Structure and Functions of Human Cells

Human cells Basic unit of structure & function 200 different cell types 3 main parts: Plasma membrane Cytoplasm Nucleus

Cell diversity

Cell Structure

Cytoplasm Between plasma membrane & nucleus Three elements: Cytosol: fluid Eg. water, proteins, salts, sugars Organelles: specific functions Inclusions: chemical substances that vary depending on cell type Eg. glycogen (liver), lipid droplets (fat cells), melanin (skin & hair)

Organelles “little organs” Specialized compartments  specific functions Membranous = membrane-bound Mitochondria, peroxisomes, lysosomes, ER, Golgi apparatus Nonmembranous = no membrane cytoskeleton, centrioles, ribosomes

Cell Organelles Ribosomes: Make proteins. Rough Endoplasmic Reticulum (Rough ER): Make proteins. Smooth Endoplasmic Reticulum (Smooth ER): Make lipids. Golgi Apparatus: Molecules are packaged and transported. Mitochondria: Power center. (ATP) Lysosomes: Contain digestive enzymes. Microfilaments and microtubules: cell structure and transport (cytoskeleton) Cilia and flagella: Increase surface to volume ratio for absorption and helps with locomotion.

Plasma membrane Function: enclose cell contents, control exchange of substances with environment, cell communication Made of: Lipid bilayer-Phospholipids Cholesterol Glycolipids Proteins

Fluid mosaic model Proteins float in fluid lipid bilayer

Membrane lipids: Phospholipid: Polar/hydrophilic (water-loving) “head” Nonpolar/hydrophobic (water-fearing) “tail”

Lipid bilayer

Semipermeable Membrane Very small molecules (like water) can flow freely through the membrane. Large molecules can only get in or out by using a protein “door”. Very small molecules that are polar must also use a protein.

2 Types of Transport Passive Transport: No energy required. With the concentration gradient. Active Transport: Energy being used to move something into the cell. Against the gradient.

Passive Transport Diffusion: Molecules moving from an area of high concentration to low concentration. Osmosis: The diffusion of water across a semipermeable membrane.

Osmosis can damage cells… Hypertonic (Water leaves cell.) Isotonic (Balanced.) Hypotonic (Water enters cell.) Very Hypotonic (Water enters, cell bursts.)

Diffusion Solutes moving from an area of high concentration to an area of low concentration.

Diffusion Solutes moving from an area of high concentration to an area of low concentration.

Diffusion Solutes moving from an area of high concentration to an area of low concentration.

Diffusion Solutes moving from an area of high concentration to an area of low concentration.

Diffusion Solutes moving from an area of high concentration to an area of low concentration.

Diffusion, cont. Small molecules diffuse faster than large molecules. Increasing the temperature causes diffusion to occur more quickly.

Facilitated Diffusion Molecules moving across the membrane with the assistance of a carrier protein but requiring no energy. This is passive transport because it requires no energy!

2 Types of Transport Passive Transport: No energy required. With the concentration gradient. Active Transport: Energy being used to move something into the cell. Against the gradient.

Active Transport Moving solutes against a concentration gradient.

Active Transport, cont. Carrier Proteins: Proteins in the membrane of the cell that bring out or take out large molecules. Bulk Movement: Transporting large molecules (such as polysaccharides or proteins) across the cell membrane.

Bulk Movement Exocytosis: Transporting out of the cell. Endocytosis: Transporting into the cell. Pinocytosis: Cell drinking. Phagocytosis: Cell eating.

Endomembrane system System of organelles that work to Produce, store, export biological molecules Degrade harmful substances Nuclear envelope, rough ER, smooth ER, Golgi apparatus, secretory vesicles, lysosomes

Endomembrane system

Nucleus

Nucleus Control center  contains DNA Most cells have only 1 nucleus Multinucleate: many nuclei (muscle, some liver cells) Anucleate: no nucleus (mature RBC) Three main structures: Nuclear envelope Nucleoli Chromatin

Multinucleated Muscle Cells Anucleated Red Blood Cells Multinucleated Liver Cells

Nuclear envelope Double membrane barrier surrounds nucleus Outer part continuous with Rough ER Nuclear pores: control entry/exit of molecules

Nucleolus (nucleoli) Dark-staining bodies in nucleus 1-2 per cell Site where ribosomes are made

chromatin Chromatin = DNA + Proteins Nucleosome = DNA wrapped around 8 histone proteins Histones allow for compact and orderly packing of long DNA molecules

During cell division, chromatin condenses to form chromosomes.

replication Make identical copies of DNA before a cell divides

Mitosis Part of cell division Replicated DNA divided into 2 daughter cells Usually lasts about an hour Interphase  prophase  metaphase  anaphase  telophase & cytokinesis

DNA = blueprint for protein synthesis Gene: segment of DNA that codes for 1 polypeptide Exon: part of DNA that codes for polypeptides Intron: part of DNA that is noncoding (not “junk”!)

Information Flow: DNA  RNA  proteins

Protein synthesis Transcription: RNA formed from DNA Occurs in nucleus Types: mRNA, tRNA, rRNA Translation: protein synthesis polypeptide formed from mRNA Occurs in cytoplasm By ribosomes