunit binds to ribosomal binding site and MET anticodon binds to the start codon. Signup and view all the answers

How is translation terminated?

A stop codon is recognized by a release factor, breaking the bond between the chain and tRNA. Signup and view all the answers

What is reverse transcriptase?

An enzyme that allows RNA to be converted to DNA. Signup and view all the answers

What is pleiotropy?

A single gene influences multiple phenotypic traits. Signup and view all the answers

Study Notes

Nucleotides and Nitrogenous Bases

Pyrimidines consist of a single carbon ring and include Cytosine, Thymine, and Uracil.
Purines are characterized by two carbon rings and include Adenine and Guanine.
Nucleotides are joined together through condensation reactions.

RNA Function and Types

mRNA (messenger RNA) carries genetic code from DNA to ribosomes for protein synthesis; marks the transition from transcription to translation.
tRNA (transfer RNA) decodes mRNA and matches amino acids to the corresponding mRNA code, crucial for protein synthesis.
rRNA (ribosomal RNA) forms part of the ribosome's structure, is the most abundant RNA, and facilitates the coupling of tRNA to mRNA codons.

Enzymes and Inhibition

Feedback Inhibition occurs when the end product of a metabolic pathway acts as a noncompetitive inhibitor, binding to an allosteric site.
Exonucleases degrade nucleic acids by removing nucleotides one at a time from the ends by cleaving phosphodiester bonds.
Endonucleases cleave phosphodiester bonds within a nucleic acid chain, often at palindromic recognition sites and creating sticky ends.

DNA Replication Mechanism

DNA polymerase III synthesizes new DNA strands by reading existing ones and always adds nucleotides to the 3' end; it cannot initiate a strand independently.
ORI (origin of replication) sites trigger the replication process on chromosomes.
Gyrase (a type of topoisomerase) unwinds DNA ahead of the replication fork to relieve tension.
Helicase breaks hydrogen bonds in the double helix to separate strands for replication.
Primase synthesizes RNA primers, providing starting points for DNA polymerase III.

Strands and Fragments

Single-strand DNA-binding proteins (SSBPs) stabilize unwound DNA during replication.
Okazaki fragments are short DNA segments synthesized on the lagging strand, later joined by DNA ligase.
DNA ligase forms covalent bonds between nucleotides, sealing gaps during replication.

Processes in DNA Replication

Steps of DNA replication include initiation, elongation, and termination.
Telomeres protect the ends of chromosomes during replication to maintain genetic integrity.

Transcription Elements

The -10 box (TATA box) is a promoter region located 10 bases upstream of the transcription start site, facilitating RNA polymerase binding.
The -35 box, TTGACA, is another promoter element located 35 bases upstream of the start site.

RNA Polymerase Activity

RNA polymerase opens the DNA double helix and synthesizes RNA in the 3' to 5' direction, forming covalent bonds between nucleotides.

Post-Transcriptional Modifications

Spliceosomes, comprised of small nuclear RNAs (snRNPs), remove introns and join exons during RNA processing.
Enhancers are regulatory elements located far from promoters that influence tissue-specific or cell-specific gene expression.
The Poly-A tail, a series of 100-250 adenine nucleotides, protects mRNA from degradation in the cytoplasm.
The 5' cap is added to the mRNA's 5' end, signaling readiness for translation and providing a binding site for ribosomes.

Translation Mechanics

Aminoacyl tRNA refers to tRNAs that carry specific amino acids.
Ribosomes consist of large and small subunits that facilitate the interaction between mRNA and tRNAs, catalyzing peptide bond formation.
The tRNA moves through the ribosome in the order A (aminoacyl site) → P (peptidyl site) → E (exit site).

Initiation and Termination of Translation

Translation initiation occurs when the small ribosomal subunit binds to the mRNA's ribosomal binding site, followed by the large subunit joining the complex.
Termination happens when a stop codon is encountered, with a release factor binding to the ribosome, leading to the release of the newly synthesized polypeptide.

Reverse Transcription

Reverse transcriptase is an enzyme that converts RNA into DNA, following the path mRNA → ssDNA → cDNA → dsDNA.

Genetic Concepts

Pleiotropy refers to the phenomenon where a single gene influences multiple phenotypic traits.

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Prepare for the ASCP Molecular Biology Exam with this comprehensive quiz focusing on key concepts such as nucleotides and their functions. Each flashcard includes definitions and detailed explanations to enhance your understanding of molecular biology. Perfect for students and professionals alike!