BIOLOGY MODULE 1

CELLS AS THE BASIS OF LIFE

The Cell

The smallest structural and functional unit of an organism.

Cell Theory

All living things are made of cells, the cell is the smallest unit of life and cells only arise from preexisting cells.

Prokaryotic Cells

• Lack a nucleus and membrane bound organelles

• Small (0.1-5µm)

• DNA exists in a large loop (bacterial chromosome) and small rings called plasmids.

• Examples - Bacteria and Archaea

Eukaryotic Cells

• Contains a nucleus and specialised membrane bound organelles

• Larger (10-100µm)

• Can be unicellular or multicellular; reproduce both sexually and asexually.

• Kingdoms - Protista, Fungi, Plantae and Animalia

Nucleus

The control centre; stores DNA in strands called chromosomes.

Nucleolus

Found inside the nucleus; its primary function is to manufacture RNA, which is then used by DNA to produce proteins.

Ribosomes

Sites of protein synthesis; can be free-floating or attached to the Endoplasmic Reticulum.

Mitochondria

The site of cellular respiration, converting glucose into ATP (energy). They have a double membrane with a highly folded inner layer to increase surface area.

Endoplasmic Reticulum (ER)

Network of membranes. Rough ER has ribosomes and synthesises proteins; smooth ER lacks ribosomes and synthesises lipids.

Golgi Apparatus

Sorts, stores and dispatches cell products.

Chloroplasts

Site of photosynthesis in plants/protists; contains the green pigment chlorophyll.

Vacuoles

Liquid-filled storage for enzymes and nutrients. Large/permanent in plants (provides support); small/temporary in animals.

Cell Wall

A rigid outer layer providing strength. Made of cellulose (plants) or (chitin) fungi.

Lyosomes

Often called the "cell recycling units," these are specialized vesicles that digest unwanted matter and broken-down cell parts.

Plastids

A broader class of organelles found in plant cells that either store nutrients or contain pigment; chloroplasts are the most well-known type of plastid.

Cytoskeleton

A network of protein microtubules and filaments that extends throughout the cytoplasm. It provides the framework for the cell's shape, helps organelles stay in place, and assists in the transport of vesicles.

Centrioles

Small, cylindrical structures made of microtubules. They are crucial for cell division (forming the spindle that holds chromosomes) and are involved in forming cilia and flagella. (Note: Most plant cells do not have these).

Pili

Thin, hair-like protein tubes on the outside of many bacteria

Cilia

Hair-like extensions of the cell membrane used for movement. Are short, numerous, and move in a "beating" motion

Flagella

Hair-like extensions of the cell membrane used for movement. Are longer and move with a "whipping" motion.

Microscopes Formula

Total magnification = (magnification of ocular lens) x (magnification of objective lens)

Light Microscopes

Used for general view

• Advantage - allow for the observation of living specimens.

• Advantage - allow for the observation of colour.

• Disadvantage - has low resolution which is insufficient for viewing tiny cell components like ribosomes.

• Disadvantage - limited magnification which is insufficient for viewing the detailed structure of organelles.

Electron Microscopes

Provide high detail ultrastructure

• Advantage - superior resolution which is sufficient for viewing tiny cell components like ribosomes.

• Advantage - massive magnification (up to 1mil x), making it possible to observe proteins, lipids and even atoms.

• Disadvantage - do not allow for the observation of living specimens.

• Disadvantage - do not allow for the observation of colour.

The Fluid Mosaic Model

Demonstrates the membrane as selectively permeable, controlling what enters/leaves the cell.

Structure: Phospholipid Bilayer

• Phosphate heads - hydrophilic (water loving), facing outwards

• Lipid tails - hydrophobic (water fearing), facing inwards

Components

• Cholesterol - maintains stability and fluidity

• Proteins - integral (span the membrane) or peripheral (on the surface); used for transport and cell signalling.

• Carbohydrates - attached to proteins (glycoproteins) or lipids (glycolipids) for cell recognition.

Passive Transport

Movement along a concentration gradient (high-low); requires no energy.

• Diffusion - spreading of particles until equilibrium is reached

• Osmosis - the diffusion of water through a semi-permeable membrane

• Facilitated diffusion - uses carrier proteins to help large or charged molecules cross.

Active Transport

Movement against a concentration gradient (low-high); requires energy (ATP) and carrier proteins.

Endocytosis

Engulfing large particles by wrapping the cell membrane around them to form a vesicle.

• Phagocytosis - “cell eating” (solids)

• Pinocytosis - “cell drinking” (liquids

Exocytosis

Transporting waste or products out of the cell via vesicles that fuse with the membrane.

SA:V Ratio

• Crucial for efficiency. As a cell grows, its volume increases faster than its surface area, causing the SA:V to shrink.

• Crucial rule - the smaller the cell, the higher the SA:V, allowing for faster exchange of nutrients and waste. This is why cells are microscopic.

Cell Requirements

• Organic substances - glucose, amino acids, lipids and nucleotides.

• Inorganic substances - water, oxygen, carbon dioxide and mineral ions (eg. sodium, chloride)

• Autotrophs - produce their own nutrients (eg. plants via photosynthesis)

• Heterotrophs - obtain nutrients from other organisms

Photosynthesis

Carbon dioxide + water → glucose + oxygen

• Light dependent stages - occurs in the grana (thylakoids); light splits water into hydrogen and oxygen.

• Light independent stage (dark phase) - occurs in the stroma; hydrogen and CO2 combine to make glucose.

Cellular Respiration

Glucose + oxygen → carbon dioxide + water + energy (ATP)

• Aerobic - requires oxygen; produces 36 ATP

• Anaerobic - occurs without oxygen; produces only 2 ATP. (eg. alcohol fermentation | yeast/plants or Lactic acid fermentation | animals)

Enzymes + Models

Are biological catalysts, usually a protein, that speed up chemical reactions in the body. Enzymes only work on one specific substrate because of the shape of their active site.

• Function - speed up metabolic reactions by lowering activation energy.

• Structure - proteins with a specific active site that matches a substrate.

Models

• Lock and key - the active site is rigid and perfectly matches the substrate.

• Induced fit - the enzyme changes shape slightly to fit the substrate more tightly.

Factors Affecting Enzyme Activity

• Temperature - activity increases with heat up to an optimum (37 in humans). Excessive heat causes denaturation (permanent change in shape).

• pH - each enzyme has an optimum pH (eg. pepsin in the stomach works in high acids). Extremes cause denaturation.

• Substrate concentration - rate increases until the saturation point is reached (all active sites are occupied).

Enzyme Inhibition

• Competitive inhibitors - block the active site

• Non-competitive inhibitors - bind elsewhere (allosteric site) and change the enzyme’s shape