DNA Structure and Composition

Flashcards based on lecture notes about DNA structure and composition for BMSC D604 Molecular Foundations of Medicine.

What is the central dogma of molecular biology?

The flow of information from DNA to RNA to protein.

What is an exception to the central dogma of molecular biology?

Retroviruses, which use reverse transcriptase to convert RNA to DNA.

Where is genetic information stored in eukaryotes?

Nucleus and mitochondria.

What is the structure of prokaryotic DNA?

One molecule of circular dsDNA exhibiting supercoiling, and plasmids.

What is the structure of eukaryotic chromosomal DNA?

Linear strand of dsDNA associated with proteins to form chromatin.

How is mitochondrial DNA (mtDNA) inherited?

Maternally.

What does mtDNA encode?

2 rRNAs, 22 tRNAs, and 13 oxidative phosphorylation proteins.

What are nucleosomes?

DNA bound to histones.

What is the charge of histones at physiological pH?

Positive.

What two amino acids are histones rich in?

Lysine and arginine.

What are the building blocks of DNA?

Deoxyadenylate, deoxyguanylate, deoxythymidylate, and deoxycytidylate.

What is the primary structure of DNA?

Base sequence (linear polymer of dNMPs).

What kind of bonds link DNA?

3' to 5' phosphodiester bonds.

Which groups are connected by phosphodiester bonds?

3'-OH group on one deoxyribose and 5'-PO4 on another deoxyribose.

What are the base pairings in DNA?

A pairs with T, and G pairs with C (Purine with Pyrimidine).

What is Chargaff's Rule?

Amount of purine = amount of pyrimidine.

In what direction is a DNA sequence written/read?

5' to 3' direction.

What is the secondary structure of DNA?

Double helix with anti-parallel strands.

Describe the orientation of the base pairs and phosphate backbone in the DNA double helix.

Bases point inward, phosphate backbone faces outward.

What are the three structural forms of the DNA helix?

A, B, and Z forms.

What are intercalating agents?

Compounds that can be positioned between base pairs and cause mutations or DNA breakage (e.g., Actinomycin D, doxorubicin, ethidium bromide).

What enzyme do retroviruses use to convert their RNA into DNA?

Reverse transcriptase (RNA-dependent DNA polymerase)

How does AZT work in HIV treatment?

It is incorporated by viral reverse transcriptase as a chain terminator to stop DNA elongation.

What is the function of topoisomerases?

Topoisomerases introduce transient breaks into DNA to relieve supercoiling during replication and transcription.

How does type I topoisomerase work?

Type I topoisomerase cuts one strand of the DNA helix, relaxes the supercoil, and then reseals the strand (no ATP required).

How does type II topoisomerase work?

Type II topoisomerase cuts both strands of the DNA helix, relaxes the supercoil, and then reseals the strands (ATP required).

What is the function of DNA polymerase?

DNA polymerase is an enzyme that synthesizes new DNA strands using an existing strand as a template.

In what direction does DNA polymerase synthesize DNA?

DNA polymerase synthesizes DNA in the 5' to 3' direction, adding nucleotides to the 3' -OH end of the growing strand.

What are the key components required for DNA replication?

Template DNA, primers, DNA polymerase, and dNTPs (deoxyribonucleotide triphosphates).

What is the role of DNA ligase?

DNA ligase joins Okazaki fragments on the lagging strand during DNA replication by catalyzing the formation of phosphodiester bonds.

What are telomeres and their function?

Telomeres are repetitive nucleotide sequences at the ends of chromosomes that protect DNA from degradation and maintain genomic stability.

Which enzyme maintains telomeres, and how does it work?

Telomerase is a reverse transcriptase that adds repetitive sequences to the 3' end of telomeres, compensating for shortening during replication.

What is the role of telomerase in cancer?

Telomerase is often reactivated in cancer cells, allowing them to maintain telomere length and bypass cellular senescence, promoting uncontrolled proliferation.

What are the three main types of RNA?

Messenger RNA (mRNA), Transfer RNA (tRNA), and Ribosomal RNA (rRNA).

What is the function of mRNA?

mRNA carries genetic information from DNA in the nucleus to the ribosomes in the cytoplasm for protein synthesis.

What is the function of tRNA?

tRNA brings amino acids to the ribosome for protein synthesis, matching the mRNA codon with its anticodon.

What is the function of rRNA?

rRNA forms the structural and catalytic core of ribosomes, facilitating protein synthesis.

What is transcription?

Transcription is the process of synthesizing RNA from a DNA template.

What is translation?

Translation is the process of synthesizing a protein from an mRNA template.

What is a gene?

A gene is a sequence of DNA that encodes a functional RNA or protein product.

What is a promoter?

A promoter is a region of DNA where RNA polymerase binds to initiate transcription.

What is an operon?

An operon is a cluster of genes under the control of a single promoter, common in prokaryotes.

What is a codon?

A codon is a three-nucleotide sequence in mRNA that specifies a particular amino acid or stop signal during translation.

What is an anticodon?

An anticodon is a three-nucleotide sequence in tRNA that is complementary to an mRNA codon.

What is RNA polymerase?

RNA polymerase is an enzyme that synthesizes RNA from a DNA template during transcription.

What is a ribosome?

A ribosome is a complex of rRNA and proteins that synthesizes proteins during translation.

What is a start codon?

Start codons initiate protein synthesis (typically AUG, encoding methionine).

What is a stop codon?

Stop codons terminate protein synthesis (UAA, UAG, UGA).

What is splicing?

Splicing is the process of removing introns and joining exons in pre-mRNA to form mature mRNA.

What are introns?

Introns are non-coding regions of a gene that are removed during splicing.

What are exons?

Exons are coding regions of a gene that are joined together during splicing to form mature mRNA.

What is alternative splicing?

Alternative splicing is a process by which different combinations of exons are joined together to produce multiple mRNA isoforms from a single gene.

What is the 5' cap?

The 5' cap is a modified guanine nucleotide added to the 5' end of pre-mRNA to protect it from degradation and enhance translation.

What is the poly-A tail?

The poly-A tail is a sequence of adenine nucleotides added to the 3' end of pre-mRNA to protect it from degradation and enhance translation.

What is a mutation?

A mutation is a change in the nucleotide sequence of DNA.