3-1

Functions of the Cell

• Basic unit of life

• Protection and support

• Movement

• Communication

• Cell metabolism and energy release

• Inheritance

3-2

Cell Characteristics

• Plasma Membrane– Outer cell boundary– Substances inside the cell membrane

are intracellular– Substances outside the cell are

extracellular.– Encloses an supports the cell

contents.

3-3

Plasma Membrane

– It attaches cells to the extracellular environment or to other cells.

– The ability of cells to recognize and communicate with each other take place through the plasma membrane

– It determines what moves into and out of cells.

3-4

Plasma Membrane

• Ion movement by cells results in a charge difference across the plasma membrane called the MEMBRANE POTENTIAL

• The outside of the plasma membrane is positively charged compared to the inside because there are more positively charged ions immediately on the outside of the plasma membrane and more negatively charged ions inside.

3-5

Plasma Membrane

• The membrane potential allows cells to function like tiny batteries with a positive and negative pole.

• It is an important feature of a living cell’s normal function.

3-6

Plasma Membrane• Consists of:

– 45% -50% lipids– 45% - 50% proteins– 4% - 8% carbohydrates

• The carbohydrates combine with lipids to form glycolipids

• The proteins combine with lipids to form glycoproteins.

3-7

Membrane Lipids• 1st: Phosoplipids

• Form lipid bilayer

– Double layer of lipid molecules

– They have a polar head (exposed to water inside and outside the cells) and a non polar tail (face one another in the interior of the plasma membrane.

3-8

Membrane Lipids• 2nd: Cholesterol

– Interspersed among the phospholipids and accounts for about 1/3 of the total lipids in the plasma membrane.

– The amount of cholesterol in a given membrane is a major factor in determining the fluid nature of the membrane. Which is critical to its function.

3-9

Membrane Lipids

• Phospholipids form a lipid bilayer

– Hydrophilic (water-loving) polar heads

– Hydrophobic (water-fearing) nonpolar heads

• Cholesterol: Determines fluid nature of membrane

3-10

Membrane Proteins• Many functions of the plasma membrane

are determined by its proteins.

– FLUID-MOSAIC MODEL:

• The plasma membrane is neither rigid nor static in structure.

• It is highly flexible and can change its shape and composition through time.

3-11

Membrane Proteins• Integral or intrinsic

– Extend from one surface to the other

• Peripheral or extrinsic

– Attached to either the inner or outer surfaces of the lipid bilayer

3-12

Marker Molecules

• Allow cells to identify one another or other molecules

3-13

Channel Proteins• Nongated ion channels

– Always open• Ligand gated ion channel

– Open in response to small molecules that bind to proteins or glycoproteins

• Voltage-gated ion channel– Open when there is a

change in charge across the plasma membrane

3-14

Movement through the Plasma Membrane

• Diffusion• Osmosis• Filtration• Mediated transport mechanisms

– Facilitated diffusion– Active transport– Secondary active transport

3-15

Osmosis• Diffusion of water (solvent) across a

selectively permeable membrane• Important because large volume changes

caused by water movement disrupt normal cell function

• Cell shrinkage or swelling– Isotonic: cell neither shrinks nor swells– Hypertonic: cell shrinks (crenation)– Hypotonic: cell swells (lysis)

3-16

Osmosis

3-17

Filtration• Works like a sieve• Depends on pressure difference on

either side of partition• Moves from side of greater pressure

to lower–Example: In kidneys in urine

formation

3-18

Mediated Transport Mechanisms• Many essential molecules, such as amino acids

and glucose, cannot enter the cell by simple diffusion.

• Many products such as proteins cannot exit the cell by diffusion.

• Mediated transport mechanisms involve carrier proteins within the plasma membrane that move large, water-soluble molecules across the membrane.

3-19

Mediated Transport Mechanisms• Involve carrier proteins• Characteristics

– Specificity• To a single type of

molecule– Competition– Saturation

• Rate of transport limited to number of available carrier proteins

3-20

Mediated Transport Mechanisms• Facilitated diffusion

– Higher to lower concentration without metabolic energy

• Active transport– Requires ATP

• Secondary active transport– Ions or molecules move

in same (symport) or different direction (antiport)

3-21

Endocytosis

• Internalization of substances by formation of a vesicle

• Types– Phagocytosis

– Pinocytosis

– Receptor-mediated endocytosis

3-22

Pinocytosis

3-23

Exocytosis

• Accumulated vesicle secretions expelled from cell• Examples

– Secretion of digestive enzymes by pancreas– Secretion of mucus by salivary glands– Secretion of mild by mammary glands

3-24

Cell Characteristics

• Cytoplasm

–Cytosol

–Cytoskeleton

–Cytoplasmic inclusions

3-25

Cytoplasm• Cellular material outside

nucleus but inside plasma membrane

• Cytosol: Fluid portion• Cytoskeleton: Supports the

cell– Microtubules– Microfilaments– Intermediate filaments

• Cytoplasmic inclusions

3-26

Organelles

• Small specialized structures for particular functions

• Most have membranes that separates interior of organelles from cytoplasm

• Related to specific structure and function of the cell

3-27

Centrioles• In specialized zone

near nucleus: Centrosome

• Each unit consists of microtubules

• Before cell division, centrioles divide, move to ends of cell and become spindle fibers

3-28

Cilia• Appendages projecting

from cell surfaces• Capable of movement• Moves materials over

the cell surface

3-29

Flagella• Similar to cilia

but longer

• Usually only one exists per cell

• Move the cell itself in wavelike fashion

• Example: Sperm cell

3-30

Microvilli• Extension of plasma

membrane• Increase the cell

surface• Normally many on

each cell• One tenth to one

twentieth size of cilia

• Do not move

3-31

Ribosomes• Sites of protein

synthesis

• Composed of a large and small subunit

• Types

– Free

– Attached to endoplasmic reticulum

3-32

Endoplasmic Reticulum

• Types– Rough

• Attached ribosomes• Proteins produced

and modified– Smooth

• Not attached ribosomes

• Manufacture lipids• Cisternae: Interior spaces

isolated from rest of cytoplasm

3-33

Golgi Apparatus • Modification, packaging, distribution of proteins and lipids for secretion or internal use

• Flattened membrane sacs stacked on each other

3-34

Peroxisomes and Proteasomes• Peroxisomes

– Smaller than lysosomes

– Contain enzymes to break down fatty and amino acids

– Hydrogen peroxide is a by-product of breakdown

• Proteasomes

– Consist of large protein complexes

– Include several enzymes that break down and recycle proteins in cell

3-35

Mitochondria• Provide energy for

cell

• Major site of ATP synthesis

• Membranes

– Cristae: Infoldings of inner membrane

– Matrix: Substance located in space formed by inner membrane

3-36

Nucleus

• DNA dispersed throughout• Consists of :

– Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out

– Chromatin: Condenses to form chromosomes during cell division

– Nucleolus: Assembly site of large and small ribosomal units

3-37

Chromosome Structure

3-38

Overview of Cell Metabolism

3-39

Overview of Protein Synthesis

3-40

Overview of Protein Synthesis • Transcription

– Copies DNA to form mRNA

– tRNA carries amino acids to ribosome

• Translation

– Synthesis of a protein at ribosome

3-41

Translation

3-42

Cell Life Cycle • Interphase

– Phase between cell divisions

• Mitosis

– Prophase

– Metaphase

– Anaphase

– Telophase

• Cytokinesis

– Division of cell cytoplasm

3-43

Mitosis

3-44

Mitosis

3-45

Meiosis

3-46

Cellular Aspects of Aging

• Cellular clock• Death genes• DNA damage• Free radicals• Mitochondrial damage