Chapter 3: Cells

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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

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