Biological Macromolecules: Structure, Function, and DNA Replication

What are carbohydrates primarily composed of?

Carbon, hydrogen, and oxygen.

What are monosaccharides?

Single-sugar units such as glucose, fructose, and galactose that serve as immediate energy sources.

What is a disaccharide?

A carbohydrate formed by two monosaccharides joined together, such as lactose.

What are polysaccharides?

Long chains of monosaccharides, examples include glycogen and cellulose.

What is the primary function of triglycerides?

They serve as the body's primary long-term energy storage in adipose tissue.

What are phospholipids?

Amphipathic molecules that form the phospholipid bilayer of cell membranes.

What role do steroids play in biology?

They include hormones such as cortisol, testosterone, estrogen, and progesterone.

What are proteins made of?

Amino acids, which are the monomers of proteins.

What is the function of proteins in cells?

They act as molecular machines, catalyzing reactions, transporting molecules, and providing structure.

What is a nucleotide composed of?

A pentose sugar, a phosphate group, and a nitrogenous base.

What is the function of nucleic acids?

They store and convey genetic information.

What must a hereditary molecule be able to do?

Replicate, store information, express information, and allow mutations.

Who proposed the concept of genes as units of heredity?

Wilhelm Johannsen in 1909.

What did Griffith's experiment with Streptococcus demonstrate?

A 'transforming principle' transfers pathogenicity from heat-killed S strain to live R strain.

What did Avery, MacLeod, and McCarty conclude about the transforming principle?

DNA is the hereditary material because DNase prevented transformation.

What did Chargaff's rules state?

In DNA, the proportion of adenine equals thymine and the proportion of cytosine equals guanine.

What did the Hershey-Chase experiment demonstrate?

DNA carries genetic instructions as only DNA entered bacteria during phage infection.

What did Rosalind Franklin and Maurice Wilkins contribute to DNA research?

They used X-ray diffraction to reveal DNA's helical structure.

What is the significance of the sugar-phosphate backbone in DNA?

It provides stability and protection for the genetic material.

What are the two types of nitrogenous bases in nucleotides?

Purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil).

What is the orientation of the two strands in a DNA double helix?

They run antiparallel, one oriented 5'→3' and the other 3'→5'.

How do complementary base pairs in DNA bond?

A pairs with T via two hydrogen bonds, and C pairs with G via three hydrogen bonds.

What is the overall charge of DNA due to its phosphate groups?

DNA has an overall negative charge.

What is the role of major and minor grooves in DNA?

They create recognition surfaces for proteins involved in regulation and replication.

What is the structure of B-DNA?

A right-handed helix with alternating major and minor grooves.

What role do grooves in DNA play?

They create recognition surfaces for proteins involved in regulation and replication.

Why is strand separation essential in DNA?

It allows access to encoded sequence information for replication, transcription, and translation.

What is B-DNA's relevance in biological conditions?

It is the most biologically relevant form in aqueous and low-salt cellular conditions.

What is A-DNA?

A more compact helix that forms in lower water and higher salt conditions.

What is Z-DNA?

A left-handed helix that may occur at specific genomic sites with regulatory roles.

What is the primary function of DNA?

To replicate, store, express information, and allow variation.

How many base pairs do human cells copy per division?

Approximately 3 × 10⁹ base pairs.

What is the semiconservative model of DNA replication?

Each daughter duplex contains one parental and one newly synthesized strand.

What did the Meselson-Stahl experiment demonstrate?

It provided evidence for semiconservative replication of DNA.

What initiates DNA replication in bacteria?

Replication starts at a specific origin of replication, forming two replication forks.

What is the role of helicase in DNA replication?

It unzips the DNA helix by breaking hydrogen bonds to create single-stranded templates.

What is the function of topoisomerase during replication?

It prevents over-twisting ahead of the replication fork by cutting and resealing DNA.

What are SSB proteins?

Single-stranded binding proteins that prevent re-annealing or degradation of exposed DNA.

What is the difference between leading and lagging strands?

The leading strand is synthesized continuously, while the lagging strand is synthesized in short Okazaki fragments.

What is the role of DNA ligase?

It seals nicks in the DNA backbone, converting adjacent fragments into a continuous strand.

How do eukaryotic DNA replication processes differ from prokaryotic?

Eukaryotes have larger genomes and initiate replication at multiple origins simultaneously.

What is the function of telomeres?

They buffer genes from erosion caused by the lagging-strand priming constraint.

What is the 'end-replication problem'?

It refers to the shortening of telomeres during DNA replication in somatic cells.

What is the role of telomerase?

It extends telomeric repeats using an RNA template and is active in stem cells and some cancers.

What is DNA recombination?

A repair process for double-strand breaks using homologous chromosomes for accurate repair.

What are Holliday junctions?

Structures formed during double-strand break repair that can yield crossover or non-crossover products.