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Chapter 3
The Cell: Its Role in Reproducing Life and Producing Variation
Two types of organisms
One cell (Prokaryote)
Many cells (Eukaryote)
Two types of cells
Body cells (Somatic)
Reproductive cells (Gamete)
A Few Interesting Facts About Cells
Every single cell knows exactly what to do from the moment of conception to your death
Cells do everything for you
feel pleasure
form thoughts
extract nutrients from food
distribute energy
carry off wastes
Each of us has only a few hundred different types of cells
Cells come in all different shapes and sizes
A human egg cell is 85,000 times bigger than a sperm cell
On average, a human cell is 20 microns wide, (micron = 1000th of a millimeter)
My thumbnail = 16mm wide or 800 cells across)
Some cells are alive, some dead
All skin cells are dead
We each have about 5 lbs of dead skin cells on us at any one time
Most cells live only a month or so
Liver cells live for years
Brain cells live for our entire lives
We each get 100 billion at birth, never gain any new ones
We lose 500 brain cells per hour
Those that remain are constantly renewing
Our bodies are entirely replaced every nine years
The DNA Molecule: The Genetic Code
Nuclear DNA
Contained within the nucleus of a cell
Makes up chromosomes
Complete set called genome
Mitochondrial DNA
Contained in organelles in cell’s cytoplasm
Inherited from the mother
Can be traced back 100,000s of thousands of years
A few interesting facts about DNA
Six feet of DNA inside every cell
Each strand has 3.2 billion letters of coding
An adult human has 10,000 trillion cells x 6’ DNA = a LOT of DNA
DNA is not living, but it is chemically inert
This is why it can be recovered from ancient bones
White blood cells contain DNA, red blood cells do not
97% of DNA doesn’t do ANYTHING
Only here and there is a length that does anything, and those are the “genes”
Interesting thoughts about DNA
Gene that controls development of mouse eye put into fruit fly larva, makes a fruit fly eye
60% of human DNA can be inserted into fruit flies, 90% in a mouse
June 2, 1999 Using laser beams like tweezers, Japanese Graduate student Yasuharu Arai
managed to tie incredibly tiny knots in strands of DNA.
The DNA in your bone cells is exactly like the DNA in your skin cells, which is exactly like
the DNA in your hair cells, etc…..
The DNA Molecule: The Genetic Code
DNA: The blueprint of life
Chemical template for every aspect of organisms
Double helix, ladderlike structure
Ladder forms nucleotide
Ladder base made up of 4 types
Adenine, thymine, guanine, cytosine
Complementary pairs (A&T, C&G)
The DNA Molecule: Replicating the Code
One function of the DNA molecule is replication.
Part of cell division—meiosis or mitosis
DNA makes identical copies of itself.
Chromosome types
Occur in homologous (matching) pairs
One in each pair from each parent
Autosomes (non-sex chromosomes)
Sex chromosomes
X, Y
Females carry only X chromosomes
Males have one X and one Y chromosome.
The father determines the sex of the offspring.
Mitosis: Production of Identical Somatic Cells
DNA replication followed by one cell division
Diploid cell (contains full set of chromosomes)
Meiosis: Production of Gametes (Sex Cells)
One DNA replication followed by two cell divisions
Gametes are haploid (half the number of chromosomes).
Does not result in identical cell copies
Errors can occur during meiosis.
Producing Proteins: The Other Function of DNA
Proteins are chemicals that make up tissues.
Also regulate functions, repair, and growth of tissues
Proteins are made up of 20 types of amino acids.
11 produced by human body
9 (essential amino acids) come from food we eat
Structural proteins responsible for physical characteristics
Regulatory proteins responsible for functions: enzymes, hormones, antibodies
Protein synthesis involves two steps.
Transcription (unzipping, template for RNA) inside nucleus
Translation (template attaches to ribosomes) outside nucleus
(This is how DNA information gets outside nucleus
DNA in protein synthesis is coding DNA (5%).
Most of human DNA is noncoding (95%).
Genes: Structural and Regulatory
Structural genes are responsible for body structures.
Regulatory genes turn other genes on and off.
Hair growth, limb growth, tooth development, and more