Cell biology

Advantages of Multicellularity

Includes larger body size, distribution of labour among specialized cells, resilience to loss of cells, and increased surface area for exchanges.

Three types of plant tissues

Dermal tissue: Protection and regulation of molecular exchange with environment

Vascular tissue: Long distance transport

Ground tissue: Biosynthesis and storage

Cellular components of plant leaves

Stomata: Leaf epidermis which controls gas exchange

Mesophyll cells: contain chloroplasts for photosynthesis.

Veins: Transport water, nutrients, sugars, and signalling molecules.

Cellular component of plant roots

Apical meristem protected by root cap

Root cap that secretes mucilaginous polysaccharides which facilitate growth of root through the soil.

Root hairs that take in water and nutrients.

Pluripotency

The ability of plant cells to dedifferentiate and redifferentiation to a new cell type which allows plants to repair damaged tissue - necessary due to the rigidity of cell walls.

Apical vs Lateral meristem 

Apical - produce elongation, found in shoot and root tips.

Lateral - produces lateral growth (growing wider), found in stems in roots.

Caspian Strip

ring of material around plant cell that makes the wall impregnable - inhibits the passage of molecules and functions like a tight molecule. Often seen in roots - water can travel through it because of symplastic flow and osmosis

kinesins and dyneins

Motor proteins that move along microtubules via ATP hydrolysis - they move organelles in opposite directions.

Microtubule based movement

intracellular motor proteins and extra cellular cilia and flagella

Pitstop

compound that blocks clathrin function during endocytosis - can inhibit entry of HIV into human cells

Microtubules in animals vs plants

Animals - originate in centromere, one end embedded in centrosome and it grows out into cytoplasm.

Plants - form dynamic parallel arrays in the cortical cytoplasm adjacent to plasma membrane, none in the central part of the cell.

Transport vesicles

Cell membrane buds off to form a vesicle which are coated in clathrin monomer which attracts clathrin protein which will form a curved surface around the vesicle until it forces it to pinch off and form a sphere which will transport different materials.

Structure of Golgi apparatus

4-10 disc-shaped stacks (cisternae), number varies with function of cell - moves around the cell and are located in particular sites such as nucleus and ER network.

Function of Golgi apparatus

Each stack has distinct polarity, one side of the stack faces the ER and is the cis (receiving) face, proteins and glycoproteins made in the ER are transported in small transport vesicles that bud off the ER membrane and fuse with the cis face of the sack - proteins gained in cis face then move through apparatus to trans face in which they mature and modify - matured molecules are then sorted and packaged in vesicles at the trans face and are sent off to various destinations.

Endosymbiotic bacteria

Free-living bacteria that were engulfed by a host cell and eventually evolved into organelles like mitochondria and chloroplasts, forming a symbiotic relationship.

Amyloplast

Plastids for energy storage in underground plants such as roots and tubers, lacks coloured pigment, and produces and stores starches

Chromoplasts

synthesise and store carotenoid pigments, responsible for yellow, red, and orange pigments in plants.

Peroxisomes

Organelle that deals with toxic glycolate produced by the oxygenase reaction of rubisco in the calvin cycle in chloroplasts - in animal cells they oxidatively degrade molecules such as fatty acids.

How do peroxisomes work

Contain enzymes that transfer hydrogen atoms from products and add them to oxygen to make hydrogen peroxide - catalase enzyme then uses hydrogen peroxide to break down other substances - and then convert hydrogen peroxide back into water and oxygen so it can’t damage other molecules.

Process of photosynthesis

Chlorophylls absorb sunlight, photons from sunlight excite the electrons in chlorophylls, leading to a chain reaction of excited states until it reaches chlorophyll a. an excited electron is transferred to primary electron acceptor and goes through electron transport chain - energy from this used to move protons into lumen - diffusion of protons back into stroma via ATP synthase generates ATP.

Structure of chloroplast

Double membrane envelope, with an inner and outer membrane. Inside is the stroma, a fluid-filled space containing thylakoids, which are flattened sacs often stacked into grana. Chlorophyll is embedded in the thylakoid membranes.

Autophagy

The process by which cells recycle their own organelles and proteins.

Nuclear pores

Channels that perforate the inner and outer membranes regulating the movement of molecules between the cytosol and the nucleoplasm - containing about 30 different proteins, approx 50nm in diameter. Regulates transport of DNA, RNA, and mRNA but allows small molecules to flow freely.

DNA

DNA winds around histone proteins to form nucleosomes which then twist into strands of chromatin which condenses into chromosomes

Histone

Protein that provides structural support to chromosomes as negatively charges DNA wraps around the positively charged protein.

Where in the mitochondria is ATP synthesised

ATP synthase is embedded within the inner membrane, protons are pumped into the space between the inner and outer membrane via electron transport chain, and then flow back through ATP synthase into matrix to generate ATP.

Calvin Cycle

A process in photosynthesis that produces glyceraldehyde 3-phosphate (G3P) by carbon fixation → carbon reduction → regeneration of starting molecule (Rubisco)

Cell Differentiation

The process where cells in multicellular organisms become distinct from one another, leading to specialized cell types.

Cell Division

The process by which a parent cell divides into two or more daughter cells, including mitosis and cytokinesis.

Cell Theory

The fundamental principles stating that all living organisms are composed of cells, every cell arises from preexisting cells, and the cell is the fundamental organizational unit of life.

Cell fractionation

A technique that separates cellular components based on their size and density.

Cell wall

A rigid outer layer found in plant cells, providing support and protection.

Centrosome

An organelle that organizes microtubules and is important for cell division.

Chloroplasts

Type of plastid - Organelle that contains chlorophyll (light absorbing pigment) and is responsible for photosynthesis.

Chromatin

The complex of DNA and proteins that forms chromosomes within the nucleus.

Cilia

Short, hair-like structures that sweep materials across cell surfaces, typically found on many cells with same internal structure as flagella

Confocal Microscopy

Uses monochromatic light from a high-intensity laser and a pinhole to prevent out-of-focus light, allowing for a sharp image with increase resolution and 3D imaging

Contrast

The visible difference in brightness between the light and dark areas within parts of a sample, crucial for imaging details.

Contrast

The visible differences within parts of a sample, crucial for imaging details.

Cytoplasm

A semifluid matrix known as cytosol containing subcellular organelles within a cell.

Cytoskeleton

A network of fibers that helps maintain the shape of the cell, enables movement, and organizes cellular components.

Desmosomes

Cell junctions that mechanically attach adjacent cells to each other.

Electron microscopy (EM)

A type of microscopy that uses electron beams to achieve high-resolution images of specimens.

Electron Microscopes (EM)

Microscopes that use electron beams for higher resolution and detail compared to light microscopes.

Endocytosis

The mechanism by which cells internalize substances from their external environment by engulfing them.

Endomembrane system

A collection of membranous structures involved in the synthesis, modification, and transport of proteins and lipid in which molecules can move from one to another by direct connection or transfer in small transport vesicles.

Endoplasmic Reticulum (ER)

A network of membranous tubules that extend through the cytoplasm involved in synthesizing proteins (rough ER) and lipid synthesis (smooth ER).

Endosymbiont theory

A theory explaining the origin of mitochondria and chloroplasts as symbiotic relationships between early eukaryotes and prokaryotes.

Endosymbiosis

The theory explaining the origin of mitochondria, suggesting they were once free-living bacteria that were engulfed by ancestral eukaryotic cells.

Eukaryotic Cells

Complex cells with membrane bound organelles, DNA enclosed within the nucleus - found in plants and animals can be as large as 1mm diameter and several cm long

Exocytosis

The process by which vesicles containing proteins fuse with the plasma membrane to release their contents outside the cell.

Structure of mitochondria membrane

Double membrane, highly permeable outer membrane contains many different carrier proteins that transport small charged molecules such as metabolites. Inner membrane is convoluted and highly permeable with cristae folds for increased surface area.

Extracellular matrix (ECM)

A complex network of proteins and carbohydrates outside the cell that provides structural support and regulates cellular functions.

Flagella

Long, whip-like structures that propel cells through their environment via microtubule doublets that slide relative to each other as dynein arms ‘claw’ along the adjacent doublet via ATP

Gap junctions

Cell connections that allow the passage of materials and communication between adjacent cells.

Golgi Apparatus

A complex of flattened sacs involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.

Intermediate Filaments

Fibers of varying diameters that provide structural support and help maintain the integrity of the cell.

Intermediate filaments

Filaments that provide mechanical support to the cell and stabilize the position of organelles.

Light Microscopy

Use of microscopes that utilize glass lenses to illuminate and collect light from an object.

Light Microscopes (LM)

Utilize glass lenses to capture light for imaging, with a resolution limit of about 200 nm.

Lysosomes

Organelles containing acidic hydrolytic enzymes used for digestion and recycling of cellular waste.

Magnification

The process of enlarging an image to make small objects visible.

Magnification

The ratio of image size to actual sample size in microscopy.

Meristematic Cells

Self-renewing plant stem cells divided into one daughter cell that continues to divide and one that differentiates.

Meristems

Regions in plants where rapid cell division occurs, allowing for growth and development.

Microfilaments (Actin filaments)

Thin fibers that play roles in cell movement and shape maintenance.

Microfilaments

The thinnest fibers of the cytoskeleton, composed of two twisted chains of globular actin proteins, involved in cell movement and shape.

Microscope

An instrument that magnifies small objects, allowing detailed observation of cells.

Microtubules

Thick, hollow structures made of globular tubulin protein, important in maintaining cell shape, cell motility, and intracellular transport.

Mitochondria

Organelles that function in cellular respiration, storing energy as ATP, and are believed to have evolved from endosymbiosis.

Mitochondrial matrix

The interior compartment of mitochondria where the citric acid cycle occurs.

Nuclear Envelope

A double lipid bilayer that surrounds the nucleus, enveloping the DNA - continuous with the endoplasmic reticulum.

Nucleolus

The site within the nucleus where ribosomal RNA (rRNA) is synthesized and ribosomal subunits are assembled.

Nucleus

The dominant structure in eukaryotic cells containing DNA encased by a nuclear envelope, evolving from prokaryotic ancestors

Optical Sectioning

A method used in microscopy, like confocal microscopy, to obtain clearer images from dense samples.

Peroxisome

An organelle containing enzymes that detoxify harmful substances and break down fatty acids.

Peroxisomes

Organelles that break down unwanted molecules and contain enzymes to detoxify harmful substances, including breaking down hydrogen peroxide.

Phagocytosis

A process where cells engulf and digest particles or microorganisms.

Photosynthesis

The process by which plants convert sunlight into chemical energy, occurring in thylakoid membrane of chloroplasts.

Physical Sectioning

Techniques for cutting samples into thin slices, often using a microtome, for microscopy.

Plasma Membrane

The boundary that encloses all cells, controlling the movement of substances in and out.

Plasma Membrane

The selectively permeable boundary of the cell, composed of lipids and proteins, regulating the passage of substances.

Plasma membrane

A selectively permeable barrier that surrounds the cell, controlling the passage of substances in and out.

Plasmodesmata

Channels that perforate cell walls in plants, connecting the cytoplasms of adjacent cells for material exchange.

Plant cell walls

Rigid structural layers outside the plasma membrane in plant cells, made of cellulose.

Plastids

A family of organelles in plant cells evolved from endosymbiotic bacteria - has a double membrane the outer of which is from the ancestral cell and inner from bacterium - contains DNA, RNA and small ribosomes.

Primary cilium

A non-motile projection that serves sensory functions in many cells.

Prokaryotic Cells

Cells without internal compartments or membrane-bound organelles, including bacteria, characterized by simple structures and a nucleoid where DNA is located.

Protists

Single-celled eukaryotes.

Resolution

The ability to distinguish two points as separate entities, limited by the capabilities of the microscope and human vision.

Resolution

The minimum distance at which two distinguishable points can be seen as separate entities, influenced by the wavelength of the illuminating light.

Resolution of a Lens

A measure of the minimum distance between two distinguishable objects.

How does protein synthesis occur within ribosomes

Helicase unwinds DNA double helix - RNA polymerase synthesises mRNA by reading DNA 3’-5’ and building complementary mRNA in 5’-3’. Ribosome assembles around mRNA and tRNA carrying amino acids will bind to start codon, as each codon is read an amino acid is added to the polypeptide chain until it reaches a stop codon and the chain is released.

Ribosomes

Cellular structures responsible for protein synthesis, found in both prokaryotic and eukaryotic cells.

Rough Endoplasmic Reticulum (RER)

A type of ER with ribosomes attached to the surface, involved in synthesizing membrane and secretory proteins. Synthesis can be incorporated into membrane or secreted into lumen to be transferred around the cell. When within the lumen, the protein will fold and at times a sugar may be attached to form a glycoprotein in a process called glycosylation.

Scanning Electron Microscope (SEM)

A microscope that scans a beam of electrons across a sample to create a 3D image without sectioning.

Scanning Electron Microscope (SEM)

Electron microscope that scans a beam across the sample, collecting secondary electrons to create an image.

Smooth Endoplasmic Reticulum (SER)

A type of ER without ribosomes, responsible for lipid synthesis and detoxification processes.

Smooth endoplasmic reticulum (SER)

A part of the endoplasmic reticulum that synthesizes lipids and detoxifies drugs.

Tight junctions

Membrane proteins that form seals between adjacent cells, preventing leakage of fluid - allows control of molecules in and out of the cell and tissue.