DNA Structure and Genes Overview

Study Notes

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.

Description

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.