DNA Structure and Genes Overview

DNA Structure and Function

• DNA is a double helix comprised of a sugar-phosphate backbone and nitrogenous bases.
• The backbone consists of alternating deoxyribose sugar and phosphate molecules.
• The rungs of the ladder are nitrogenous bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G).
• DNA contains the instructions (genes) for building and operating an organism.
• Human cells possess approximately 120,000 genes, with roughly 40,000 actively used to create the organism's traits.
• The remaining 80,000 genes are currently deemed inactive.

Genes and Alleles

• A gene is a segment of DNA that codes for a specific protein.
• Alleles are variants of a gene, leading to variations in traits like eye color.
• Genotype refers to the set of alleles an organism possesses.
• Phenotype is the observable expression of traits, influenced by both genotype and environment.
• Homozygous dominant genotype contains two dominant alleles (e.g., AA).
• Homozygous recessive genotype possesses two recessive alleles (e.g., aa).
• Heterozygous genotype has one dominant and one recessive allele (e.g., Aa).

Cell Types and Reproduction

• Somatic cells form the body, diploid (2n) with two sets of chromosomes (one from each parent).
• Germ cells, which develop into gametes (sperm and egg), are also diploid but undergo meiosis to form haploid gametes (n).
• Gametes are haploid, with only one set of chromosomes.
• Fertilization of gametes produces a zygote, a single diploid cell.
• Heredity is the transmission of traits from parents to offspring via reproduction.

Chromosomes

• Chromosomes are structures made of DNA and proteins that carry genetic information; humans have 46 chromosomes.
• Sister chromatids are identical copies of a chromosome bound at the centromere.
• Homologous chromosomes are pairs of chromosomes (one from each parent) with genes for the same traits.

Nucleic Acids

• RNA is a single-stranded molecule that plays a central role in protein synthesis.
• RNA differs from DNA by using uracil (U) in place of thymine (T).
• The three major chemical groups within DNA are the sugar deoxyribose, the phosphate group, and the nitrogenous bases.

Protein Synthesis and the Central Dogma

• The central dogma outlines the flow of genetic information: DNA → RNA → protein.
• Transcription copies DNA's genetic code onto mRNA.
• Translation uses the mRNA code to assemble proteins at ribosomes.
• tRNA brings amino acids to the ribosome during protein synthesis, guided by mRNA.
• rRNA is part of the ribosome structure, catalyzing protein synthesis.

Other Important Concepts to Know

• Nondisjunction: Improper chromosome separation during meiosis, leading to aneuploidy (abnormal chromosome number).
• Trisomy is the presence of an extra chromosome, and monosomy the deficiency of one.
• Mutations include point mutations (alterations in single nucleotides) and chromosomal deletions.
• Polyploidy involves having more than two sets of chromosomes, common in plants.
• Meiosis is the type of cell division that produces four haploid gametes.
• Spermatogenesis is the process of sperm formation in males, and oogenesis is the process of egg formation in females.
• Histone proteins are responsible for packaging DNA in the nucleus.
• Non-coding DNA plays a role in cellular processes like gene regulation and structure.
• Epigenetics studies how environmental factors affect gene expression without altering the DNA sequence.
• A Karyotype is a visual representation of an organism's chromosomes, useful in detecting chromosomal abnormalities.
• Autosomes are non-sex chromosomes; humans have 22 pairs.

Explore the fundamental concepts of DNA structure and its functions, including the roles of genes and alleles. Learn about the double helix, the sugar-phosphate backbone, and how variations in genes impact traits. This quiz will test your knowledge on genetic concepts essential for understanding biology.