Introduction to Biology

• Biology is the scientific study of life.
• It explores structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms.
• Biology recognizes the cell as the basic unit of life.
• Genes serve as the basic unit of heredity.
• Evolution is the engine that propels the creation and extinction of species.
• Living organisms are open systems.
• Open systems survive by transforming energy and decreasing their local entropy.
• Biology includes a wide range of subdisciplines, each defined by the scale at which life is studied.

Subdisciplines of Biology

• Molecular biology studies complex interactions of biological systems, such as DNA, RNA, and proteins.
• Cell biology examines the structural and physiological properties of cells, including behaviors, interactions, and environment.
• Anatomy studies the physical structure of multicellular organisms and their parts.
• Physiology studies the mechanical, physical, and biochemical functions of living organisms.
• Genetics studies heredity and variation in organisms.
• Evolutionary biology studies the processes that produce the diversity of life on Earth, starting from a single common ancestor.
• Ecology studies the interactions of living organisms with one another and their environment.

Key Concepts in Biology

• Cell theory: the cell is the fundamental unit of life.
• Gene theory: traits are inherited through genes.
• Evolution: all life forms have evolved over time from a common ancestor through natural selection.
• Homeostasis: organisms maintain a stable internal environment.
• Energy: all life requires energy and matter.

Genetics

• Genetics is the scientific study of heredity and variation of inherited characteristics.
• Genetics plays a crucial role in understanding the molecular mechanisms of inheritance, gene expression, and evolution.

Central Dogma of Molecular Biology

• The central dogma of molecular biology describes the flow of genetic information within a biological system.
• DNA (deoxyribonucleic acid) is transcribed into RNA (ribonucleic acid), which is then translated into protein.
• This process is essential for gene expression and cellular function.

DNA Structure and Function

• DNA is a double-stranded helix composed of nucleotides.
• Each nucleotide contains a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).
• The sequence of these bases encodes genetic information.
• DNA replicates to pass on genetic information during cell division.
• The structure of DNA was elucidated by James Watson and Francis Crick in 1953.

Genes

• Genes are the fundamental units of heredity.
• They are segments of DNA that contain the instructions for making a specific protein or RNA molecule.
• Genes are organized on chromosomes, which are structures within cells that contain DNA.

Chromosomes

• Chromosomes are thread-like structures made of DNA and proteins, located in the nucleus of cells.
• Humans have 23 pairs of chromosomes, for a total of 46.
• One set of chromosomes is inherited from each parent.
• Chromosomes carry genetic information in the form of genes.
• During cell division, chromosomes replicate and are distributed to daughter cells, ensuring genetic continuity.
• Chromosomes exist as chromatin when the cell is not dividing.

Gene Expression

• Gene expression is the process by which the information encoded in a gene is used to synthesize a functional gene product (protein or RNA).
• It involves two main steps: transcription and translation.

Transcription

• Transcription is the process of synthesizing RNA from a DNA template.
• It is catalyzed by RNA polymerase.
• The resulting RNA molecule is called messenger RNA (mRNA).
• mRNA molecule carries the genetic code from the nucleus to the ribosomes.

Translation

• Translation is the process of synthesizing a protein from an mRNA template.
• It occurs on ribosomes, complex molecular machines found in the cytoplasm.
• Transfer RNA (tRNA) molecules bring amino acids to the ribosome.
• The amino acids are added to the growing polypeptide chain based on the sequence of codons in the mRNA.

Genetic Variation

• Genetic variation refers to differences in DNA sequences among individuals within a population.
• It is the raw material for evolution.
• Mutations, gene flow, and genetic recombination are the main sources of genetic variation.

Mutations

• Mutations are changes in the DNA sequence.
• They can occur spontaneously or be induced by environmental factors.
• Mutations can be beneficial, harmful, or neutral in their effects on an organism.
• They are the ultimate source of all new genetic variation.

Gene Flow

• Gene flow is the movement of genes between populations.
• It can introduce new alleles into a population or alter the allele frequencies in existing populations.
• Gene flow can reduce genetic differences between populations.

Genetic Recombination

• Genetic recombination is the process by which genes are rearranged to produce new combinations of alleles.
• It occurs during meiosis, the process of cell division that produces gametes (sperm and egg cells).
• Recombination increases genetic variation by creating offspring with different combinations of traits than their parents.

Mendelian Genetics

• Gregor Mendel's experiments with pea plants laid the foundation for the science of genetics.
• Mendel proposed that traits are inherited as discrete units, which we now call genes.
• Mendel's laws of inheritance include the law of segregation and the law of independent assortment.

Law of Segregation

• The law of segregation states that each individual has two alleles for each trait.
• These alleles separate during gamete formation.
• Each gamete receives only one allele for each trait.

Law of Independent Assortment

• The law of independent assortment states that the alleles for different traits segregate independently of each other during gamete formation.
• This law applies when the genes for different traits are located on different chromosomes or are far apart on the same chromosome.

Modern Synthesis

• The modern synthesis is the integration of Mendelian genetics with Darwinian evolution.
• It emphasizes the role of natural selection in shaping genetic variation within populations.
• The modern synthesis provides a comprehensive framework for understanding the evolution of life.