Cell Structure and Function Overview

Prokaryotic Cells

Unicellular organisms that lack a nucleus and membrane-bound organelles, generally smaller than eukaryotic cells.

Eukaryotic Cells

Cells that contain membrane-bound organelles, including a nucleus, and can be unicellular or multicellular.

Nucleus

The control center of the cell that stores genetic material and regulates cellular activities.

Nucleolus

A dense structure within the nucleus that produces ribosomal RNA and assembles ribosomes.

Ribosomes

Cellular structures that synthesize proteins by translating messenger RNA sequences.

Rough ER

Endoplasmic reticulum with ribosomes on its surface, involved in protein folding and modification.

Smooth ER

Endoplasmic reticulum that synthesizes lipids and detoxifies drugs, lacking ribosomes.

Golgi Apparatus

Modifies, sorts, and packages proteins and lipids for transport within and outside the cell.

Mitochondria

Organelles that generate ATP through aerobic respiration and contain their own DNA.

Chloroplasts

Organelles that conduct photosynthesis in plant cells, converting light energy into chemical energy.

Lysosomes

Cell organelles that contain digestive enzymes for waste processing and recycling.

Peroxisomes

Organelles that break down fatty acids and neutralize toxic compounds like hydrogen peroxide.

Vacuoles

Storage organelles that contain water, nutrients, and waste materials, especially large in plant cells.

Cytoskeleton

A network providing structural support and facilitating transport and motility within the cell.

Microtubules

Cytoskeletal components that form spindle fibers and are involved in cell movement and structure.

Centrioles

Cylindrical structures organizing microtubules for cell division, found in pairs within the centrosome.

Plasma Membrane

The selectively permeable barrier regulating substance movement into and out of the cell.

Passive Transport

Movement of molecules across a membrane without ATP, relying on concentration gradients.

Simple Diffusion

Movement of small, nonpolar molecules from high to low concentration until equilibrium is achieved.

Facilitated Diffusion

Movement of larger or charged molecules across a membrane via transport proteins, without ATP.

Osmosis

The movement of water across a selectively permeable membrane. from an area of high water concentration to an area of low water concentration. A passive process that doesn’t require ATP/energy

Hypotonic

a solution with a lower concentrations of solutes (salt/sugar) (indicating a higher concentration of water) compared to another solution or a cell’s cytoplasm, causing water to move into the cell.

Hypertonic

A solution with higher solute concentration compared to the cell; water moves out of the cell.

Isotonic

A solution where solute concentrations are equal inside and outside the cell; no net water movement.

Active Transport

Movement of substances against their concentration gradient, requiring ATP.

Sodium-Potassium Pump

An active transport mechanism moving 3 Na⁺ out and 2 K⁺ into the cell, crucial for cell function.

Endocytosis

The process by which cells engulf materials into vesicle formation from the plasma membrane.

Phagocytosis

The ingestion of large particles or cells, known as 'cell eating'.

Pinocytosis

The ingestion of extracellular fluid and dissolved solutes, termed 'cell drinking'.

Receptor-Mediated Endocytosis

A selective form of endocytosis where specific molecules bind to receptors before internalization.

Exocytosis

Process where vesicles fuse with the plasma membrane to release their contents outside the cell.

DNA Replication

A semi-conservative process where each new DNA molecule consists of one parent and one new strand.

Helicase

The enzyme that unwinds and separates the two strands of DNA during replication.

Primase

Enzyme that synthesizes short RNA primers for starting DNA synthesis.

DNA Polymerase III

The main enzyme adding complementary nucleotides during DNA replication.

DNA Polymerase I

Removes RNA primers and replaces them with DNA nucleotides in newly synthesized DNA.

Ligase

Enzyme that seals gaps between Okazaki fragments, forming a continuous DNA strand.

Topoisomerase

Enzyme preventing supercoiling of DNA by cutting and rejoining strands during replication.

Transcription

Process where DNA is transcribed into messenger RNA (mRNA); occurs in the nucleus of eukaryotes.

Initiation (Transcription)

RNA polymerase binds to the promoter region to start transcription.

Elongation (Transcription)

RNA polymerase synthesizes mRNA by adding complementary RNA nucleotides.

Termination (Transcription)

Transcription ends when RNA polymerase reaches a terminator sequence, releasing the mRNA.

Translation

Process of synthesizing proteins from mRNA at the ribosome, interpreting codons to assemble amino acids.

Initiation (Translation)

The ribosome assembles on mRNA at the start codon, with the first tRNA carrying methionine.

Elongation (Translation)

tRNA brings specific amino acids to the ribosome, elongating the polypeptide chain.

Termination (Translation)

Polypeptide synthesis stops at a stop codon; the completed polypeptide is released.

Law of Segregation

Each individual carries two alleles for each trait; alleles segregate during gamete formation.

Law of Independent Assortment

Genes for different traits assort independently during gamete formation, allowing genetic variation.

Incomplete Dominance

Phenotype of a heterozygote is intermediate between two homozygous phenotypes.

Codominance

Both alleles in a heterozygote are fully expressed, resulting in a phenotype showing both traits.

Polygenic Traits

Traits influenced by multiple genes, resulting in a continuum of phenotypes.

Epistasis

Interaction between genes where one gene masks or suppresses another's expression.

Tundra

A cold biome with a short growing season and low biodiversity, mainly mosses and lichens.

Desert

A biome defined by extreme dryness and temperature variances with specialized flora and fauna.

Tropical Rainforest

A high biodiversity biome with warm temperatures and heavy rainfall, supporting dense vegetation.

Producers (Autotrophs)

Organisms, typically plants, that convert sunlight into chemical energy through photosynthesis.

Primary Consumers

Herbivores that eat producers, crucial for energy transfer in ecosystems.

Secondary Consumers

Carnivores that feed on primary consumers, bridging energy transfer up the food chain.

Tertiary Consumers

Apex predators at the top of the food chain, maintaining ecological balance.

Decomposers

Organisms like fungi and bacteria that break down dead matter, recycling nutrients in the ecosystem.

Exponential Growth

Population growth characterized by a J-shaped curve, indicating rapid growth with unlimited resources.

Logistic Growth

Population growth represented by an S-shaped curve, stabilizing at environmental carrying capacity.

C3 Plants

Utilize the Calvin cycle for photosynthesis; thrive in moderate climates like wheat and rice.

C4 Plants

Adapted to hot, dry environments, reducing photorespiration and improving CO2 capture, e.g., corn.

CAM Plants

Plants that conserve water by opening stomata at night for CO2 uptake, e.g., cacti.

Auxins

Plant hormones that promote cell elongation, influencing growth toward light and gravity.

Gibberellins

Plant hormones stimulating growth processes like seed germination and flowering.

Cytokinins

Hormones promoting cell division and influencing plant growth and development.

Ethylene

A gaseous hormone regulating fruit ripening and promoting processes like leaf abscission.