Biology Fundamentals: Cells, DNA, Enzymes, and Organisms
Foundational Concepts in Biology
Organism, Population, and Community Defined
An organism is a single living thing. A population consists of all organisms of the same species in the same place at the same time. A community comprises all populations of different species coexisting in the same place at the same time.
Biological Levels of Organization
Life is organized into hierarchical levels, from the smallest components to the largest systems:
- Organelle
- Cells
- Tissues
- Organs
- Organ Systems
- Organisms
- Populations
- Communities
- Ecosystem
- Biosphere
The Cell: Basic Unit of Life
Defining the Cell
The cell is the fundamental building block and the most basic component of all living things.
Key Components of a Cell
Essential parts of a typical cell include:
- Plasma membrane
- Cytoplasm
- Ribosomes
- DNA
Biomolecules: Structure and Function
Biomolecules: Building Blocks and Sources
The four major biomolecules and their respective building blocks are:
- Lipids: Fatty acids and glycerol
- Proteins: Amino acids
- Carbohydrates: Monosaccharides (simple sugars)
- Nucleic Acids: Nucleotides
Functions of Key Biomolecules
- Lipids: Function in the body for energy storage, insulation, and as structural components of cell membranes.
- Carbohydrates: Primarily serve as the body’s main source of energy.
- Nucleic Acids: Essential for storing and transmitting genetic information (DNA and RNA).
- Proteins: Act as the ‘workhorses’ of the body, performing a vast array of functions including structural support, enzymatic reactions, transport, and defense.
Genetics: DNA and RNA
DNA’s Four Nitrogenous Bases
The four nitrogenous bases found in DNA are:
- Adenine (A)
- Cytosine (C)
- Guanine (G)
- Thymine (T)
RNA’s Four Nitrogenous Bases
The four nitrogenous bases found in RNA are:
- Adenine (A)
- Cytosine (C)
- Guanine (G)
- Uracil (U)
Fundamental DNA Structure
The basic structural unit of DNA is a nucleotide, which consists of three components:
- A deoxyribose sugar (carbon sugar)
- A nitrogenous base
- A phosphate group
RNA Structure: Single-Stranded Nature
The RNA molecule is typically single-stranded, unlike DNA which forms a double helix structure.
Enzymes: Catalysts of Life
Classes of Enzymes
Enzymes are categorized into several classes based on the reactions they catalyze. These include:
- Hydrolases
- Oxidoreductases
- Lyases
- Transferases
- Ligases
- Isomerases
First Enzyme in Human Digestion
The first enzyme that food comes in contact with in the human body is amylase, specifically salivary amylase, which begins carbohydrate digestion.
Importance of Enzymes in the Body
Enzymes are crucial to the body because they help facilitate and speed up biochemical reactions, making life processes possible.
Enzyme-Substrate Interaction
The specific molecule on which an enzyme acts is called a substrate.
Factors Influencing Enzyme Activity
Several factors can significantly affect the activity of enzymes:
- Temperature
- pH level
- Enzyme concentration
- Substrate concentration
- Inhibitor concentration
Cellular Processes and Microorganisms
Organisms Capturing Non-Living Energy
Organisms that capture energy from non-living sources, such as sunlight or chemical reactions, are called autotrophs.
Cellular Energy Carrier Molecule
The primary energy-carrying molecule that cells use for most cellular processes is Adenosine Triphosphate (ATP). ATP is vital for energy transfer in all living cells.
Cellular Engulfment: Endocytosis
Cells engulf external substances, including microorganisms, through a process called endocytosis.
Phagocytosis: A Form of Endocytosis
Specific microorganisms or larger particles can enter the cell through phagocytosis, which is a specialized type of endocytosis often referred to as ‘cell eating’.
Smallest Microorganism Identified
Among microorganisms, viruses are generally considered the smallest.
Corrections and Clarifications in Biology
Fundamental Unit of Life
Correction: The most basic unit of life is a cell, not an organ. Organs are composed of multiple tissues, which are in turn made of cells.
Organelles in Unicellular Organisms
Clarification: Unicellular organisms like bacteria (prokaryotes) do not contain membrane-bound organelles, but they do possess ribosomes, which are essential for protein synthesis.
Initiating DNA Replication
The initial step in DNA replication involves ‘unzipping’ or unwinding the double helix structure of the DNA molecule, separating the two strands.
Clarifying DNA Replication vs. Expression
Correction: DNA replication is the process by which DNA makes an exact copy of itself during cell division. DNA expression (or gene expression) is the process where genetic information encoded in DNA is used to synthesize functional products, such as proteins or RNA.
Leading Strand Orientation in DNA
During DNA replication, the leading strand is synthesized continuously and is oriented in the 5′ to 3′ direction, moving towards the replication fork.
DNA Polymerase Action on Leading Strand
DNA polymerase binds to the leading strand, continuously adding new complementary nucleotides in the 5′ to 3′ direction.
Leading and Lagging Strands in Replication
During DNA replication, the leading strand is synthesized as a continuous piece. The other strand, known as the lagging strand, is synthesized in small, discontinuous fragments called Okazaki fragments.
Catabolism vs. Anabolism: Energy Processes
Metabolic processes are broadly divided into two types:
- Anabolism: Requires energy to build complex molecules from simpler ones (e.g., growth and synthesis).
- Catabolism: Releases energy by breaking down complex molecules into simpler ones (e.g., digestion and cellular respiration).
Biological Classification: Kingdoms and Ranks
Correction: The seven main taxonomic ranks for classifying living things are Kingdom, Phylum, Class, Order, Family, Genus, and Species. The terms ‘animal, plant, fungi, protist, and monera’ refer to biological kingdoms (or historical kingdoms), which are broad categories of life.
Insights into Viruses and Bacteria
Viral Entry Mechanisms
Viruses can enter the human body through various mechanisms and routes, including respiratory droplets, contaminated food/water, direct contact, and vectors.
Viral Spikes: Cell Recognition
The spikes on the surface of a virus are crucial for recognizing and binding to specific receptor proteins on host cells, facilitating the initial step of infection.
Viral Reproduction: Intracellular Requirement
Correction: Viruses are obligate intracellular parasites, meaning they can only reproduce inside a living host cell, utilizing the host’s cellular machinery.
Common Bacterial Shapes
Bacteria commonly exhibit three main shapes:
- Spherical: Known as cocci (e.g., streptococcus)
- Rod-like: Known as bacilli (e.g., E. coli)
- Curved: Includes spirilla (spiral-shaped) and vibrios (comma-shaped)
Bacterial Reproduction: Binary Fission
Bacteria primarily reproduce asexually by dividing into two genetically identical daughter cells, a process known as binary fission.