Introduction to Cells

Animal Cells, Plant Cells, Bacterial Cells, Oh My!

Relative Size of Cells

Relative Size of Cells

• It is all relative...

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Fig. 7.5

• Metabolic requirements set an upper limit to the size of a single cell.

• As a cell increases in size its volume increases faster than its surface area.– Smaller objects have a greater

ratio of surface area to volume.

• All cells are surrounded by a plasma membrane.

• The semifluid substance within the membrane is the cytosol or cytoplasm, containing the organelles.

• All cells contain chromosomes which have genes in the form of DNA.

• All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes.

All cells have…

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• A major difference between prokaryotic and eukaryotic cells is the location of chromosomes.

• In an eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the nucleus.

• In a prokaryotic cell, the DNA is NOT surrounded by a nuclear envelope.

• Prokaryotic cells do not have membrane bound organelles, such as the Golgi apparatus and the endoplasmic reticulum.

Major Differences

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

Prokaryotic Cell

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Animal Cell

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Plant Cell

Similarities and Differences?

• Break into pairs and create a chart to begin noting similarities and differences among the three types of cells we just reviewed.

Introduction to Organelles

• Not these…

• The plasma membrane functions as a selective barrier that allows passage of oxygen, nutrients, and wastes for the whole volume of the cell.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.6

Plasma Membrane

Cytoskeleton• The cytoskeleton is a network of fibers

extending throughout the cytoplasm.• The cytoskeleton

organizes the structures and activities of the cell.

• The cytoskeleton also plays a major role in cell motility.

– Cilia (lungs)– Flagella (sperm)

What life would be like without a cytoskeleton…

Nucleus•Surrounded by Nuclear envelope

•Same structure as cell membrane•DNA•Chromatin

•DNA + histones (proteins)•Chromosomes

•Unique number based on species•Nucleolus

•Cluster of RNA and proteins•Helps to make ribosomes

Structure of DNA in your nucleus

Ribosomes• Ribosomes contain rRNA and protein.• A ribosome is composed of two subunits that

combine to carry out protein synthesis.• Some ribosomes, free ribosomes, are

suspended in the cytoplasm and synthesize proteins that function within the cell.

Rough Endoplasmic Reticulum

• The endoplasmic reticulum (ER) accounts for half the membranes in a eukaryotic cell.

• The ER membrane is continuous with the nuclear envelope.

• Rough means there are Ribosomes attached to the outside of the ER– Makes proteins to be exported out of the

cell

• There are two, albeit connected, regions of ER that differ in structure and function.– Smooth ER looks

smooth because it lacks ribosomes.

– Rough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.11

Endomembrane System

Smooth ER• The smooth ER is rich in enzymes and plays a

role in a variety of metabolic processes.• Enzymes of smooth ER synthesize lipids,

including oils, phospholipids, and steroids.• The smooth ER also catalyzes a key step in the

mobilization of glucose from stored glycogen in the liver.

• Other enzymes in the smooth ER of the liver help detoxify drugs and poisons.

Golgi apparatus• Many transport vesicles from the ER travel to

the Golgi apparatus for modification of their contents.

• The Golgi is a center of manufacturing, warehousing, sorting, and shipping.

Mitochondria• Mitochondria is the organelle that

converts energy to forms that cells can use for work- “powerhouse”.

• Mitochondria are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen.

• Has small quantities of DNA that help make own proteins.– The DNA is passed on from mother to child-

maternity testing possible.

Mitochondria

Chloroplast• Chloroplasts, found in plants and

eukaryotic algae, are the site of photosynthesis.– They convert solar energy to chemical

energy and synthesize new organic compounds from CO2 and H2O.

• Contains chlorophyll, which causes the green color of many plants.

• Has small quantities of DNA that help make own proteins.

Chloroplast

Various Vesicles• The lysosome is a membrane-bounded

sac of hydrolytic enzymes that digests macromolecules.– Food vacuoles, from phagocytosis, fuse

with lysosomes.

• Contractile vacuoles, found in freshwater protists, pump excess water out of the cell.

• Central vacuoles are found in many mature plant cells.