Molecular Biology Quiz

Molecular Biology

• Molecular biology is the branch of biology that studies gene structure and function at the molecular level, overlapping with genetics and biochemistry.
• The field primarily concerns interactions between DNA, RNA, and protein biosynthesis, as well as how these interactions are regulated.

Cells, Genome, Gene, and DNA

• Almost all cells of a living organism contain genetic information in the form of DNA.
• Cells from different parts of an organism have the same DNA.
• Unicellular organisms are prokaryotes, while multicellular organisms are eukaryotes.
• The genome refers to the total genetic information of an organism, encoded in DNA (or RNA for some viruses).
• A gene is the basic unit of inheritance, a segment of DNA containing information required for the synthesis of a functional biological product (protein or RNA).

DNA Structure and Function

• DNA is contained in the nucleus, arranged in 22 chromosomes, plus two sex chromosomes, with two copies of each (total 46 chromosomes).
• DNA is 99.9% identical to other humans and 98% to chimpanzees.
• DNA is about 2 meters long, which is so long that it would stretch to the sun and back 600 times; it is tightly packed in the nucleus.
• DNA carries the blueprint for life, duplicates for new cells, and makes proteins for biological functions.
• The DNA molecule is composed of two complementary strands, 5' C-G-A-T-T-G-C-A-A-C-G-A-T-G-C 3' and 3' G-C-T-A-A-C-G-T-T-G-C-T-A-C-G 5'.

Gene Structure

• A gene is a segment of DNA with specific instructions for the production of one specific protein.
• Genes are located on chromosomes at specific loci.
• Genes must have exons, a start site, a stop site, and a control region.

RNA and its Types

• RNAs have a broader range of functions, including:
  • Ribosomal RNAs (rRNAs) as components of ribosomes, synthesizing proteins.
  • Messenger RNAs (mRNAs) as intermediaries, carrying information for protein synthesis.
  • Transfer RNAs (tRNAs) as adapter molecules, translating mRNA information into amino acid sequences.
  • Other RNAs with special functions (snRNA, snoRNA, etc.).

Messenger RNA

• mRNA is composed of codons, groups of three nucleotides.
• Start and stop codons exist.
• mRNA is modified and travels out of the nucleus.

Translation

• Translation uses mRNA as a template to make proteins in ribosomes.
• One codon corresponds to one amino acid.

Proteins

• Proteins make up a huge proportion of cell components (after water).
• Proteins have many functions:
  • Structural (e.g., collagen in bone)
  • Enzymatic
  • Transmembrane receptors
  • Hormonal
• Proteins have four levels of structure.

Nucleotides Functions

• Serve as energy currency in metabolic transactions (ATP, GTP).
• Serve as second messengers of hormones and other extracellular stimuli (cAMP).
• Synthesize carbohydrates (UDP, CDP).
• Serve as coenzymes (NAD, NADP, FADH2).
• Store and transmit genetic information from one generation to the next.

Nucleotide Structure

• A nucleotide has three characteristic components:
  • A nitrogenous (nitrogen-containing) base
  • A pentose
  • One or more phosphates
• The molecule without a phosphate group is called a nucleoside.

Purines and Pyrimidines

• Both DNA and RNA contain two major purine bases (adenine, guanine) and two major pyrimidines.
• In DNA, the second common pyrimidine is thymine (T), while in RNA, it is uracil (U).

Unusual Bases

• Although nucleotides bearing major purines and pyrimidines are most common, both DNA and RNA contain some minor bases.
• Found in viral DNA, transfer RNA, and modified bases include methylation, glycosylation, acetylation, and reduction.

Nucleosides

• The addition of a pentose sugar to a base through a glycosidic bond produces a nucleoside.
• If the sugar is ribose, a ribonucleoside is produced; if the sugar is 2-deoxyribose, a deoxyribonucleoside is produced.
• Examples include adenosine, guanosine, cytidine, and uridine.

Nucleotides

• The addition of one or more phosphate groups to a nucleoside produces a nucleotide.
• Examples include nucleoside monophosphates (AMP), nucleoside diphosphates (ADP), and nucleoside triphosphates (ATP).