Chapter 4Cell Structure and Function

Names of the 17th Century

Leeuwenhoek- skilled lensmaker, looked at protists, bacteria, “small animalcules” in tooth tartar

Hooke- saw compartments in cork, called “cellulae” for small rooms, now termed cell

1800’s

By the 1820s lenses were sharper

Brown- identified plant cell nucleus

Schleiden- wondered how cells develop in plants

Schwann- cells are in animal tissue as well and have an individual life of own

Virchow- every cell comes from a pre-existing cell

Invisible to the naked eye

Hooke’s view

Today’s Microscopes

The Cell Theory

1. Organisms have one or more cells.

2. The cell is the smallest unit of an organism that still displays properties of life.

3. Life arises from growth and division of a single cell.

Cells and Structure

bacteria and archaeans are prokaryotes: simplest cells, no nucleus or membrane bound organelles

eukaryotes have a nucleus and other membrane bound organelles

Properties of Life Displayed

capacity for metabolism

response to the environment

growth and reproduction

all cells differ in size, shape and activity

Structures In All Cells

plasma membrane

DNA

cytoplasm

ribosomes

Plant and Animal Cell

DNA

found in nucleus in eukaryotes, surrounded by a nuclear membrane

found in a nucleoid region in prokaryotes, there is no membrane enclosing this area of the cytoplasm

Cytoplasm

consists of the space between the plasma membrane and the region of DNA

semifluid

suspends organelles to perform tasks such as protein synthesis and energy conversion

cytoplasm

Cell Membrane

defines cell, separates from surroundings, allows certain things through such as H2O, CO2, O2 freely, others need help such as nutrients and ions

lipid bilayer is basis of plasma membrane and other membranes in cell

oily, prevents passage of water soluble sub.

Bilayer Structure

Cell Membrane

membranes inside cell act as channels and sacs to transport, synthesize, modify, store, digest (golgi, ER, vacuole, lysosome)

proteins embedded in lipid bilayer or on surface are responsible for many functions such as acting as channels or pumps for substances to cross, receptors for hormones, and other molecular cell needs

Cell Membrane Mosaic

cytoplasm

lipid bilayer

recognition protein

receptor protein

protein pump

protein channel protein pump

extracellular environment

Cell Size

largest cell is yolk of bird egg, watermelon tissue cells, amphibian and fish eggs

most of volume is nutrients and not much activity

if cell must perform a task, it must be tiny

Cell Size

key is surface area to volume ratio- this keeps the cell from growing too large

volume increases faster than surface area, and then there is not enough surface to get substances in and out fast enough to support the increased volume

cells that cannot support metabolic activity die

Solutions

larger cells can be long and thin, or have many folds in the membrane to increase the surface area (frilly)

muscle cells and nerve cells are long and thin

SA:V

Prokaryotic Cells

smallest cells living in a variety of environments

2 domains: 1. bacteria 2. archaea

similar in size and appearance

differ in AA sequence used to start polypeptide chain (archaea is same as eukaryotes) and protein that helps in folding DNA, called histone

Cell Wall

cell wall outside plasma membrane gives rigidity, shape

usually coated with sticky carbohydrate to help adhere to surfaces (teeth, intestines)

cell wall is permeable

Extracellular Structures

many have flagella, often 1 or more, made of motor like structure (not microtubules as in eukaryotes)

can also have pili, filiments to help cling to surface

special sex pili reels in another cell and trade of genetic material follows

Bacterial Flagella

Inside the Prokaryotes plasma membrane has built in molecules for certain

jobs such as protein channels, transporters, energy conversion

cytoplasm has ribosomes to build proteins

nucleoid region of DNA, one circular piece of DNA called bacterial chromosome

some have plasmids, small circles of DNA with only a

E. Coli DNA

flagellum

pillus

nucleoid

Cyanobacteria

part of membrane folded into cell with pigments and molecules embedded for photosynthesis-- ancestor of chloroplast?

Eukaryotic Cells“true nucleus”

organelles for certain functions with enclosed microenvironment to control substances entering and leaving

mitochondria and chloroplasts hold H ions for generation of ATP

lysosome has enzymes for digestion

Interaction of Organelles

secretory pathway: route for proteins from ribosomes ER golgi plasma membrane release

endocytic pathway: moves molecules into cell- vesicles pinch off of cell membrane to transport a substance

Plant Cell

Animal Cell

The Nucleus

2 main functions: 1. keeps DNA away from cytoplasmic rxns. 2. controls substances going in and out of nucleus

contains nucleolus: site of ribosome construction

at least one

mass of proteins and genes coding for ribosomal RNA

Nuclear Envelope

double lipid bilayer (2 of them)

outer merges with ER, has ribosomes on it

inner has attached proteins that anchor DNA and keep it organized

proteins spanning both layers are receptors, transporters

Nuclear Envelope

DNA

codes for proteins, not visible when cell is not dividing, condense and coil when dividing

nucleoplasm

chromatinnucleolusnuclear envelope

Endomembrane SystemConsists of A. ER B. golgi body C. vesicles

ER: flattened channels folded repeatedly where proteins modified, lipids assembled, vesicles pinch off and deliver to golgi, continuous with nuclear membrane

rough: ribosomes attached

smooth: no ribosomes, makes lipids for cell membrane

Endomembrane System

sarcoplasmic reticulum: type of smooth ER that functions in muscle contraction

golgi bodies: membrane folded on itself and stacked, attaches sugar and lipid side chains to proteins from ER and sends finished product out in a vesicle

Endomembrane System

Membraneous Sacs

exocytic vesicles: release substances to outside cell

endocytic vesicles: bring molecules into cell

lysosomes: bud from golgi, store digestive enzymes, will fuse with another vesicle to activate enzymes

peroxisomes: enzymes to digest fatty acids, amino acids, liver and kidney peroxisomes degrade alcohol

Membraneous Sacs

vacuole: form from fused vesicles, storage

plant central vacuole is large, fluid filled, stores amino acids, sugars, wastes, will expand as fills and force cell wall to expand, 50-90% of cell interior in mature cell

MitochondriaATP formation in aerobic respiration

have own DNA and divide on own, some have ribosomes

outer and inner membranes creates 2 sections

inner membrane is highly folded, H ions flow through and ATP is generated through proteins embedded in membrane

H ions stocked in outer compartment and flow to inner

Mitochondriahigh energy cells have thousands, ex. liver, muscle

inner compartment

outer compartment

inner membrane

outer membrane

Specialized Plant Organelles

plastids: function in storage or photosynthesis

chloroplasts

chromoplasts

amyloplasts

Chloroplastsphotosynthesis takes place here

2 outer membranes

stroma is semifluid inside

third membrane in stroma, highly folded, called thylakoid, forms stacks called grana

photosynthesis takes place in thylakoid where chlorophyll is located

Chloroplasts

ATP, NADPH formed, energy used to build sugars

stroma

thylakoid outer membranes

Chromoplasts

no chlorophyll but carotenoids (reds, yellows) of autumn leaves, fruits, roots, vegetables, attract animals

Amyloplasts

pigment free, store starch

find many in stem, tubers (underground stems, ex. potatoes), seeds

Cell Surface Specializations

Cell wall: wraps around plasma membrane of many protists, fungi, and plants

primary: made of secreted polysaccharide pectin to glue cells together, thin and pliable

secondary: inner surface of primary wall, stronger

Cell Wall

primary

secondary layers

Cell Junctions

structures that allow for cells to communicate or adhere to one another

Animals: 3 types

tight

adhering

gap

Animal Cell Junctions

tight: seals so no fluid leaks between cells, find in stomach, internal cavities, linings of outer surfaces

adhering: link cells that are stretched such as skin, heart, organs that stretch

gap: cytoplasm of cells is directly connected so open channel for movement of fluids such as in heart muscle cell

Animal Cell Junctions

Plant Cell Junction

Plasmodesmata: connect cytoplasm for rapid movement of substances (like gap junction in animals)

Cytoskeleton

structural framework of eukaryotic cells

basis for shape and internal organization

allows organelle movement inside cell

made of protein filaments that are permanent or formed when needed

Microtubules

largest cytoskeletal element that keeps organelles in place or moves them, ex. spindle fibers for chromosome movement in mitosis and meiosis

hollow cylinders of tubulin protein each oriented so “plus” end faces growth direction and “negative” end is anchored in patches of centrosomes, areas of microtubule origin

Microfilaments

thinnest of elements

2 helically coiled chains of actin protein monomers

often in bundles, ex. cell cortex, a bundled mesh reinforcing cell shape and aids in pinching cell in mitosis division

can anchor membrane proteins

Structure of filaments

microtubule microfilament intermediate filament

Accessory Proteins

kinesin and myosin are motor proteins that move with inputs of ATP and can help move cell parts such as a vesicle along a microtubule

Intermediate Filamentsmedium size, found in animal cells only, strengthen

and maintain cell shape and parts

6 known groups

lamins: weaved mesh, reinforces nucleus and anchors actin and myosin filaments to aid in contraction of muscle cells

desmins and vimentins: hold contractile units in place

cytokeratins: reinforce nail, claw, horn, hair cells

Intermediate Filaments

Prokaryotes

no well developed cytoskeleton, but do have reinforcing filaments found in some bacteria, made of protein subunits similar to tubulin and actin, with similar assembly pattern

How Cells Movemotor proteins: microtubules and microfilaments act as

roads for motor proteins to travel, fueled by ATP

kinesin, dynein, myosin

chloroplasts, chromosomes, muscle cell all are moved due to motor proteins

vesicles moved a certain distance before handed off to another motor protein

Motor Protein

vesicle

motor protein

filament

Cilia, Flagella, False Feet

structures that are extensions of the plasma membrane used for movement

cilia are shorter extensions covering some protists, and animal cells such as lung cells

flagella are longer, whip-like

Structure

centrosome: anchors microtubules, gives rise to centriole which gives rise to microtubules organized in a “9 + 2” pattern

centriole acts as base of pattern, called a basal body

9 + 2 Array

9 microtubule pairs form ring around central pair, held in place by protein spokes and linker proteins along length of pairs

Cilia and Flagella

microtubules cannot be pushed further out, so motor proteins create a bending effect around the 9+2 array which bend the cilia or flagella

Pseudopods: False Feet

lobes bulge out of cell to move or engulf prey

microfilaments inside elongate and advance cell by means of motor protein and cell membrane is dragged along with them

amoeba

Cilia

Flagellum

Pseudopods

9 + 2 Array