Cell Structure & Function

Ch.4 & 1-4

(4-1) History

• Cell: smallest unit that can carry on the processes of life

• Hooke (1665): looked at plants under microscope & saw “little boxes”– Named them “cells”

• Leeuwenhoek (1673): 1st to see living cells

Cell Theory

1. All living things are composed of cells

2. Cells are the basic unit of an organism

3. Cells only come from the reproduction of existing cells

(4-2) Intro to Cells

• Cell Diversity– Your body has over 200 different types of

cells

Red Blood Cells Bacterial Cells Skin Cells

Cell Size

• Most cells are microscopic

• Limited by surface area to volume ratio– Larger ratio = more efficient

Surface Area to Volume Ratio

• Surface Area: L x W x # of sides

• Volume: L x W x H

• Ratio: SA / V

Required rate of transportproportional to Volume, V

Feasible rate of transportproportional to Surf ace Area, S

S/V declines with L, meaning that V increases faster than S.

= L= L3

= 6 x L2

Hence, as cells get larger, desired rate increases f aster than f easible rate.

As cell gets larger, V f aster than S

Cell Shape

• Determined by the function of the cell

Basic Parts of a Cell

• Plasma (cell) membrane: covers cell’s surface & provides barrier

• Cytoplasm: fluid (cytosol), cytoskeleton, & organelles inside membrane– Site of chemical rxns

• Nucleus: control center

Basic Cell Types

• “Before nucleus” (nucleoid)

• No membrane organelles

• Single cell organisms

• “True nucleus”

• Membrane organelles

• Multicellular & single cell organisms

Prokaryotic vs. Eukaryotic

Cellular Organization

• Colonies:– Identical cells in a connected group– Not multicellular (few activities coordinated)

• Multicellularity:– Tissue– Organ– Organ system

(4-3) Organelles & Features

• Structures are determined by the functions of each part

Plasma Membrane

• Function: allows substances into & out of the cell

• Selectively permeable: allows only certain things to cross the membrane

Parts of the Membrane

• Membrane lipids– Phospholipid

bilayer: hydrophobic & hydrophilic ends

Parts of the Membrane (cont.)

• Membrane proteins– Peripheral proteins:

attached to sides– Integral proteins:

embedded w/in

Fluid Mosaic Model

• Membrane behaves like a liquid

• Mosaic: changing pattern of proteins & lipids

Nucleus

• Function: store hereditary info

(DNA) & control the cell

• Contains: – nuclear envelope: surrounds nucleus– nuclear pores: holes in envelope that allows

material to enter & leave nucleus– nucleolus: area of concentrated

DNA (chromatin)

Mitochondria

• Function: makes ATP (E)

• “Powerhouse” of the cell

• Has own DNA

Rough Endoplasmic Reticulum (RER)

• Function: makes proteins & phospholipids, & prepares molecules for export out of cell

• Attached ribosomes make “rough”

Smooth ER (SER)

• Function: makes lipids & steroid hormones, metabolizes carbs, regulates Ca2+ levels, & is detoxification center for cell

Ribosomes

• Function: makes proteins

Golgi Apparatus

• Function: stores, sorts, modifies, & ships materials out of the cell

Vesicles

• Lysosomes: break down macromolecules– Release glucose into blood– Break down bacteria

• Peroxisomes: break down fatty acids– Detoxification center in liver cells

Cytoskeleton

• Function: support system of the cell; aid in movement w/in the cell

– Microtubules

– Microfilaments

Cilia & Flagella

• Function: locomotion & movement of materials around the cell

• Animal cells only*

(4-4) Plant Cell Organelles

• Cell Wall

• Central vacuole

• Plastids

Cell Wall

• Function: protects the cell; gives shape & structural support

• Outside cell membrane

• Made of cellulose & proteins

Central Vacuole

• Function: stores materials such as water, enzymes, & waste

• Other vacuoles store toxins

Plastids

• Have their own membrane & DNA & store materials (pigments, starch)

• Chloroplasts: plastids that undergo photosynthesis

(1-4) Microscope

• Instrument that produces an enlarged image of an object

• Magnification: increase of an object’s size

• Resolution: ability to show details clearly

Light Microscopes

• Stage: where slide is placed

• Objective lens: enlarges image

• Ocular lens: magnifies image further

• Nosepiece: revolves lenses

• Power of magnification: factor of enlargement– Obj. x ocular = total power of mag.– Ex: 40X x 10X = 400X

Light Microscope (cont.)

• Diaphragm: adjusts amount of light

• Coarse-adjustment: focuses specimen

• Fine-adjustment: focuses specimen even more

Electron Microscopes

• Beam of e- produces enlarged image of nonliving specimen

• More powerful than light microscopes

• 2 types:– Transmission (TEM)– Scanning (SEM)