Download Cells and DNA

Cells, DNA, and You
Basic Cell Structures
• Cells come in many shapes and sizes.
• Despite differences in cell size and shape,
certain structures are common to most cells.
• Cell membrane– the thin, flexible barrier
around the cell.
• Cell wall- found only in plant cells, it is a
strong layer around the cell membrane.
• Some cells have a nucleus which is a large
structure that contains the cell’s genetic
material and controls the cell’s activities.
• The jelly-like material inside the cell
membrane– but not including the nucleus– is
called the cytoplasm.
• The cytoplasm contains many important
structures.
• Biologists divide cells into 2 categories:
eukaryotes and prokaryotes.
• Eukaryotic cells have a nucleus.
• They also contain specialized structures
called organelles.
• Prokaryotic cells do not have a nucleus.
• They are simple being composed of only a
cell membrane and cytoplasm.
Prokaryotic v. Eukaryotic
• All plant, animal, and fungi are eukaryotes, as
well as many microorganisms.
• All bacteria are prokaryotes.
• Even though they are relatively simple,
prokaryotes carry out every activity associated
with life.
• They grow, reproduce, and respond to
changes in the environment.
Nucleus
• The nucleus is the large structure which
controls most cell processes and contains the
hereditary information of DNA.
• DNA holds the coded instructions for making
proteins and other important molecules.
• The nucleus directs the making of proteins,
one of the main functions of cells.
• Nucleolus– small, dense region within the
nucleus where ribosome assembly begins.
• Ribosomes aid in the production of proteins
within the cell.
• One of the most important jobs carried out in
the cell is making proteins.
• Ribosomes– small particles made of RNA and
proteins on which proteins are assembled.
• Nuclear envelope– double membrane that
surrounds the nucleus.
• The envelope has pores which allows
materials to pass in and out of the nucleus.
• The granular material visible within the
nucleus is called chromatin.
• Chromatin consists of fine strands of DNA
bound to protein.
• When a cell divides, chromatin condenses to
form chromosomes, which are rod-shaped
structures that contain the genetic
information to be passed on.
Nucleic Acids
• Nucleic acids are macromolecules containing
hydrogen, oxygen, nitrogen, carbon, and
phosphorus.
• Nucleic acids are polymers assembled from
individual monomers known as nucleotides.
• The nucleotide is made of 3 parts: a sugar
group, a phosphate group, and a nitrogenous
base.
• Individual nucleotides join together to form a
nucleic acid.
• Nucleic acids store and transmit genetic
information.
• There are 2 kinds of nucleic acids: ribonucleic
acid (RNA) and deoxyribonucleic acid (DNA).
DNA
• DNA is what enables cells to have so many
different forms and perform so many different
functions.
• In simple terms, DNA controls the production
of proteins within the cell.
• These proteins in turn form the structural
units of cells and control all chemical
processes within the cell.
• Every new cell that develops in your body
needs an exact copy of the DNA from the
parent cell.
• Additionally, humans and all other organisms
must be able to pass copies of their DNA on to
their offspring in order to continue the
species.
• The structure of the DNA molecule is related
to its 2 primary functions– to store and use
information to direct the activities of the cell
and to copy itself exactly for new cells that
are created.
• The DNA molecule consists of 2 long strands,
each of which is a chain of nucleotide
monomers.
• Each nucleotide has 3 parts:
1. a 5 carbon sugar molecule called
deoxyribose
2. a phosphate group
3. a nitrogenous base
• While the sugar molecule and phosphate
group are the same in every nucleotide, the
nitrogenous base may be any one of four
different kinds.
• The 4 types of nitrogenous bases in DNA are
adenine, guanine, thymine, and cytosine.
• Study the structure of each base in the picture
on the following slide.
• Adenine and guanine belong to a class of
organic molecules called purines which have
a double ring of carbon and nitrogen atoms.
• Thymine and cytosine are pyrimidines and
have a single ring of carbon and nitrogen
atoms.
• Each nucleotide– deoxyribose, phosphate,
and nitrogenous base– bonds to other
nucleotides to form a long strand.
• Two of these strands bonded together form a
molecule of DNA.
• The 2 strands twist around a central axis to
form a spiral structure called a double helix.
• The double helix was first described in 1953
by James Watson and Francis Crick.
• Their discovery was one of the most significant
of the 20th century.
• The DNA molecule looks something like a
twisted ladder.
• The sides of the ladder are formed by
alternating sugar and phosphate units, and
the rungs consist of bonded pairs of nitrogen
bases.
• The rungs of the DNA ladder are always of
uniform length because in each case one base
is a double-ringed purine and the other is a
single-ringed pyrimidine
• The two strands of DNA are held together by
hydrogen bonds between the bases.
• A hydrogen bond is a type of weak chemical
bond that occurs between hydrogen atoms
and more electronegative atoms like oxygen,
nitrogen, and fluorine.
Cell Cultures
• Scientists may take a single cell or a few cells
from the same tissue and place them into a
dish containing a nutrient solution.
• The cell is able to reproduce so that a group
of cells, called a cell culture, develops from
the original cell or cells.
• Cell culture typically refers to the removal of
cells from an animal or plant and their
subsequent growth in a favorable artificial
environment.
• The cells may be removed from the tissue
directly and then separated using enzymes or
mechanical means.
• The cells may also be derived from a cell line
or cell strain that has already been
established.