Chapter 3- The Cellthexgene.weebly.com/uploads/3/1/3/3/31333379/lec4.pdf · To run the animations...

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Chapter 03

Lecture and

Animation Outline

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Functions

• Basic unit of life

• Synthesis of molecules

• Communication

• Cell metabolism and energy release

• Reproduction and inheritance (DNA)2

Cell Structure

• Organelles:

- specialized structures in cells that perform

specific functions

- Ex. Nucleus, mitochondria, ribosomes, etc.

• Cytoplasm:

jelly-like substance that holds organelles

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4


Microtubule

Peroxisome

Centrioles

Centrosome

Phagocytic

vesicle

Lysosome

fusing with

incoming

phagocytic

vesicle

Lysosome

Nucleus

Nuclear

envelope

Nucleolus

MicrovilliCilia

Secretory

vesicles

Golgi

apparatus

Smooth

endoplasmic

reticulum

Rough

endoplasmic

reticulum

Free

ribosome

Ribosome

Mitochondrion

Cell

membrane

Cytoplasm

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Cell Membrane

• What is it?

outermost component of a cell

• Functions:

- selective barrier

- encloses cytoplasm

• Extracellular: material outside cell

• Intracellular: material inside cell

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Structure of Cell Membrane

• Called Fluid Mosaic Model

• Made of phospholipids and proteins

• Phospholipids form a double layer or bilayer

• Phospholipids contain 2 regions: polar and

nonpolar

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• Polar regions:

- “heads”

- hydrophilic (H2O loving)

- exposed to H2O

• Nonpolar regions:

- “tails”

- hydrophobic (H2O fearing)

- away from H2O

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Figure 2.14b

Figure 3.2a

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Movement through Cell Membrane

• Cell membrane selectively determines what can

pass in and out of the cell.

• Enzymes, glycogen, and potassium are found in

higher concentrations INSIDE the cell.

• Sodium, calcium, and chloride are found in higher

concentrations OUTSIDE the cell.

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Ways molecules Pass through Cell Membrane

1. Directly through (diffusion):

O2 and CO2 (small molecules)

2. Membrane channels:

- proteins that extend from one side of cell

membrane to other

- size, shape, and charge (+/-) determine what can

go through

- Ex. Na+ passes through Na+ channels

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3. Carrier molecules:

- bind to molecules, transport them across, and

drop them off

- Ex. glucose

4. Vesicles:

- can transport a variety of materials

- fuse with cell membrane


Gated Na+

channel

(open)

Gated Na+

channel (closed)

K+ leak

channel

(always open)K+

Na+

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Diffusion• What is it?

movement of molecules from areas of high to low concentration

• Solution:

solid, liquid, or gas that contains one or more solutes

• Solute:

substance added to solvent that dissolves

• Solvent:

substance such as H2O that solute is being added to

Ex. Add salt to H2O. H2O =solvent, salt=solute,

mixture=solution

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• Concentration gradient:

- measures conc. difference at 2 points

- greater the distance the faster the solute

will travel

• Filtration:

movement of fluid through a partition with holes

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Mediated Transport Mechanisms

• Facilitated diffusion:

- diffusion with aid of a carrier molecule

- requires no ATP

• Active transport:

- moves substances from low to high conc.

- requires ATP

- Ex. Sodium-potassium pump


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2

3

4

5

6

1

2

3

4

5

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Na+–K+ pump

Three sodium ions (Na+) and adenosine

triphosphate (ATP) bind to the

sodium–potassium (Na+–K+) pump.

Na+–K+ pump

changes shape

(requires energy).The ATP breaks down to adenosine diphosphate

(ADP) and a phosphate (P) and releases energy.

That energy is used to power the shape change in the

Na+–K+ pump.

The Na+–K+ pump changes shape, and the Na+ are

transported across the membrane and into the

extracellular fluid.

Two potassium ions (K+) bind to the Na+–K+ pump.

The phosphate is released from the Na+–K+ pump

binding site.P

K+

Na+–K+ pump

resumes original

shape.

The Na+–K+ pump changes shape, transporting K+

across the membrane and into the cytoplasm. The

Na+–K+ pump can again bind to Na+ and ATP.

P

ATP

Na+

Na+

K+

ADP

K+Na+

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K+

A Na+–K+ pump maintains a concentration of Na+ that is higher outside

the cell than inside.

Na+ move back into the cell by a carrier molecule that also moves glucose.

The concentration gradient for Na+ provides the energy required to move

glucose, by cotransport, against its concentration gradient.

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1

2

Na+–K+

pump Na+

Carrier

molecule

Glucose

Glucose

Na+

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Osmosis

• What is it?

diffusion of water across a cell membrane

• Osmotic pressure:

force required to prevent movement of water across

cell membrane


*

1 2 3

Because the tube contains salt ions

(green and pink spheres) as well

as water molecules (blue spheres),

there is proportionately less

water in the tube than in the beaker,

which contains only water. The

water molecules diffuse with their

concentration gradient into the

tube (blue arrows). Because the

salt ions cannot leave the

tube, the total fluid volume inside

the tube increases, and fluid moves

up the glass tube (black arrow) as a

result of osmosis.

The solution

stops rising when

the weight of the

water column

prevents further

movement of

water into the

tube by osmosis.

Water moves by osmosis into

the tube until the weight of

the column of water in the

tube (hydrostatic pressure)

prevents further movement

of water into the tube. The

hydrostatic pressure that

prevents net movement of

water into the tube is equal

to the osmotic pressure of

the solution in the tube.

The tube is immersed in

distilled water. Water

moves into the tube by

osmosis (see inset above*).

The concentration of salt in

the tube decreases as

water rises in the tube

(lighter green color ).

Distilled

water

Water

Selectively

permeable

membrane

3% salt solution

Weight

of water

columnSalt solution

rising

Osmosis

The end of a tube

containing a 3% salt

solution (green) is closed

at one end with a

selectively permeable

membrane, which allows

water molecules to pass

through but retains the

salt ions within the tube.

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Types of Osmotic Solutions

• Hypotonic solution:

- lower conc. of solutes outside cell

- higher conc. of H2O outside cell

- H2O moves into cell

- lysis (burst)

• Hypertonic solution:

- higher conc. of solutes outside cell

- higher conc. H2O inside cell

- H2O moves out

- crenation (shrinks)

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• Isotonic solution:

- equal conc. of solutes

- water doesn’t move

- cell remains intact

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Endocytosis• What is it?

process that brings materials into cell using

vesicles

• 2 types

- Phagocytosis:

cell eating (solid particles)

- Pinocytosis:

cell drinking (liquid particles)

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Exocytosis

• What is it?

process that carries materials out of cell

using vesicles

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The vesicle membrane

fuses and the vesicle

separates from the cell

membrane.

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2

3

Receptor

molecules

Molecules to

be transported

Receptor molecules on

the cell surface bind to

molecules to be taken

into the cell.

The receptors and the

bound molecules are

taken in to the cell as a

vesicle is formed.

Cell membrane

Vesicle

2

1

3

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Cell Structures

• Cytoplasm

Location: inside cell

Characteristic: jelly-like fluid

Function: give cell shape and hold organelles in

place

• Nucleus

Location: center of cell

Characteristic: all cells contain nucleus at some

point

Function: houses DNA

• Nuclear envelope:

Location: edge of nucleus

• Nuclear pores:

Location: surface of nucleus

Function: where materials pass in and out of

nucleus

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Figure 3.13a

• Chromosome:

Location: inside nucleus

Characteristic: made of DNA and proteins

Function: part of genetic makeup

• Chromatin:

Location: inside nucleus

Characteristic: loosely coiled chromosomes

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• Nucleolus

Location: in nucleus

Function: produce ribosomes

• Ribosome

Location: attached to RER or cytoplasm

Function: produce proteins

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Ribosomal proteins, produced in the

cytoplasm, are transported through

nuclear pores into the nucleolus.

The small and large ribosomal subunits

leave the nucleolus and the nucleus

through nuclear pores.

rRNA, most of which is produced in the

nucleolus, is assembled with ribosomal

proteins to form small and large ribosomal

subunits.

The small and large subunits, now in the

cytoplasm, combine with each other and

with mRNA during protein synthesis.

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2

3

4

1

2

3

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rRNA

Ribosomal

proteins from

cytoplasm

Small

ribosomal

unit

Large

ribosomal

unit

Nuclear pore

mRNA

Ribosome

Nucleolus

Nucleus

DNA

(chromatin)

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• RER (Rough Endoplasmic Reticulum)

Location: cytoplasm

Characteristic: membranes with ribosomes attached

Function: site of protein synthesis

• SER (Smooth Endoplasmic Reticulum)

Location: cytoplasm

Characteristic: membranes with no ribosomes

Function: site of lipid synthesis (Ex. Cholesterol)

Figure

3.16

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• Golgi apparatus

Location: cytoplasm

Characteristic: closely, packed stacks of

membranes

Function: collect, sort, package, and distribute

proteins and lipids

• Secretory vesicle

Location: cytoplasm

Function: distributes materials out of cell

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• Lysosome

Location: cytoplasm

Function: enzymes that digest foreign material

• Mitochondria

Location: cytoplasm

Characteristic: contains folds (cristae)

Function: produces ATP

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• Cilia

Location: cell surface

Characteristic: many per cell

Function: move materials across cell’s surface

• Flagella


Characteristic: 1 per cell

Function: move cell, Ex. sperm

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• Microvilli


Characteristic: shorter than cilia

Function: increase surface area

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Cytoskeleton

• What is it?

- cell’s framework

- made of proteins

• Functions:

- provide support

- hold organelles in place

- enable cell to change shape

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Types of Cytoskeleton

• Microtubules:

- largest diameter

- provide structural support

- form cilia and flagella

• Intermediate filaments:

- medium diameter

- maintain cell shape

• Microfilaments:

- smallest diameter

- involved in cell movement

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TEM 60,000x

Centriole

(in longitudinal

section)

Centriole

(in cross

section)

(b)

Microtubule

triplet

(a)

(b): © Biology Media/Photo Researchers, Inc.

Whole Cell Activity• A cell’s characteristics are determine by the

type of proteins produced

• Proteins’ function is determined by genetics

• Information in DNA provides the cell with a

code for its cellular processes

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DNA

• What is it?

- double helix in nucleus

- composed of nucleotides

- contains 5 carbon sugar (deoxyribose,

nitrogen base, phosphate

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Flow of Genetic Information

• Also called Central Dogma

• Occurs in three stages:

– DNA replication

– Transcription

– Translation

DNA

Replication

Gene Expression

• What is it?

- information in DNA directs protein

synthesis

- proteins provide code for gene expression

- enzymes regulate chemical reactions

- uses transcription and translation

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Transcription

• What is it?

- process by which DNA is “read”

- occurs in ribosomes

- produces mRNA (messenger RNA)

- mRNA contains codons

- codons: set of 3 nucleotide bases that code for

a particular amino acid

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Translation

• What is it?

- process by mRNA is converted into amino

acids (polypeptides)

- produces proteins

- codons pair with anticodons

- anticodons: 3 nucleotide bases carried by tRNA

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Cell Division

• What is it?

- formation of 2 daughter cells from a single

parent cell

- uses mitosis and meiosis

- each cell (except sperm and egg) contains

46 chromosomes (diploid)

- sperm and egg contain 23 chromosomes

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Mitosis

• What is it?

- cell division that occurs in all cells except

sex cells

- forms 2 daughter cells

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Components of Mitosis

• Chromatid:

2 strands of chromosomes that are genetically

identical

• Centromere:

where 2 chromatids are connected

• Centrioles:

small organelle composed of 9 triplets

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Stages in Mitosis

1. Interphase:

- time between cell divisions

- DNA is in strands (chromatin)

- DNA replication occurs

2. Prophase:

- chromatin condenses into chromosomes

- centrioles move to opposite ends

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3. Metaphase:

chromosomes align

4. Anaphase:

- chromatids separate to form 2 sets of

chromosomes

- chromosomes move towards centrioles

5. Telophase:

- chromosomes disperse

- nuclear envelopes and nucleoli form

- cytoplasm divides to form 2 cells74

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