Cell Structure and Function

Basic Structure of Cells

Cells are small - 1 to100 micrometers in diameter

Cells exchange nutrients and wastes with their surrounding environments by diffusion

Diffusion is the movement of molecules from areas of high concentration to areas of low concentration

This relatively slow process requires that no part of the cell be to far from the surrounding environment (thus the cells can’t be too big)

All cells bounded by a cell or plasma membrane

Flexible phospholipid bilayer with embedded proteins

All cells have cytoplasm- all the structures that lie inside of the cell membrane but not region that contains the DNA

All Cells use DNA as the blueprint and RNA to copy and implement the blueprint

All Cells obtain energy and nutrients from their environment

Plasma Membrane

Phospholipid bilayer

Proteins imbedded into membrane

ion channels

receptors for chemical messengers

enzymes

Carbohydrate chains - glycolipids and

glycoproteins - outside

Function in cell-to-cell recognition

Fluid mosaic model

Plasma Membrane

Cell Membranes

Barriers to diffusion of molecules

Diffusion - movement of molecules from areas of high conc to areas of low conc

Selectively permeable

O₂ & CO₂ - lipid soluble

Water through pores or channels

Ions through channels

Others molecules and ions may use a carrier

Osmosis

Diffusion of water across a cell membrane

Protein Carriers

Large solute molecules cross membranes via carriers

Facilitated transport

No energy input required

Sugars - amino acids

Active transport

Sugar absorption from the gut

Movement up a conc gradient - requires energy (ATP)

Active Transport

Endocytosis and Exocytosis

Nucleus

Contains DNA - chromatin

Bounded by nuclear envelope

Nuclear pore

Nucleolus- rRNA

Endoplasmic Reticulum

Extensive intracellular membrane system

Rough endoplasmic reticulum

Granular appearance - ribosomes

Smooth endoplasmic reticulum

No ribosomes

Smooth Endoplasmic Reticulum

Site of synthesis - new fatty acids & steroids

In muscle - stores &releases Ca⁺⁺ - for contraction

Detoxification in some cells - e.g. liver

Rough Endoplasmic Reticulum

Site of synthesis of proteins destined to be inserted into plasma membranes or secreted

Ribosomes

Nucleolus is the site of ribosome assembly

Mix of RNA and protein

Ribosomes are the site of protein synthesis

Chains - polysomes

Golgi Apparatus (Body)

Flattened membranous sacs

Modifies proteins for export

Applies destination labels to the proteins

From ER to Golgi

Lysosomes

Formed by golgi

Contains digestive or hydrolytic enzymes

Encapsulates damaged organelles & engulfed foreign objects (endocytosis)

WBCs

Auto digestion during development

Mitochondrion

Powerhouse of thecell

Double membrane

Outer smooth

Inner folded - cristae (folds)

Contain enzymes involved in oxidative metabolism

Chloroplasts & Other Plastids

Specialized for photosynthesis & storage

Chloroplasts

Double membrane

Stroma - semifluid interior

Thylakoid membrane

Disc shaped structures -grana - interconnected

First stage of photosynthesis occurs here

Chlorophylls - light trapping green pigments

Chloroplast Movements

Chloroplasts & other Plastids

Chromoplasts

Abundance of carotenoids

Yellow to red colors seen in the fall

Color in carrots &fruit

Amyloplasts

Storage

Starch grains

Abundant in stems &seeds

Cytoskeleton

Structural elements

Microtubules (tubulin)

Intermediate filaments

Microfilaments

e.g. actin - in microvilli - cause movement

Cilia and Flagella

Make cells move

Hairlike projections -move in undulating fashion

Cilia

Propels one celled organisms about like paramecium

Apical surface - respiratory tract lining

Flagella - whiplike

Propels sperm toward the egg

Microvilli

Apical surface of cells specialized for rapid diffusion

Tiny fingerlike projections

Dramatically increases surface area