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Notes Chapter 4 (LS)
4-1 Cell Growth and Division:
Why do cells divide?:
 We grow because cells divide and we are gaining more
cells as we develop/grow
Constant Change:
 Our bodies are changing every second through cell
replication = cell division.
The Cell Cycle:
 You are currently in a rapid growth phase known as
adolescence.
 Cell cycle involves two parts = 1) interphase and 2)
mitosis
A. Interphase. Majority of cell cycle is spent in interphase
3 parts
1. Rapid growth (4 hours) G1
2. Growth and Synthesis of DNA (10 hours)
3. Growth and Preparation for division (4 hours)
 Nerve and muscle cells no longer divide after you are
born, they are in constant interphase.
 Skin cells and other like them are constantly replacing
dead cells = more complex cell cycle.
B. Mitosis: (shortest part of cell cycle) = 2 hours
 Def.. is the process by which cell divides
to form two identical cells
Four steps of Mitosis in an animal cell:
1. Prophase:
 Chromosome can be seen
 Nuclear membrane disappears
 Centrioles move to opposite ends of
cells
 Centrioles move thread like spindle
fibers across cell.
Metaphase:
1. Double stranded chromosomes line up in center of cell.
2. Spindle fibers attach to centromere = center of chromosome.
Anaphase:
 Double chromosome divides at
centromere
 Divided chromos ome strands go to
opposite ends of cell
mary of an interesting point.
You can position the text
box anywhere in the
document. Use the Drawing
Tools tab to change the
Q: Why must the chromosomes separate and move to opposite
formatting of the pull quote
ends of the cell?
text box.]
A:
Telophase:
 Centrioles and spindle fibers start to
disappear
 Chromosomes become harder to see
 Cell has split to form two cells
 Nuclear membrane reappears in both
cells = daughter cells = visible
nucleus
Mitosis in Animal Cells –vs – Mitosis in Plant Cells:
 In an animal cell the membrane cytoplasm pinches
to form new cells
 Rigid cell walls on plant cells do not allow
pinching to take place
 Plate forms instead of pinching and separates two
nucleus
 Plant cells do not have centrioles but do have
spindle fibers
Results of Mitosis:
 Two new nucleus are formed with same number of chromosomes
 Each cell in your body contains 46 chromosomes = 23 pairs
A -sexual reproduction:
A-sexual Reproduction def: new organisms are formed
from parent.
 Offspring of a-sexual reproduction have the exact same DNA as their
parent = cloning.
Types of A-sexual Reproduction:
Animal Cells:
1. Fission: equal splitting of a one celled organism. Ex Bacteria
2. Budding: unequal splitting of one celled organism Ex. Hydra
3. Regeneration: a part of organism is cut from the rest of body and grows
into separate offspring. Ex. Sponges and star fish
Plant Cells:
1. Runners: new plants form from an end of plant like a root under or above
the ground. Ex. Strawberries and grasses.
2. Cuttings: plant re-grows from part that has been cut Ex. Philodendron
3. Sporulation: release of pollen grains in air Ex. dandelions
Section 4-2
Sexual Reproduction:
Sexual Reproduction: def.. new organism forms by two different parents sex
cells.
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

Need a male and a female for sexual reproduction
Male organisms sex cell is called a sperm.
Sperm are smaller than eggs and have tails that allow them to move to egg.
Female organisms sex cell is called an egg.
 Eggs are bigger than sperm and contain food material ex. Yolk
 Sexual reproduction increases a variety of traits in organism =
increase in adaptation and survival.
Production of Sex Cells:
Meiosis: production of sex cells through the process of nuclear
division.
The importance of sex cells:
 Body cells have 23 pairs of chromosomes = total of 46 chromosomes
 Pairs form because chromosomes are alike
 Cells are described as diploid(2n) for having two of the same chromosomes
= pairs of chromosomes
 Sex cells have half this number due to meiosis = 23 total chromosomes
 Sex cells are known to be Haploid(n) = “single form” = single
chromosomes (half the number of chromosomes compared to body cell or
original(parent) cell)
What is the haploid and diploid number for a donkey(see ?
Fertilization:
Fertilization: def… The joining of a sperm and an egg to form a zygote.
 Sperm with 23 chromosomes joins an egg with 23 chromosomes to form a
zygote with 46 chromosomes.

Zygotes cells start to specialize (ears eyes etc) mitosis starts (rapid cell
division)
Figure 4-10
Meiosis:
 Two divisions occur ending with 4 cells with half the number of
chromosomes in a human body cell = 23 chromosomes in a sex cell.
Meiosis I: pairs of chromosomes have now separated = 2 cells with 23 nonpaired chromosomes = haploid.
Phases: see mitotic phase results
1. Prophase I: double stranded chromosome pairs and spindle fibers appear.
2. Metaphase I: chromosome pairs line on center of cell and spindle fibers
attach to centromere.
3. Anaphase I : matching chromosomes separate from each other go to
opposite ends of cell.
4. Telophase I : cytoplasm divides two cells to form
Draw phases from page 106
Meiosis II: (similar to mitosis but chromosomes don’t duplicate to form other
23 chromosomes to form pairs) Two cells divide to form four sex cells with half
the number of chromosomes = 23 chromosomes = haploid.
1. Prophase II : single chromosome double stranded appear and spindle
fibers
2. Metaphase II: single chromosomes align on center of cell and are
connected to spindles fibers
3. Anaphase II: spindle fibers separate single chromosomes at = ½
chromosome # = haploid.
4. Telophase II: cytoplasm divides, spindle fibers disappear nuclear
membrane reappears around chromosomes.
 Result of meiosis is 4 useful sex cells with ½ the number of
chromosomes = 23 haploid chromosomes.
Draw phases from page 107
Section 4-3
DNA……Whats DNA?
DNA: Code in the form of a chemical known as Deoxyribonucleic acid.
 D=Deoxyribose(sugar)
 N=Nucleic
 A=Acid
 DNA(deoxyribonucleic acid) is found in chromosomes that are found in the
nucleus of a cell.
 DNA controls all cell activities
 All cells contain DNA
 Scientists Rosalind Franklin discovered that the DNA molecule was a
strand of molecules in a spiral form = shape of ladder
 Model of DNA was made in 1953 by James Watson and Francis Crick with
the help of Franklin and other scientists
 Watson and Crick model is called the “Double Helix” (AKA twisted
ladder)
Watson and Crick Model:
DNA contains:
 Sides of ladder are made of sugar and
phosphate
 The “rungs” that hold the two sugar
phosphate strands apart are made of
nitrogenous bases
Four Nitrogenous Bases:
1. Adenine = A…….Green
2. Thymine =T……..Blue
3. Guanine = G…….Yellow
4. Cytosine = C…….Red
 Adenine is paired with Thymine
 Guanine is paired with Cytosine
RNA: Ribonucleic acid
 Responsible for making protein directed by DNA
 Contains sugar Ribose
 Uses nitrogen base Uracil instead of Thymine
 RNA is single stranded instead of double stranded like DNA
3 Types of RNA:
1. mRNA: messenger RNA
 brings message for protein building from nucleus to ribosome
2. tRNA: transfer RNA
 brings needed amino acids from cytoplasm to ribosome to build
specific protein
3. rRNA: Ribosomal RNA
 rRNA makes up the ribosome
 reads protein message from mRNA to build protein correctly at
ribosome
Gene: part of DNA that codes for a specific protein
Mutation: permanent change in DNA
Practice Drawing Model :
(can use web site at http://gslc.genetics.utah.edu/units/basics/builddna/ )
Predict the sequence of second strand!