CELLS
Structure and Functions of Human Cells

Human cells

Basic unit of structure & function

200 different cell types

3 main parts:
1.
Plasma membrane
2.
3.
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:
1.


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
1.
2.
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:
1.
2.
3.
Nuclear envelope
Nucleoli
Chromatin

Multinucleated Muscle Cells
Multinucleated Liver Cells
Anucleated Red Blood
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