Carbohydrates: Monosaccharides, Disaccharides & Polysaccharides

Carbohydrates

• Primary energy source for cells, and provide structural support in cell walls.
• Play roles in cell recognition and signaling.
• Composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio
• Monosaccharides are single sugar units used in cellular respiration.
• Disaccharides consist of two monosaccharides joined together.
• Polysaccharides are complex carbohydrates made of many sugar units.
• Glycoproteins and glycolipids in cell membranes facilitate cell communication and immune responses.

Monosaccharides

• Include glucose, fructose, and galactose.

Disaccharides

• Include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

Polysaccharides

• Starch stores energy in plants and is made of α-glucose.
• Glycogen stores energy in animals and has a highly branched structure for quick energy release.
• Cellulose forms plant cell walls and provides rigidity, made of β-glucose.
• Chitin is found in fungal cell walls and arthropod exoskeletons, similar to cellulose but contains nitrogen.

Lipids

• Function in long-term energy storage and is the main component of biological membranes.
• Act as signaling molecules and provide insulation and protection
• Triglycerides consist of glycerol and three fatty acids.
• Saturated triglycerides have single bonds and are solid at room temperature, found in animals.
• Unsaturated triglycerides have double bonds and are liquid at room temperature, found in plants.
• Phospholipids include glycerol, two fatty acids, and a phosphate group, forming the cell membrane with an amphipathic nature.
• Steroids have four fused rings, including cholesterol and hormones

Steroids

• Cholesterol maintains membrane fluidity
• Hormones include testosterone and estrogen.

Waxes

• Provide waterproofing

Membranes and Cells

• Phospholipid bilayer forms the cell membrane.
• It controls transport and communication.
• Cholesterol modulates membrane fluidity and stability.

Proteins

• Essential for structural support, act as enzymes, and regulate various body functions.
• Built from amino acids linked by peptide bonds and contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
• The primary structure is the sequence of amino acids, determined by DNA.
• Secondary structures include α-helices and β-pleated sheets, stabilized by hydrogen bonds.
• Tertiary structure is the 3D shape formed by interactions between R groups.
• Quaternary structure arises from multiple polypeptide chains interacting.

Protein Functions

• Enzymes speed up biochemical reactions.
• Structural proteins provide support.
• Transport proteins move substances.
• Defensive proteins are involved in the immune response.
• Signaling proteins include hormones.
• Motor proteins facilitate movement.

Protein Connections

• Membrane proteins act as transporters, receptors, and enzymes.
• Enzymes regulate metabolic pathways within organelles.

Membranes and Membrane Transport

• The plasma membrane regulates the movement of substances into and out of cells.

Membrane structure

• Phospholipid bilayer has hydrophobic tails and hydrophilic heads, making it amphipathic
• Integral proteins are embedded in the membrane
• Peripheral proteins are on the membrane surface.
• Cholesterol maintains fluidity and stability.
• Carbohydrates such as glycoproteins and glycolipids aid in cell recognition.

Passive transport

• Does not require ATP
• Simple diffusion involves the movement of small, nonpolar molecules across the membrane.
• Facilitated diffusion uses transport proteins to help polar or large molecules cross the membrane.
• Osmosis is the movement of water across a semipermeable membrane.

Active Transport

• Requires ATP
• Protein pumps move ions against their concentration gradient.
• Endocytosis involves taking in large molecules via vesicles.
• Phagocytosis and pinocytosis are types of endocytosis.
• Exocytosis involves vesicles fusing with the membrane to release substances.

Organelles and Compartmentalization

• Cells are organized into compartments to increase efficiency.
• The nucleus stores DNA, controls cell activities, and is the site of transcription.
• Ribosomes synthesize proteins.
• Free ribosomes make cytoplasmic proteins.
• ER-bound ribosomes make secretory proteins.

Endoplasmic Reticulum (ER)

• Rough ER is involved in protein synthesis and transport.
• Smooth ER is involved in lipid synthesis and detoxification.
• The Golgi apparatus modifies, sorts, and packages proteins and lipids.
• Mitochondria produce ATP via cellular respiration.
• Lysosomes break down waste and cellular debris.
• Peroxisomes detoxify substances and break down fatty acids.
• Chloroplasts (in plants) carry out photosynthesis.
• Vacuoles store water and nutrients.
• The cytoskeleton provides structural support and facilitates intracellular transport.

Compartmentalization

• Increases efficiency by isolating processes and allows specialization within organelles.
• Protects the cell from harmful reactions.

Cell Specialization

• Different cells have specialized functions based on their structure and organelles.
• Epithelial cells line surfaces, protect, and secrete substances.
• Muscle cells contract for movement via actin and myosin.
• Nerve cells (neurons) transmit electrical signals via axons and synapses.
• Red blood cells (erythrocytes) carry oxygen and lack a nucleus to maximize hemoglobin content.
• White blood cells (leukocytes) are involved in the immune response and engulf pathogens.
• Sperm and egg cells carry genetic information for reproduction.
• Xylem transports water and is reinforced with lignin.
• Phloem transports sugars via sieve tube elements and companion cells.

Organelles

• Muscle and sperm cells have more mitochondria for energy.
• Cells producing proteins have more rough ER.
• Plant cells have large vacuoles for water storage.