INTRODUCTION TO THE STUDY OF CELL AND MOLECULAR

1

CHAPTER 1

INTRODUCTION TO THE STUDY OF CELL AND MOLECULAR

BIOLOGY

OBJECTIVES

• Identify the three tenets of cell theory.• Explain the importance of the fundamental properties shared by all cells.• Compare the structures and functions of prokaryotic and eukaryotic cells.• Distinguish the structures and functions of viruses and viroids.• Differentiate a colony of individual single-celled organisms from a multicellular organism.• Describe how tissue engineering can create cell-based replacement organs.

LECTURE OUTLINE

(1.1) The Discovery of Cells

• Cell and molecular biology is reductionist, based on the view that knowledge of the parts of the whole can

explain the character of the whole.

• The reductionist view can lead to replacement of the wonder and mystery of life by the need to explain

everything in terms of the workings of the "machinery" of living systems which many consider a loss.

• It is hoped that one can replace this loss by an equally strong appreciation for the beauty and complexity

of the mechanisms underlying cellular activity.

Microscopy

• Cell biology began as a result of the discovery that curved glass surfaces can bend light and form images.
• Spectacles were first made in Europe in the 13

th century.

• First compound (double-lensed) microscopes were made by the end of the 16

th century, microscopes provide a magnified image of a tiny object.

• By the mid-1600s, a handful of scientists had used handmade microscopes to uncover a previously

unseen world that could not be seen with the naked eye.

II. Robert Hooke (1665), English microscopist who at age 27 became curator of the Royal Society, England's foremost scientific academy, is generally credited with the discovery of cells.

• In describing the chambers in cork, part of the bark of trees, he called them cells (cellulae) since they

reminded him of cells occupied by monks living in a monastery.

• Found them while trying to explain why cork stoppers could hold air in a bottle so effectively; cork

is part of the bark of trees.Karp's Cell and Molecular Biology, 9e Gerald Karp, Janet Iwasa, Wallace Marshall Solution Manual, For Complete File, Download link at the end of this file 1 / 4

2

• He said "“I took a good clear piece of cork, ….., I cut a piece of it off, and . . . then examining it

with a Microscope, me thought I could perceive it to appear a little porous . . . much like a Honeycomb.”

• He called the pores cells.
• Was looking at the empty cell walls of dead plant tissue that had no internal structure, the walls

originally made by the living cells they surrounded.

III. Anton van Leeuwenhoek (1665-1675) was Dutch seller of clothes and buttons and in his spare time he ground lenses and made simple microscopes of remarkable quality.

• For 50 years, he sent letters to the Royal Society of London describing his microscopic observations,

and included in his letters a rambling discourse on his daily habits and the state of his health.

• He was the first to describe living single cells, and his results were checked and confirmed by Hooke.
• Saw “animalcules” in pond water darting back and forth, the first to do this, using the scopes that he

made.

• First to describe various forms of bacteria from tooth scrapings and water in which pepper was soaked.
• His initial letters to the Royal Society describing what he saw were met with skepticism so the Society

sent its curator, Robert Hooke, to confirm the observations.

• Hooke confirmed Leeuwenhoek's findings and soon Leeuwenhoek was a worldwide celebrity.
• He was visited in Holland by Peter the Great of Russia and the queen of England.

Cell Theory

• The 1830s is when the full and widespread importance of cells was realized.
• Matthias Schleiden, German lawyer turned botanist (1838) concluded that, despite differences in various

tissue structures, all plant tissues were made of cells and that plant embryos arise from single cell.

• Theodor Schwann, German zoologist (1839) and colleague of Schleiden's, realized the cellular basis of

animal life and concluded that plants and animals are similar structures.

• Published a comprehensive report on the cellular basis of animal life.
• Schwann concluded that the cells of plants and animals are similar structures and then proposed the first

two tenets of the cell theory.

• All organisms are composed of one or more cells.
• The cell is the structural unit of life for all organisms.
• However, the Schleiden-Schwann view of cell origin was less insightful, as both agreed that cells could

arise from noncellular materials that was eventually disproved by others; however, it took time due to their prominence.

• It took a number of years before observations by other biologists were accepted to demonstrate that

cells did not arise in this manner any more than organisms arose by spontaneous generation.

• Rudolf Virchow, a German pathologist (1855), made good case for and added third tenet of Cell Theory

derived from his cell division observations that ran counter to Schleiden-Schwann view of cell origins.

• Cells can arise only by division from a preexisting cell.
• Since the discovery of DNA as the genetic material, a fourth tenet of cell theory is sometimes added.
• Cells contain genetic information in the form of DNA, and that information is passed from parent to

daughter cell.

• / 4

3

(1.2) Basic Properties of Cells

• Life is the most basic property of cells, and they are the smallest units to exhibit this property.
• Unlike the parts of a cell, which deteriorate if isolated, whole cells can be removed from a plant or

animal and cultured in a lab where they will grow and reproduce for extended periods of time.

• If mistreated, they may die.
• Death can be considered one of the most basic properties of life, as only a living entity can die.
• Cells within the body generally die by their own hand, by an internal program that causes cells that

are no longer needed or cells that pose a risk of becoming cancerous to eliminate themselves.

• George and Martha Gey, Johns Hopkins Univ. (1951) developed the first human cell culture, HeLa cells,

donated by Henrietta Lacks from her malignant tumor.

• Descendants from this sample are still grown in labs today.
• Descended by cell division from this first cell sample.
• Cultured cells are simpler to study than cells in body, and cells grown in vitro (in culture, outside the

body) have become an essential tool of cell and molecular biologists.

• Much of what we know about cells has been obtained using cells grown in lab cultures.

Cells Are Highly Complex and Organized

• Complexity is evident when encountered, but hard to describe, so think of complexity in terms of order and

consistency.

• If a structure is more complex, a greater number of parts must be in the proper place and there must be

less tolerance of errors in the nature and interaction of its parts.

• Also, more regulation or control must be exerted to maintain the system.
• Cell activities can be remarkably precise, as DNA duplication has error rate <1 mistake every

10,000,000 nucleotides incorporated, and most errors quickly fixed by elaborate repair mechanism that recognizes defect.

• Each level of structure in cells has a great level of consistency from cell-to-cell, and each cell type has a

consistent appearance in EM; its organelles have a particular shape and location in all individuals of species.

• Organelles have consistent macromolecular composition arranged in a predictable pattern.
• Epithelial cells that line the intestine are tightly connected to each other like bricks in wall.
• Cell apical ends (face intestinal lumen) have long processes (microvilli) that facilitate nutrient

absorption.

• Microvilli project outward from apical surface because they contain internal skeleton made of

filaments composed of protein (actin) monomers polymerized in characteristic array.

• At basal ends, intestinal cells have many mitochondria that provide energy to fuel membrane

transport.

• Each mitochondrion is composed of defined pattern of internal membranes, which, in turn, are made

of consistent array of proteins, including the electrically-powered protein that makes ATP.

• Cells achieve organization at many different levels using physical processes that are essentially random.
• Even though living cells are highly complex and ordered, it is evident that random, stochastic events

play a critical role in all cellular activities. 3 / 4

4

• Many molecules in living cells are in constant state of random movement, propelled by thermal energy

from environment, and cells have evolved capacity to utilize this movement in highly directed ways.

• Proteins are complex molecules made of up to hundreds of amino acids and >100,000 Daltons.
• Despite this huge size, they consist of polypeptide chain that has to fold into precisely defined 3D

(native) structure, and if it fails to fold properly, the protein will lack meaningful function.

• Cyrus Levinthal (Columbia U., 1969) identified certain features of folding process that became known

as Levinthal's paradox.

• He noted that, if protein folding depended solely on random molecular movements, it would require

more time than the age of the universe for a protein to fold into its native structure.

• Paradox is that despite their enormous complexity, proteins actually acquire their native structures in

fractions of a second.

• Protein folding driven by random thermal motion, but in stepwise fashion so that protein folds along

pathways in which less formed intermediates guide formation of better-formed later intermediates.

• Folding pathway allows proteins to rapidly "jump" from one step to next until native structure

reached.

• They depend on random activities, but lead to directed outcomes because they select for intermediate

stages that lie on the path leading to the desired outcome.

• Evolution has moved rather slowly at the levels of biological organization with which cell and molecular

biologists are concerned.

• Humans and cats are very different anatomically, but the cells that make up their tissues and their cell

organelles are very similar.

• Actin filaments and the enzyme that makes ATP are virtually identical to similar structures found in

such diverse organisms as humans, snails, yeast and redwood trees.

• Information obtained from studying cells of one organism often has a direct application to other forms

of life.

• Many of the most basic processes (protein synthesis, conservation of chemical energy, membrane

structure, etc.) are remarkably similar in all living organisms.

Cells Possess a Genetic Program and the Means to Use It

• Encoded in collection of genes made of DNA and organisms are built according to the information encoded

therein.

• The human genetic program has enough information, if converted to words, to fill millions of pages of text.
• This vast amount of information is packaged into a set of chromosomes that occupies the space in cell

nucleus, hundreds of times smaller than the dot on an i.

• Genes are more than a storage locker for information, they are the blueprint for constructing cellular

structures, the directions for running cellular activities and the program for making more of themselves.

• Gene molecular structure allows for changes in genetic information (mutations) that lead to variation

among individuals and forms the basis of biological evolution.

Cells Are Capable of Producing More of Themselves

• Cells are capable of producing more of themselves through mitosis and meiosis.
• / 4