Download Understanding DNA

Differentiation
All the cells in your body have the same
DNA
The fertilized egg (zygote) that made you
divided many times
Cell differentiation- starting stem cells
changed into all the different cell types you
have by turning on certain genes in your DNA
Stem cells- the cells in early development
that have the potential to become any type
of cell
Differentiation Video
STEM CELL
All types of cells
stem from these
cells early in
development of
Babies.
3 Types of Cell Division
1. Binary fission -cell division in
prokaryotes
 2. Cell Cycle (with Mitosis) -cell division
in eukaryotes
 3. Meiosis—cell division to form sex
cells (egg and sperm)

Prokaryotes Cell Division
 Unicellular
so divide by
binary fission
Circular DNA
Results in two cells
genetically the same
What has to take place
before ANY cells divide?
Reasons for Eukaryote Cell
Division

Cell division in multicellular organisms
results in:
– Growth
– Repair or replacement of somatic (body) cells.
– Control of size so nutrients can get in and
waste can get out in a timely fashion
Reasons for Eukaryote Cell
Division
Some cells die quickly and need to be
replaced a lot (skin cells)
 Some cells never get replaced (nerve
cells)
 Some organisms can regenerate whole
body parts

Eukaryotic cells goes
through a series of phases
throughout their life
 The cell cycle-all events
between one cell division and
the next

– It is **ONE REPLICATION
& ONE DIVISION
– Result? 2 daughter cells
genetically exact to the
parent cell they came from

2 basic parts of the cell
cycle:
-1.Interphase- the
longest part of cell
cycle composed of G1,
S, G2 stages
-2.M= Mitosis = Nuclear
division

G1 phase- 1st step of Interphase in the cell
cycle
– G1 (G=gap)
– Cell going through intense growth using lots of food
and energy
– DNA at this point is unwound and called chromatin

S phase -2nd step of Interphase in the cell
cycle
– S=Synthesis phase
– All DNA replicated during this phase so new DNA
being synthesized cell has double the genetic
material
– Sister chromatid- one of two identical parts of a
replicated chromosome

G2 phase- 3rd step of Interphase in
the cell cycle
– G=gap
– Cell grows some more
– Extra organelles are being made

M phase- part of cell cycle after
Interphase (G1, S, and G2) in which
nuclear division occurs
– M=Mitosis = Nuclear division
– MITOSIS IS ONLY THE DIVISION OF THE
NUCLEUS DURING THE CELL CYCLE!!!
– There are four mitotic steps:
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase of Mitosis

DNA coils up into
visible
chromosomes

Nuclear envelope
disappears

Spindle fiber
forms from the
centrioles
Metaphase of Mitosis
Chromosomes
begin to line up
at the equator of
the cell
 Spindle fibers
attach to the
centromere of
each sister
chromatid of the
chromosome

Anaphase of Mitosis
Spindle fibers
begin to pull
apart sister
chromatids. Each
is now a
chromosome
 Spindle breaks
down after this

Telophase of Mitosis
Each side now
has a full set of
chromosomes
 Nuclear envelope
will reform

Cytokinesis

“Cytokinesis”—division of
cytoplasm at the end of
the cell cycle which
cleaves the cell in half
– Animal cells form a “furrow”
– Plant cells form a new cell
wall
– Formation of two, identical
daughter cells
Overall Cell Cycle Process
Interphase (G1, S, G2) and Mitosis (Prophase,
Metaphase, Anaphase, Telophase) IPMAT
 Cell Cycle Animation

Regulation of Cell Cycle
Cyclins- Proteins that control
cell division
 Cancer cells don’t respond to
the cyclin signals--uncontrolled growth (tumors)

 Benign tumors stay intact
 Malignant tumors spread
throughout body (metastasize)

DNA (deoxyribonucleic acid)- a
nucleic acid which stores genetic traits
in the proteins it codes for
 All living things contain DNA
 DNA is the blueprint for chemical
changes which take place in cells
– Type of cell which is formed, (muscle,
blood, nerve etc) is controlled by DNA
– Type of organism which is produced
(buttercup, giraffe, herring, human, etc) is
controlled by DNA
How Much DNA Is In OUR Cells?
 Chromosome-strands of DNA coiled tightly
 Human cell has 46 (23 pairs)
 23 from Mom
 23 from Dad
 Other organisms
have different
numbers of
chromosomes
2 Types of Cells

Somatic cells –all body cells
except sex cells
 Diploidchromosomes are in
pairs
 46=23 pairs for humans
 1 set (23) from mom, 1 set (23)
from dad

body cells
46 chromosomes
Gametes - sex cells
sperm
 Egg & sperm
23 chromosomes
 Haploid no pairs (only 23
single chromosomes total)
egg
23 chromosomes
Human Chromosomes

If all body cells contain the same # of
chromosomes, why are all cells so different?
 Different cells make different proteins due to
different “active” segments of DNA
– Heart cells make proteins needed for the heart to work
properly
– Brain cells make proteins needed for the brain to work
properly
Nucleotides

Nucleotides- subunits
of DNA made of:
–
–
–
1. Phosphate (PO4)
2. A ring shaped sugar
(deoxyribose)
3. Nitrogen base
Phosphate Group

The phosphate group
is the same in each
nucleotide
 It contains the
elements phosphate
and oxygen
Ring Shaped Sugar

The ring-shaped sugar is the
same in all nucleotides of
DNA
–
–

This sugar in DNA nucleotides
is deoxyribose
It is composed mainly of
carbon and hydrogen
Later you will see there is
another nucleic acid called
RNA in which the sugar is
ribose
Nitrogenous Bases
They are “nitrogenous” because they contain
nitrogen
 The 4 bases that a DNA nucleotide can have are

–
Adenine (A)
–
Thymine (T)
–
Cytosine (C)
–
Guanine (G)
Entire Nucleotides

These 3 subunits
combine to form 4
possible nucleotides in
DNA
 For example:
PO4
adenine
deoxyribose
A Nucleic Acid Strand
PO4

When many of these nucleotides
monomers are joined together,
PO4
which creates a nucleic acid
molecule called DNA
 Sequence and length of the
PO4
nucleotide chains determine the
proteins the DNA codes for
 Two types of nucleic acids are PO4
found in living organisms
–
–
DNA
RNA
sugar-phosphate
backbone
bases
DNA Structure

DNA usually consists of two
strands of nucleotides bonded
together, like a ladder
– The sugar-phosphate chains are the
outside “rails”
– The strands are held together by
chemical bond “rungs” between the
bases

In humans there are approximately
3 billion nucleotides in each strand
Strand #1
PO4
Strand #2
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
Chargaff’s Rule

He measured amounts of each base in various
organisms and found:
– % of adenine (A) = % thymine (T)
Adenine
Thymine
– % of cytosine (C) = % guanine (G)
Cytosine
Guanine
Chargaff’s rule told us that A bonds to T and C
bonds to G
 If 20% of strands is A, what %T? %C?

Strand #1
Strand #2
PO4
PO4
adenine
thymine
PO4
PO4
cytosine
guanine
PO4
PO4
PO4
PO4
Hydrogen bonds between bases
hold two strands together
3D Structure of DNA

Discovered by Watson and Crick
– Double helix- 2 strands of nucleotides
bonded together and twisted
– Discovery of this 3D structure helped
us determine the exact function of
DNA
bases
sugar-phosphate
chain
What is DNA Replication?

Replicate = make “exact” copies
– DNA replication- copying one double stranded DNA
molecule into two genetically identical copies
– All DNA must be
replicated before a
cell can divide. Why?
– Replication Animation
PO4
The strands
separate
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
Each strand builds up its partner by adding
the appropriate nucleotides
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
Enzymes and Replication

Helicase- enzyme that
unwinds DNA
 DNA polymerase-enzyme
that moves along each
strand and brings in bases
for new strand copy
DNA Replication Efficiency

Replication is very fast and accurate, but there can
be a mistake made
– Mutations-change in DNA
– Mutagens- substances that cause mutations
• X-rays
• Toxins
• Drugs
• UV light, etc.
Mutations

3 types of mutations that can
occur during DNA
replication:
– Insertions -extra
nucleotides
– Deletions –missing
nucleotides
– Substitutions –placement
of wrong nucleotides
 Can be helpful or harmful
mutations.
Insertion
Deletion
Substitution
How does DNA code for
proteins?
A Gene Codes for One Protein
Gene- a segment of DNA that
DNA has 1000’s of
codes for a protein
genes to make many
different types of
proteins
Why are proteins
important?
Protein - polymer of
amino acids
aa—aa—aa—aa—aa—aa—aa—aa = protein
RNA (Ribonucleic acid) is
Involved
_____DNA____ vs._____RNA___
Stores the genetic code in
the nucleus
Double stranded
Sugar of DNA nucleotides
is deoxyribose
A, C, G, T
“DNA is DNA”
Found in nucleus only
Transmits copies of the
genetic code to the rest of
the cell
Single stranded
Sugar of RNA nucleotides is
ribose
A, C, G, U (uracil) NO T!
Different forms: mRNA,
rRNA, tRNA
Found all over cell
DNA vs. RNA
Part 1 of Protein Synthesis:
Transcription

Transcription- copying of DNA triplets to mRNA
codons in the nucleus
– DNA complementary to mRNA
– ATA-CGG-AAT
(DNA triplets)
transcription in nucleus
UAU-GCC-UUA
(mRNA codons)
Transcription
cytoplasm
Translation
Part 2 of Protein Synthesis:
Translation:

Translation- converting mRNA copy to protein
which occurs at ribosomes in the cytoplasm
 UAU-GCC-UUA (3 mRNA codons)
translation by ribosomes
a.a.---a.a---a.a.
(amino acids of protein)
cytoplasm
Whole Process
ATA-CGG-AAT
(DNA triplets)
transcription in nucleus
UAU-GCC-UUA (3 mRNA codons)
translation at ribosomes
a.a.-a.a-a.a. (amino acids of protein)
tyrosine-alanine-leucine ??????
How do we know what amino acid
results?
The Codon Chart!!!
Protein Synthesis and Pain—What
is a Protein?
The Codon Chart
***How do we use the chart? There are 2 clues.
Amino Acids

Where do our cells get
these amino acids to build
the proteins?
– From FOOD!
– We eat proteins, then these
proteins are broken down
(metabolized) into amino
acids in our stomach.
– We reuse these amino acids
to build other proteins.