Cell Membrane Quiz

Cell Membrane

• The cell membrane is composed of phospholipids that form a bilayer.
• Phospholipids are amphipathic, meaning they have both polar and non-polar regions.
• The polar head region is hydrophilic and faces the water surrounding the membrane.
• The non-polar tail region is hydrophobic and faces the interior of the membrane.
• The cell membrane is selectively permeable, meaning it only allows certain substances to pass through.
• Substances found inside the cell with higher concentration, such as enzymes, glycogen, and potassium
• Substances found outside the cell with higher concentration, such as oxygen and sodium.

Movement Through The Cell Membrane

• Lipid-soluble substances, like dissolves like, can diffuse directly through the phospholipid bilayer.
• Water-soluble substances, like ions, can diffuse across the cell membrane only by passing through cell membrane channels.
• The cell membrane is known to be a fluid mosaic model because of the presence of different macromolecules.

Passive Membrane Transport

• Passive membrane transport does not require the cell to expend energy and includes diffusion, osmosis, and facilitated diffusion.

Diffusion

• It generally involves the movement of a substance in a solution down a concentration gradient, that is, from a region of high concentration to a region of low concentration.
• Leak channels are always open, allowing substances to move across the membrane.
• Gated channels are similar to door-like channels that open and close to allow substances to move across the membrane.

Osmosis

• Osmosis is the movement/diffusion of water, a solvent, across a selectively permeable membrane from a region of high water concentration to a region of low water concentration.
• Osmotic pressure is the force required to prevent movement of water across a selectively permeable membrane.
• It depends on the difference of the solution concentrations inside a cell to outside the cell.
• There are three types of solutions in relation to osmosis: hypotonic, isotonic, and hypertonic.

Hypotonic

• Hypo means "under".
• It is a solution with a LOWER SOLUTE CONCENTRATION than water concentration relative to the cytoplasm of the cell.
• Water moves by osmosis into the cell, causing it to swell, a condition known as lysis if the cell swells enough, it can cause a rupture.

Isotonic

• It is a solution with an equal solute concentration compared to that of the cytoplasm in the cell.
• The movement of water into and out of the cell is at equilibrium.

Hypertonic

• Hyper means “above”.
• It is a solution with a HIGHER SOLUTE CONCENTRATION than water concentration relative to the cytoplasm of the cell.
• Water moves by osmosis out of the cell, causing it to shrink or crenate.

Carrier-Mediated Transport

• Some water-soluble, electrically charged or large-sized particles cannot enter or leave through the cell membrane by diffusion. They require carrier proteins to facilitate their movement across the membrane.
• Carrier-mediated transport can be either passive or active.
• Passive transport: facilitated diffusion does not require energy. The carrier protein binds to the molecule and facilitates its movement across the membrane down the concentration gradient.
• Active transport: requires energy to move substances against their concentration gradient.

Active Membrane Transport

• Active membrane transport requires the cell to expend energy, usually in the form of ATP.
• It includes active transport, secondary active transport, endocytosis, and exocytosis.

Endocytosis

• It is a process that brings materials into cells using vesicles (GOING IN).
• It is a form of active transport.
• There are two types of endocytosis: phagocytosis (cell eating) and pinocytosis (cell drinking).

Exocytosis

• It is a process that releases materials from cells using vesicles (GOING OUT), a form of active transport.

Organelles: The Cell's Little Helpers

• Each organelle in the cell has a specific function that contributes to the overall functioning of the cell.

Nucleus

• It is the control center of the cell and is located near at the center of the cell.
• Bounded by a nuclear envelope.
• Nuclear membrane – contains nuclear pores.
• Nucleoli – diffuse bodies with no surrounding membrane.
• Nuclei – contains 23 pairs of chromosomes which consist of DNA and Proteins.
• Chromatin – when chromosomes are loosely coiled.

Ribosomes

• They are dense particles consisting of two subunits, each composed of ribosomal RNA and protein. The sites for protein synthesis. They are found at two locations:
• Free in the cytoplasm.
• Attached to rough endoplasmic reticulum.

Endoplasmic Reticulum

• It's a network of interconnected membranes within the cytoplasm of eukaryotic cells. It can be rough or smooth, depending on the presence or absence of ribosomes.
• Rough endoplasmic reticulum (RER). The presence of ribosomes on its surface creates a rough appearance. Its main function is protein synthesis and modification.
• Smooth endoplasmic reticulum (SER). It lacks ribosomes on its surface and is involved in lipid synthesis, detoxification, and calcium storage.

Golgi Apparatus

• It is a stack of flattened, membrane-bound sacs called cisternae, involved in processing, sorting, and packaging proteins and lipids produced by the endoplasmic reticulum.
• It is also involved in the synthesis of lysosomes.

Lysosomes

• They are membrane-bound organelles that contain enzymes for intracellular digestion.
• It breaks down worn-out organelles, cell debris, and ingested material, and is involved in the destruction of invading pathogens.

Mitochondria

• They are double-membrane-bound organelles that are the powerhouses of the cell, where ATP is produced through cellular respiration.
• They have their own DNA and ribosomes, suggesting an ancestral origin independent of the cell itself.

Cytoskeleton

• It is a network of protein filaments that provides structural support, maintains cell shape, and facilitates movement within the cell. It is composed of three main types of filaments:
• Microtubules are the largest among the three; they are involved in cell shape, movement of organelles, and cell division
• Microfilaments are involved in cell movement, muscle contraction, and cytokinesis.
• Intermediate filaments provide mechanical support, helping to maintain cell shape.

DNA: The Genetic Code of Life

• Deoxyribonucleic acid (DNA) is the molecule that contains the information that directs protein synthesis, a process called gene expression.
• DNA molecules are composed of nucleotides joined together to form two nucleotide strands.
• Each strand runs in an opposite direction, forming a double helix structure.
• The two strands are connected and resemble a ladder that is twisted along its axis.
• Each nucleotide consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
• There are 4 types of nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
• Each nucleotide on one DNA strand has a specific bonding pattern to another nucleotide on the opposite strand.
• This pairing rule is the basis for DNA replication and protein synthesis.

Test your knowledge about the structure and function of the cell membrane. This quiz covers key concepts including the composition of the phospholipid bilayer, selective permeability, and movement of substances across the cell membrane. Dive deep into the mechanisms that govern cellular interactions with their environment.