Lecture 2 thecellularleveloforganization

CHAPTER 2
The Cellular Level of Organization
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

The purpose of the chapter is to:
1. Introduce the parts of a cell
2. Discuss the importance of the plasma
membrane
3. Discuss the components of the cytoplasm
4. Compare and contrast mitosis and meiosis
5. Understand the effects aging has on the cell
Introduction

3 divisions of a cellstructure:
1. plasma membrane 2. cytoplasm 3. nucleus
A. PLASMA MEMBRANE
- boundary between theoutsideand insideenvironments
•selectively permeable/ semi-permeable
•regulates flow of materials intoand outof thecell
•also provides communication among and between cells and their
external environment
•made up of lipids andproteins
•fluidity – movement of bilayer; self-seals during injury;changes
position in the bilayer(but not flip-flopping); cholesterol
component provides strength at normal body temperature;
becomes fluid at low temperatures

PROKARYOTIC CELL
-A type of cell that lacks a membrane bounded nucleusand the DNA is not
physically separated from the rest of the cytoplasm. The DNA is usually
coiled, attached to the plasma membrane and concentrated in a region of
the cell called theNUCLEOID.
-Are usually very small (less than 5 u in length) with relatively simple
internal structureand are mostlysurrounded bya relativelystiff cell wall.
Ex. bacteria (KingdomMonera)
EUKARYOTIC CELL
-A Cell containing distinct membrane bounded nucleus aswell
as variety of membranous organelles that lend structural and
functional organization to the cellinterior

The cell can be subdivided into 3 parts:




1. Plasma (cell) membrane
2. Cytoplasm
Cytosol
Organelles
1. Nucleus
Chromosomes
Genes
Parts of a Cell

Parts of a Cell

The plasma membrane is a flexible yet
sturdy barrier that surrounds and contains
the cytoplasm of the cell
The Plasma Membrane

Two types of membrane proteins are
 Integral (also called transmembrane) proteins
 Peripheral proteins
Membrane Proteins

 Membrane proteins
can serve a variety of
functions
 The different proteins
help determine many
of the functions of
the cell membrane
Functions of Membrane Proteins

Membranes are fluid structures because
most of the membrane lipids and many of
the membrane proteins move easily in the
bilayer
 Membrane lipids and proteins are mobile in their
own half of the bilayer
Cholesterol serves to stabilize the
membrane and reduce membrane fluidity
Membrane Fluidity

Plasma membranes are selectively
permeable
 The lipid bilayer is always permeable to small,
nonpolar, uncharged molecules
 Transmembrane proteins that act as channels or
transporters increase the permeability of the
membrane
 Macromolecules are only able to pass through the
plasma membrane by vesicular transport
Membrane Permeability

A concentration gradient is the difference in
the concentration of a chemical between
one side of the plasma membrane and the
other
An electrical gradient is the difference in
concentration of ions between one side of
the plasma membrane and the other
Together, these gradients make up an
electrochemical gradient
Gradients Across the Plasma
Membrane

Transport processes that move substances
across the cell membrane are:
 Passive processes



Simple diffusion
Facilitated diffusion
Osmosis
 Active processes


Active transport
Vesicular transport
Transport Across the Plasma
Membrane

Passive Processes

Diffusion is influenced
by:
1. Steepness of the
concentration gradient
2. Temperature
3. Mass of diffusion
substance
4. Surface area
5. Diffusion distance
Simple Diffusion

Transmembrane proteins help solutes that
are too polar or too highly charged move
through the lipid bilayer
The processes involved are:
 Channel mediated facilitated diffusion
 Carrier mediated facilitated diffusion
Facilitated Diffusion

Channel Mediated Facilitated
Diffusion

Carrier Mediated Facilitated Diffusion

Diffusion: A Comparison

The net movement of a solvent through a
selectively permeable membrane from an area
of high concentration to an area of low
concentration
Osmosis

Tonicity of a solution relates to how the
solution influences the shape of body cells
Tonicity

Active Processes

Energy derived from ATP changes the shape of a
transporter protein which pumps a substance
across a plasma membrane against its
concentration gradient
Primary Active Transport

Energy stored (in a hydrogen or sodium
concentration gradient) is used to drive other
substances against their own concentration
gradients
Secondary Active Transport

Active Transport
in Vesicles:
Receptor-
mediated
Endocytosis

Active Transport in Vesicles:
Phagocytosis

Active Transport in Vesicles: Bulk
Phase Endocytosis (Pinocytosis)

Exocytosis – membrane-enclosed secretory
vesicles fuse with the plasma membrane
and release their contents into the
extracellular fluid
Transcytosis – a combination of endocytosis
and exocytosis used to move substances
from one side of a cell, across it, and out the
other side
Active Transport in Vesicles:
Exocytosis & Transcytosis

A Comparison of Transport Types

Parts of a Cell: Cytoplasm

Cytosol is also known as the intracellular
fluid portion of the cytoplasm
Organelles are the specialized structures
that have specific shapes and perform
specific functions
Cytoplasm

Cytoskeleton

Centrosome/Centrioles

Cilia and Flagella

Ribosomes

Endoplasmic Reticulum

Golgi Complex

Lysosomes

Peroxisomes are structures that are similar
in shape to lysosomes, but are smaller and
contain enzymes that use oxygen to oxidize
(break down) organic substances
Peroxisomes

Proteasomes are barrel-shaped structures
that destroy unneeded, damaged, or faulty
proteins by cutting long proteins into smaller
peptides
Proteasomes

Mitochondria

Nucleus

The nucleus contains
the cell’s hereditary
units, called genes,
which are arranged in
chromosomes
Nucleus

Gene Expression

Protein Synthesis
The Protein-making Process

• Proteins are composed of amino acids – there are 20
different amino acids
• Different proteins are made by combining these 20
amino acids in different combinations

• Proteins are manufactured (made) by the ribosomes

•Function of proteins:
1. Help fight disease
2. Build new body tissue
3. Enzymes used for digestion and other chemical
reactions are proteins
(Enzymes speed up the rate of a reaction)
4. Component of all cell membranes

MAKING PROTEINS
Step 1: Transcription

Making a Protein—Transcription
• First Step: Copying of genetic information from DNA to RNA
called Transcription
Why? DNA has the genetic code for the protein that needs to be
made, but proteins are made by the ribosomes—ribosomes are
outside the nucleus in the cytoplasm.
DNA is too large to leave the nucleus (double stranded), but RNA
can leave the nucleus (single stranded).

• Part of DNA temporarily unzips and is used as a
template to assemble complementary nucleotides
into messenger RNA (mRNA).

• mRNA then goes through the pores of the nucleus with
the DNA code and attaches to the ribosome.

MAKING PROTEINS
Step 2: Translation

Making a Protein—Translation
• Second Step: Decoding of mRNA into a protein is called
Translation.
• Transfer RNA (tRNA) carries amino acids from the
cytoplasm to the ribosome.

These amino acids come from the food we eat. Proteins
we eat are broken down into individual amino acids and
then simply rearranged into new proteins according to the
needs and directions of our DNA.

•A series of three adjacent bases
in an mRNA molecule codes for
a specific amino acid—called a
codon.
•Each tRNA has 3 nucleotides
that are complementary to the
codon in mRNA.
•Each tRNA codes for a different
amino acid.
Amino acid
Anticodon

• mRNA carrying the DNA instructions and tRNA carrying
amino acids meet in the ribosomes.

• Amino acids are joined together to make a protein.
Polypeptide = Protein

Use one of the codon charts on the next page to find the amino acid
sequence coded for by the following mRNA strands.
CAC/CCA/UGG/UGA
___________/___________/___________/____________
AUG/AAC/GAC/UAA
___________/___________/___________/____________

Transcription occurs
in the nucleus and is
the process by which
genetic information
encoded in DNA is
copied onto a strand
of RNA to direct
protein synthesis
Protein Synthesis:
Transcription

Translation occurs in the nucleus and is the
process of reading the mRNA nucleotide
sequence to determine the amino acid
sequence of the newly formed protein
Protein Synthesis: Translation

Protein Synthesis During Transcription

Cell division is a process by which cells
reproduce themselves
 Cell cycle
Cell Division

G1phase
S
G2phase
Interphase

During prophase chromatin condenses into
chromosomes
Mitotic Phase: Prophase

During metaphase centromeres of
chromosomes line up at the metaphase
plate
Mitotic Phase: Metaphase

During anaphase centromeres of
chromosomes split and sister chromatids
move toward opposite poles of the cell
Mitotic Phase: Anaphase

During telophase the
mitotic spindle
dissolves,
chromosomes regain
their chromatin
appearance, and a
new nuclear
membrane forms
Mitotic Phase: Telophase

During cytokinesis
a cleavage furrow
forms and
eventually the
cytoplasm of the
parent cell fully
splits
 When this is
complete,
interphase begins
Cytokinesis

3 possible destinies:
1. Remain alive and functioning without dividing
2. Grow and divide
3. Die
Control of Cell Destiny

Reproductive Cell Division: Meiosis I

Reproductive Cell Division: Meiosis II

Cellular Diversity

As we age:
 Our cells gradually deteriorate in their ability
function normally and in their ability to respond to
environmental stresses
 The numbers of our body cells decreases
 We lose the integrity of the extracellular
components of our tissues
Free radicals
Aging and Cells

Lecture 2 thecellularleveloforganization

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