-Cells are about 10 -20 micrometers in size
-Three people from Netherlands Hans Lipphershey , Hans and Zachrias Janssesn (who were
father and son) are given credit for inventing
-Larger species have more cells, NOT BIGGER cells.
-Cell size is the same for whale and humming bird.
-Electron microscopes 1000X more powerful than Light
Overview of Cell Structure
-There are trillions of cells in human body but 200
different types of cells according to structure and
-All muscle cells contain multiple nuclei
(multinucleated), cytosol, ribosomes, and mitochondria
which is common to many cells
- Muscle cells slow -twitch (type 1) and fast twitch (type
-Most cells have major 3 subdivisions such as
(i) plasma membrane: which encloses the cell
(ii) nucleus: which contains the cells genetic material
(iii) cytoplasm: the portion of the cell’s interior not occupied by the nucleus
- plasma membrane: thin membraneous structure which encloses the cell
-Oily and separates ICF(interior cellular fluid) from ECF ( extra -cellular fluid)
-is a barrier, and also helps control the entry of food and other needed supplies and guards
against unwated traffic in and out of the cell.
- Two major parts of cells interior are (i) Nucleus (ii) Cytoplasm
-Nucleaus: contains the genetic information
Structure: contains double layered membrane called nuclear envelope which is peirved by many
nuclear pores which allow traffic to move between nuc leaus and cytoplasm.
- Two main purpose
(i) Directs protein synthesis
(ii)Serves as a genetic blueprint during cell replication
- Cytoplasm: the portion of the cell’s interior not occupied by the nucleus but includes
- Cytoplasm contains membrane enclosed structures called organelles ( little organs) Chapter
-50% of the cell vol is occupied by organelles
- 6 main types of organelles are:
(i) Endoplasmic Reticulum
- Cytosol: the remainder of the cytoplasm not occupied by the organelles consists of the
cytosol (“cell liquid”)
-Cytosol is made up of a semiliquid, gel like mass laced with an elaborate protein network
known as the cytoskeleton.
Intercellular Fluid (ICF) : includes all the fluid contained within the plasma membrane,
including the cytosol, organelles, and the nucleus.
(i) Endoplasmic Reticulum
Structure: Extensive contionsou membranous network of fluid -filled tubules and
flattened sacs partially studded with ribosomes
Function: Forms new cell membrane and other cell
components and manufactures products for secretion
ER is a continuous organelle with many interconnected
The ROUGH ER
- outer surface with dark studded protein -assemblers
(workbenches) called RIBOSOMES due to that it has
-projects out from the smooth ER
-Not permanently attached to ER
-Rough ER works with Go lgi Complex to assemble new
proteins and get them into proper destinations
-Along with Ribosomes also has new proteins which are released in the ER lumen.
The two main purpose of these proteins are
(i) some proteins are destined for export to the cell’ s exterior as secretory products , such as
protein hormones or enzymes ( all enzymes are proteins).
(ii) Other proteins are transported to sites within the cell for use in constructing new cellular
membrane ( plasma or new organelle mem)
Q How do the newly synthesized molecules witin the ER lumen get to their destinations at other
sites inside the cells or to the outside of the cell if they cannot pass out of the ER membrane? Chapter
Ans: They do with action of the smooth Endoplasmic Reticulum ( the transporter)
The SMOOTH ER
-Structure: is smooth no ribosomes, mesh of interconnected tubes.
- Function: serves as a central packaging and discharge site for molecules to be transported
-Newly synthesized proteins go from rough ER to smooth ER . Portion so fht s mooth ER then
bud off forming transport vesicles (which contain many new molecules encolosed in a
spherical membrane derived from the smooth ER. )
vesicle: fluid filled membrane enclosed intra-cellular cargo container
Review page 26 for secretion process for proteins synthesized by ER.
Smooth ER helps in lipid metabolism
-It has enzymes for synthesis of lipids
-In liver cells, smooth ER contains enzymes for detoxifying harmful substances produced witin
the body metabolism or any other substances.
-Muscles have an elaborate but modified smooth ER known as sarcoplasmic reticulum which
-Calcium important for myoosin attachment to the actin which is why there is muscle contraction
-Structure: Sets of stacked, flattened membranous sacs
-Function: Modifies packages and distributes newly synthesized proteins
-Cells which are highly specialized for protein secretion have hundereds of stacks of Golgi.
Lysosomes and Endocytosis
-Cell contains about 300 Lysosomes.
-Structure: Membranous sacs containing hydrolytic enzymes.(Most commonly small about 0.2
-Functions: Serves as digestive system of the cell, destroying foreign substances and cellular
-Small bodies within the cell that breakdown organic m olecules.
-Lysosomes serve as the “intracellular digestive system.”
Endocytosis is a process by which cells absorb molecules (such as proteins) by engulfing them
Endocytosis has three ways:
(i) Phagocytosis ( very few cells)
(iii) Pinocytosis ( most cells)
(iii) Receptor mediated (also some cells) Chapter
Phagocytosis (cell eating)
- Extracellular material which is to be attacked by the Lysosomal enzymes is brought in by
the process of Phagocytosis ( a type of endocytosis)
-large multimolecular particles are internalized
-only a few cells are capable of doing that
-White blood cells are an example and when there is an
bacterium or other particle, it extends its pseudopods (“
false feet”) that completely surround or engulf the particle or
trap it within the vesicle.
-The engulfed material is broken down into amino acids,
glucose, and fatty acids for the cell to use.
Pinocytosis (cell drinking)
-No pseudopods are formed
- In the process of pinocytosis the plasma membrane froms an
-Any substance is found within the area of invagination is brought
into the cell.
-The plasma membrane seals at the surface of the pouch ,
trapping the contents in a small , intracellular endocytotic
-Dynamin: protein molecule responsible for pinching off an
endocytotic vesicle, forms rings that wrap around and writing the neck of the pouch severing the
vesicle from the surface membrane.
Receptor mediated (also some cells)
-Highly selective process that e nables cells to import
specific large molecules from the environment.
-Cholesterol complexes, Vitamin B12, the hormone insulin
and iron are examples of substances taken into cells by this
-HIV, AIDS, also can gain entry via this process Chapter
-Lysosomes can also fuse with aged or damaged organelles to remove these useless parts of
the cell. This selective digestion is known as autophagy “self eating” .
-If they accumulate could cause disease such as Tay-Sachs disease characterized by
abnormal accumulation of complex molecules found in nerve cells.
Peroxisomes and Detoxification
-Several hundred peroxisomes are present
Size is almost /3to ½ of the lysosomes.
Structure: Membranous sacs containing oxidative enzymes
Function: Perform detoxification activities
UNLIKE LYSOSOME THEY DON’T HAVE HYDROLYTIC ENZYMES but they have OXIDATIVE
-Oxidative enzyme: use Oxygen to take out hydrogen from certain molecules which helps
detoxify some wastes in the cell. ( ie alcohol)
-Major product generated in the peroxisomes is hydrogen peroxide (H O ). 2 2
-Catalase: anti-oxidant enzyme which decomposes potent H O in2o 2 O and 2.
Mitochondria and ATP Production
-Cells contain few hundereds to several thousands mitochondria
-Structure: Oval shaped bodies enclosed by two
membranes with the inner mem folded into cristae
that project into interior matrix.
-about 1-10 micrometer
-Descendants of bacteria
-Has its own DNA
-Diseases related to mitochondria include
Nervous-system and muscle diseases such as
Function: Acts as energy organelles, extracts energy from the food , major sites for ATP
production, contains enzymes for ETC and
Kreb(Citric) cycle. Chapter
-Generate about 90% that we need to survive.
-Cristae: contains crucial proteins for converting energy from food to usable form (ETC
-Inner membrane: folds increase the surface area for housing the important proteins. -Matrix:
contains concentrated mix of hundreds of diff dissolved enzymes ( the t ricarboxylic acid cycle
-Source of energy for the body is the chemical energy from the carbon bonds of ingested food.
-But our body cannot use this energy directly and has to be converted into Adenosine-
-ATP is the currency of the body
-ATP is used it makes Adenosine-Diphosphate
-ATP à (Splitting) ADP + Pi + energy for the use by the cell
-ATP is generated in most cells using the following 3 reactions to generate energy
(i) Glycolysis: happens in cytosol(fluid) (also valid answer is cytoplasm(space))
-involves 10 steps
-breaks down simple 6 -carbon sugar molecule into TWO 3-carbon pyruivic molecules.
-Energy from the broken chemical bonds is used to convert ADP to ATP.
-Not that much efficient , only 2 ATP are formed
-Related to McArdle disease ( causes cramp -like pains) when the people cannot break down
glycogen to glucose
-Anaerobic (doesn’t need oxygen)
(ii) Kreb Cycle (Tricarboxylic Acid Cycle)
-occurs in the mitochondria matrix
-Pyruvic acid enters mitochondria matrix via protein monocarboxylate transporter
-Pyruvic acid is catalyzed by the enzyme Pyruvate Dehydrogenase (PDH)
-Pyruvic acid from glycolysis is converted into Acetyla Coa which enters the tricarboxylic acid
cycle also known as the Kreb or Citric cycle.
-This process consists of 8 different biochemical rxns directed by the enzymes of mitochondrial
-It also prepares and generates hydrogen carrier molecules for entry into the ELECTRON
-Acetyl CoA ( 2-C molecule) combines with Oxaloacetic acid (4 -C molecule) to form a (6 -C
molecule) called citric acid which is where the name comes from the Citric acid cycle.
Steps of the process:
1. The citric acid cycle begins when Coenzyme A transfers its 2 -carbon acetyl group to the 4-
carbon compound oxaloacetate to form the 6 -carbon molecule citrate (see Fig. 18).