2.1 Cellular Structure and Function
3 min read•august 7, 2024
Cells are the building blocks of life, forming the foundation of human physiology. Understanding their structure and function is crucial for grasping how our bodies work at the most basic level.
From the to the , each part plays a vital role in keeping us alive. We'll explore how cells communicate, generate energy, and create proteins, connecting these processes to the broader picture of human anatomy and physiology.
Cell Structure
Cell Membrane and Cytoplasm
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- Cell membrane consists of a phospholipid bilayer with embedded proteins that separates the interior of the cell from the outside environment
- Selectively permeable membrane controls the passage of substances in and out of the cell (ions, nutrients, waste products)
- is the gelatin-like fluid inside the cell where organelles are suspended
- Contains , a network of filaments and tubules that provides structure, support, and movement to the cell (actin filaments, microtubules)
Nucleus and Endoplasmic Reticulum
- Nucleus is the control center of the cell, containing the cell's genetic material (DNA) and directing cellular activities
- is a double membrane that surrounds the nucleus, separating it from the cytoplasm
- (ER) is a network of membranous tubes and sacs that extends from the nuclear envelope
- is studded with and is involved in and transport
- Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage
Mitochondria, Golgi Apparatus, and Other Organelles
- are the powerhouses of the cell, generating through (converting glucose and oxygen into energy)
- is a stack of flattened membrane sacs that modifies, packages, and distributes proteins and lipids (secretory pathway)
- are membrane-bound organelles containing digestive enzymes that break down cellular waste, debris, and foreign invaders (intracellular digestion)
- are organelles that detoxify harmful substances and break down fatty acids (liver cells)
- is an organelle that organizes the cell's microtubules and is involved in cell division (mitotic spindle)
Cell Functions
Cell Signaling and Membrane Transport
- involves communication between cells through chemical messengers (, ) that bind to on the cell surface
- is the movement of substances across the cell membrane
- occurs without energy input and includes (movement of small, nonpolar molecules) and (movement of larger, polar molecules through protein channels)
- requires energy (ATP) to move substances against their concentration gradient ()
Cellular Respiration and Protein Synthesis
- Cellular respiration is the process of breaking down glucose to generate ATP, the cell's energy currency
- Occurs in the mitochondria and involves (cytoplasm), (mitochondrial matrix), and (inner mitochondrial membrane)
- Protein synthesis is the process of creating new proteins based on the genetic instructions in DNA
- occurs in the nucleus, where DNA is transcribed into
- occurs in the cytoplasm, where ribosomes read the mRNA and assemble into (proteins)
Key Terms to Review (35)
Active transport: Active transport is the process by which cells move molecules against their concentration gradient, utilizing energy typically from ATP. This mechanism is essential for maintaining cellular homeostasis, allowing cells to accumulate nutrients and remove waste products despite unfavorable concentration differences. Active transport is crucial in many physiological processes, including nutrient absorption and ion regulation in cells.
Amino Acids: Amino acids are organic compounds that serve as the building blocks of proteins, essential for various biological processes. They consist of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable R group that determines the identity and properties of each amino acid. Their role in protein synthesis and cellular function highlights their importance in maintaining life.
ATP: Adenosine triphosphate (ATP) is a nucleotide that serves as the primary energy carrier in all living organisms. It plays a crucial role in cellular metabolism, allowing cells to perform essential functions by providing the energy required for biochemical reactions, such as muscle contraction, nerve impulse propagation, and biosynthesis of macromolecules. ATP is often referred to as the 'molecular unit of currency' of intracellular energy transfer.
Cell membrane: The cell membrane is a biological barrier that surrounds and protects the cell, regulating what enters and exits the cell. It consists mainly of a phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates, playing a crucial role in maintaining homeostasis and facilitating communication between cells.
Cell Signaling: Cell signaling is the process by which cells communicate with each other to coordinate their actions, allowing for responses to changes in their environment. This communication can involve various signaling molecules, receptors, and pathways that ensure cells work together effectively to maintain homeostasis and facilitate processes such as growth, immune response, and metabolism.
Cellular respiration: Cellular respiration is a metabolic process by which cells convert nutrients into energy in the form of adenosine triphosphate (ATP), utilizing oxygen and producing carbon dioxide and water as byproducts. This process is essential for maintaining cellular function and energy balance, allowing cells to perform various functions necessary for life, including growth, repair, and maintenance.
Centrosome: A centrosome is a cellular structure that serves as the main organizing center for microtubules and plays a crucial role in cell division by facilitating the formation of the mitotic spindle. It is composed of a pair of centrioles surrounded by a matrix of proteins, which helps in the assembly and anchoring of microtubules. Centrosomes are essential for maintaining the overall architecture of the cell and ensuring accurate chromosome segregation during cell division.
Cytoplasm: Cytoplasm is the gel-like substance found between the cell membrane and the nucleus, encompassing all the organelles and cell structures except for the nucleus itself. This area is crucial for maintaining cell shape, facilitating cellular processes, and supporting the functions of various organelles. The cytoplasm plays a vital role in cell metabolism and is involved in the movement of materials within the cell, as well as communication with the external environment.
Cytoskeleton: The cytoskeleton is a complex network of fibers that provides structural support, shape, and organization to cells. It plays a critical role in cellular processes such as movement, division, and intracellular transport, serving as a scaffold that helps maintain the cell's integrity and facilitates communication between its various components.
Electron transport chain: The electron transport chain (ETC) is a series of protein complexes and other molecules found in the inner mitochondrial membrane that play a crucial role in cellular respiration. It facilitates the transfer of electrons from electron donors to electron acceptors, which results in the production of adenosine triphosphate (ATP) through oxidative phosphorylation. The process is essential for converting energy stored in nutrients into a usable form for cellular functions.
Endoplasmic reticulum: The endoplasmic reticulum (ER) is an extensive network of membranous tubules and sacs within eukaryotic cells, playing a crucial role in the synthesis, folding, modification, and transport of proteins and lipids. The ER can be classified into two types: rough ER, which is studded with ribosomes and primarily involved in protein synthesis, and smooth ER, which is involved in lipid synthesis and detoxification processes. This organelle is essential for maintaining cellular function and homeostasis.
Facilitated diffusion: Facilitated diffusion is a passive transport process that allows substances to cross membranes with the help of specific transport proteins. Unlike simple diffusion, which occurs directly through the lipid bilayer, facilitated diffusion utilizes carrier or channel proteins to assist molecules that cannot easily pass through the cell membrane due to their size or polarity. This process is essential for maintaining cellular homeostasis and transporting vital substances into and out of cells.
Glycolysis: Glycolysis is the metabolic process that converts glucose into pyruvate, producing a net gain of two ATP molecules and two NADH molecules in the process. This pathway occurs in the cytoplasm of cells and is crucial for cellular respiration, linking carbohydrate metabolism to energy production.
Golgi apparatus: The Golgi apparatus is a membrane-bound organelle found in eukaryotic cells that is essential for processing and packaging proteins and lipids for secretion or delivery to other organelles. It plays a critical role in modifying, sorting, and shipping molecules synthesized in the endoplasmic reticulum, ensuring that they are correctly directed to their destinations within or outside the cell.
Hormones: Hormones are chemical messengers produced by glands in the endocrine system that regulate various physiological processes in the body, including growth, metabolism, and mood. They travel through the bloodstream to target organs and tissues, influencing many bodily functions and maintaining homeostasis.
Krebs Cycle: The Krebs Cycle, also known as the citric acid cycle or TCA cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA. This cycle takes place in the mitochondria and plays a critical role in cellular respiration, linking carbohydrate, fat, and protein metabolism while producing key energy-carrying molecules such as NADH and FADH2.
Lysosomes: Lysosomes are membrane-bound organelles found in animal cells that contain digestive enzymes responsible for breaking down waste materials and cellular debris. These organelles play a crucial role in cellular homeostasis by facilitating the degradation and recycling of macromolecules, thereby maintaining the health of the cell.
Membrane transport: Membrane transport refers to the processes by which substances move across cellular membranes, allowing for the maintenance of homeostasis and the exchange of materials between the cell and its environment. This involves mechanisms that can be passive, such as diffusion and osmosis, or active, requiring energy input to move substances against their concentration gradient. Understanding membrane transport is crucial for grasping how cells interact with their surroundings, uptake nutrients, expel waste, and respond to external signals.
Mitochondria: Mitochondria are membrane-bound organelles found in the cytoplasm of eukaryotic cells, often referred to as the 'powerhouses' of the cell. They are primarily responsible for producing adenosine triphosphate (ATP), the main energy currency of the cell, through a process known as oxidative phosphorylation. Beyond energy production, mitochondria also play key roles in cellular metabolism, regulation of the cell cycle, and apoptosis (programmed cell death).
MRNA: mRNA, or messenger RNA, is a single-stranded nucleic acid that carries genetic information from DNA to the ribosome, where proteins are synthesized. This process, known as transcription and translation, is crucial for cellular function as mRNA serves as a template that dictates the amino acid sequence of proteins, which are essential for various cellular processes and functions.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals across synapses between neurons, playing a crucial role in communication within the nervous system. These molecules are released from the presynaptic neuron and bind to specific receptors on the postsynaptic neuron, facilitating various physiological responses, influencing mood, behavior, and overall brain function. Their dynamic interaction is essential for processes such as learning, memory, and emotional regulation.
Nuclear envelope: The nuclear envelope is a double-membrane structure that surrounds the nucleus of eukaryotic cells, separating the genetic material from the cytoplasm. It plays a crucial role in maintaining the integrity of the nucleus and regulating the exchange of materials between the nucleus and the cytoplasm, ensuring that essential processes such as gene expression and DNA replication occur within a controlled environment.
Nucleus: The nucleus is a membrane-bound organelle found in eukaryotic cells that houses the cell's genetic material, primarily in the form of DNA. It serves as the control center of the cell, regulating gene expression and mediating the replication of DNA during the cell cycle. The nucleus plays a critical role in maintaining the integrity of genes and controlling cellular activities.
Passive Transport: Passive transport is the movement of molecules across a cell membrane without the need for energy input, driven by the concentration gradient. This process allows substances to naturally flow from areas of higher concentration to areas of lower concentration, which is essential for maintaining homeostasis within the cell. It involves various mechanisms such as diffusion, facilitated diffusion, and osmosis that contribute to cellular function and nutrient uptake.
Peroxisomes: Peroxisomes are small, membrane-bound organelles found in the cytoplasm of eukaryotic cells that play a crucial role in lipid metabolism and detoxification of harmful substances. They contain enzymes that catalyze oxidative reactions, helping to break down fatty acids and detoxify hydrogen peroxide, a byproduct of metabolism. Their function is vital for maintaining cellular health and energy production.
Polypeptide Chains: Polypeptide chains are long sequences of amino acids linked together by peptide bonds, forming the building blocks of proteins. These chains fold into specific three-dimensional shapes that determine a protein's function within the cell, playing crucial roles in various biological processes. The unique sequence of amino acids in a polypeptide chain directly influences its structure and function, making them essential components of cellular machinery.
Protein synthesis: Protein synthesis is the biological process through which cells generate new proteins, essential for various functions, including structure, enzymes, and signaling. This intricate process involves two main stages: transcription, where DNA is converted into mRNA, and translation, where the mRNA is used to build a protein with the help of ribosomes and transfer RNA (tRNA). Understanding this process reveals how genetic information is translated into functional molecules that carry out critical cellular tasks.
Receptors: Receptors are specialized protein molecules located on cell surfaces or within cells that bind to specific signaling molecules, initiating a cellular response. They play a crucial role in communication between cells and their environment, allowing cells to detect and respond to various stimuli, such as hormones, neurotransmitters, and environmental changes. Receptors are essential for maintaining balance within biological systems and facilitating physiological control mechanisms.
Ribosomes: Ribosomes are molecular machines found within all living cells that serve as the site of protein synthesis. They translate messenger RNA (mRNA) sequences into polypeptide chains, which fold into functional proteins essential for cellular processes. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, highlighting their role in both free and membrane-bound protein production.
Rough ER: The rough endoplasmic reticulum (rough ER) is a type of organelle found in eukaryotic cells that is involved in the synthesis and processing of proteins. It is characterized by its surface, which is studded with ribosomes, giving it a 'rough' appearance under a microscope. This organelle plays a vital role in the production of proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle called the lysosome.
Simple diffusion: Simple diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration without the need for energy or assistance from proteins. This passive transport mechanism is essential for maintaining cellular homeostasis, allowing vital substances such as oxygen and carbon dioxide to passively exchange across cell membranes, which are primarily composed of phospholipids and proteins.
Smooth endoplasmic reticulum (smooth ER): The smooth endoplasmic reticulum (smooth ER) is a network of tubular membranes within the cell's cytoplasm that plays a vital role in lipid synthesis, metabolism, and detoxification. Unlike its rough counterpart, the smooth ER lacks ribosomes on its surface, giving it a smooth appearance, and it is involved in the production of hormones, storage of ions, and processing of various substances critical for cellular functions.
Sodium-potassium pump: The sodium-potassium pump is a vital membrane protein that actively transports sodium ions out of and potassium ions into cells, maintaining essential electrochemical gradients. This process is crucial for various cellular functions, including nerve impulse transmission and muscle contraction, as it helps to establish and maintain the resting membrane potential of cells.
Transcription: Transcription is the biological process in which the DNA sequence of a gene is copied into messenger RNA (mRNA). This process is essential for gene expression, as it serves as the first step in converting genetic information into functional proteins, connecting the molecular blueprint of an organism to its cellular activities.
Translation: Translation is the biological process through which the genetic code contained in messenger RNA (mRNA) is used to synthesize proteins. This process occurs in the ribosome and involves the decoding of the mRNA sequence into a specific sequence of amino acids, ultimately forming functional proteins essential for cellular structure and function.