Download DNA and replication

DNA
(Deoxyribonucleic Acid)
• DNA is located in the nucleus of cells
• DNA is organised into chromosomes
• A gene is a segment of DNA on a chromosome, that codes for a
specific protein (trait).
-it codes for individual features and bodily functions
-The protein determines what trait the gene produces (eg. Hair
colour, skin colour, sex) Units of heredity
• The genetic code is determined by the order of the bases (chemical
code) in the gene, this determines the type of protein produced
AMAZING DNA FACTS…
• DNA from a single human cell
extends in a single thread for
almost 2 meters long!!!
• It contains information equal to
some 600,000 printed pages of
500 words each!!!
(a library of about 1,000 books)
Genetic material of cells…
• GENES – units of genetic material that CODES
FOR A SPECIFIC TRAIT
• DNA is a type of NUCLEIC ACID that is made
up of repeating molecules called
NUCLEOTIDES
• The chemical nature and structure of DNA
remained a mystery until the 1940’s
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
4 different bases
A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the structure
of the DNA molecule from Franklin’s X-ray by
building a model
(1953)
1953 | 1962
Watson and Crick … and others…
Watson & Crick proposed…
•DNA is made of 2 long strands of nucleotides arranged in a
specific way called the “Complementary base pairing
Rule”
•DNA had specific pairing between the
nitrogen bases (there are 4 bases):
•ADENINE – THYMINE
•CYTOSINE – GUANINE
• This allows DNA to replicate-make a copy of itself
DNA
• Double strand twists into a double helix
– weak bonds between nitrogen bases join the 2
strands
• A pairs with T
– A :: T
weak bonds
• C pairs with G
– C :: G
– the two strands can
separate when our
cells need to make
copies of it
DNA Double Helix
5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
2
3
P
1
T
5
A
P
3
O
O
P
5
O
3
5
P
BASE-PAIRINGS
H-bonds
G
C
T
A
DNA Double Helix
A ladder that is twisted=double helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
• https://www.youtube.com/watch?v=uXdzuz5Q-hs
• https://www.youtube.com/watch?v=o_-6JXLYS-k
HELIXHELIX
Let’s build some
DNA!
Genetic Diversity…
• Different arrangements
of NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among living
organisms.
The Code of Life…
• The “code” of the chromosome is the SPECIFIC ORDER
that bases occur and is important in coding genetic
information
A T C G T A T G C G G…
DNA is coiled tightly to form
chromosomes
Nucleic Acids
• Function:
– genetic material
• stores information
– genes
– blueprint for building proteins
» DNA  RNA  proteins
DNA
• transfers information
– blueprint for new cells
– blueprint for next generation
proteins
Nucleic Acids
Examples
– DNA
• DeoxyriboNucleic
Acid
– RNA
• RiboNucleic Acid
RNA
Nucleic acids:
Information molecules
2006-
• Go to:
http://www.visionlearning.com/en/library/Biology/
2/Nucleic-Acids/63
Questions
1. What are the two types of nucleic acids?
2. What is the main difference between DNA and
RNA
Extension:
3. What is the difference in function between DNA
and RNA?
Nucleic acids
• Building block =
nucleotides
nucleotide – nucleotide – nucleotide – nucleotide

5 different nucleotides


different nitrogen bases
A, T, C, G, U (U is only found in RNA)
sugar
phosphate
N base
Nitrogen bases
I’m the
A,T,C,G or U
part!
Nucleotide chains
• Nucleic acids
sugar
N base
sugar
N base
phosphate
– nucleotides chained into
a polymer
• DNA
– double-sided
– double helix
– A, C, G, T
• RNA
– single-sided
– A, C, G, U
phosphate
strong bonds
sugar
N base
sugar
N base
phosphate
phosphate
RNA
Cell Summary
• Cells have 3 main jobs
– make energy
• need food + O2
• cellular respiration & photosynthesis
• need to remove wastes
– make proteins
Our organelles
do all those
jobs!
• need instructions from DNA
• need to chain together amino acids & “finish”
& “ship” the protein
– make more cells
• need to copy DNA & divide it up to daughter cells
Cells need to make more cells!
• Making more cells
– to replace, repair & grow,
the cell must…
• copy their DNA
• make extra organelles
• divide the new DNA & new
organelles between 2 new
“daughter” cells
– organelles that do this work…
• nucleus
• centrosomes
DNA replication
• Copying DNA
– pairing of the bases
allows each strand to
serve as a pattern for a
new strand
Newly copied strands
of DNA
DNA Replication
• DNA must be copied to pass genetic
information on to new daughter cells
• The complementary base pairing rule
allows us to explain this process
• The DNA molecule produces 2
IDENTICAL new complementary strands
following the rules of base pairing:
A-T, G-C
•Each strand of the
original DNA serves as a
template for the new
strand
• The DNA is first unwound and separated by a
special enzyme-it separates down the middle like
a zipper being undone
• Each strand is used as a template by another
enzyme which lays down new nucleotides
according to the complementary base pairing rule
• Each DNA molecule now contains one
old/parent/template strand and one new strand
DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two strands of
the parental molecule
separate, and each
functions as a template for
synthesis of a new
complementary strand.
.
DNA Template
Parental DNA
New DNA
PO4
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
18
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
https://www.youtube.com/watch?v=zdDkiRw1PdU
DNA to protein
• DNA provides a plan for all the possible proteins in a
cell
• Proteins are made of amino acids and act as enzymes
and make up the plasma membrane among other roles
• It is the order of base pairs in DNA that code for the
order of amino acids in proteins
19
The sequence of bases in DNA forms the
Genetic Code
A group of three bases (a
triplet) controls
the production of a particular
amino acid in
the cytoplasm of the cell
The different amino acids and
the order in which they are
joined up determines the sort
of protein being produced
This is a small, imaginary protein molecule showing
how a sequence of 5 different amino acids could
determine the shape and identity of the molecule
Ser-Cyst-Val-Gly-Ser-Cyst Ala
Val
Val-Cyst-Ser-Ala-Ser-Cyst-Gly
Val- Cyst-Ala-Ala-Ser
Each amino acid (Serine, Cysteine, Valine, Glycine and
Alanine) is coded for by a particular triplet of bases
For example
Guanine
Thymine (Uracil)
Adenine
Codes for
Valine
Triplet code
22
This is known as the triplet code- code of three bases
Each triplet codes for a specific amino acid
GCA - GTA - GGC - GGA - CGC - CCA - CTGAla
Val
Gly
Gly
Arg
Pro
Leu
The amino acids are joined together in the correct
sequence to make part of a protein
Such a sequence on a DNA molecule is called a gene
Ala Val
Gly
Gly Arg
Pro
Leu
Functions of proteins
The proteins build the cell
structures
They also make enzymes
The DNA controls which
enzymes are made and
the enzymes determine
what reactions take place
The structures and reactions in
the cell determine
what sort of a cell it is and what
its function is
So DNA exerts its control through the enzymes
Nucleolus
Nucleus
– surrounded by a double membrane (nuclear
envelope), perforated with nuclear pores
– contains DNA & nucleolus (stores RNA
nucleotides)
– functions to separate DNA from rest of cell
DNA
Why organelles?
 Specialized structures
 specialized functions
mitochondria
 cilia or flagella for locomotion
 Containers
 partition cell into compartments
 create different local environments
chloroplast
 separate pH, or concentration of materials
 distinct & incompatible functions
 lysosome & its digestive enzymes
 Membranes as sites for chemical reactions
Golgi
 unique combinations of lipids & proteins
 embedded enzymes & reaction centers
 chloroplasts & mitochondria
ER
cytoplasm
jelly-like material holding
organelles in place
nucleus
protects DNA
controls cell
ribosomes
builds proteins
mitochondria
make ATP energy
from sugar + O2
cell membrane
cell boundary
controls movement
of materials in & out
recognizes signals
ER
helps finish proteins
makes membranes
Golgi apparatus
finishes, packages
& ships proteins
Ribosomes
• Function
– protein factories
– read instructions to build proteins from DNA
• Structure
– some free in cytoplasm
– some attached to ER
Ribosomes on ER
Ribosomes
Site of protein
synthesis
cytoplasm
jelly-like material holding
organelles in place
nucleus
protects DNA
controls cell
ribosomes
builds proteins
mitochondria
make ATP energy
from sugar + O2
cell membrane
cell boundary
controls movement
of materials in & out
recognizes signals
ER
helps finish proteins
makes membranes
Golgi apparatus
finishes, packages
& ships proteins
Endoplasmic reticulum (ER)
– interconnected network of membranes
extending from nucleus to plasma
membrane
nucleus
control cell
protects DNA
cytoplasm
jelly-like material
around organelles
nucleolus
make ribosomes
endoplasmic reticulum
processes proteins
makes membranes
ribosomes
make proteins
Golgi apparatus
finish & ship
proteins
mitochondria
make ATP in
cellular respiration
cell membrane
cell boundary
controls movement
of materials in & out
recognizes signals
cell wall
support
chloroplast
make ATP & sugars in
photosynthesis
endoplasmic
reticulum
nucleus
protein
on its way!
DNA
RNA
vesicle
TO:
TO:
TO:
vesicle
ribosomes
TO:
finished
protein
protein
Making Proteins
Golgi
apparatus
Genes (DNA)
are needed
to run bodies every day…
to make you and me…
to make new cells…
to make babies!
G
T
A
A
C
G
T
C
G
A
T
C
A
Replication Quiz
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
1. Why is replication necessary?
So both new cells will have the correct DNA
2. When does replication occur?
During interphase (in mitosis, cell division)
3. Describe how replication works.
Enzymes unzip DNA and complementary
nucleotides join each original strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
Check-up Questions: Ribosomes, cells
& genetic diversity
1. What does a ribosome do?
2. Compare and contrast transcription and
translation
3. What are the three main jobs of a cell?
4. Explain how nucleotides are related to the
diversity of life on Earth
Check-up Questions: DNA replication
1. When is DNA replication going to occur?
2. Explain why DNA replication needs to
occur at this time
3. Draw a diagram that shows how a DNA
molecule “unzips” and then produces
two new molecules
4. Explain how the DNA molecule makes an
exact copy of itself during replication
5. Where does DNA replication take place,
in eukaryotic cells?
6. Use the complementary rule to create
the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Check-up Questions: DNA is a code
1.
2.
3.
4.
5.
What are the 5 different types of nucleotides?
Explain what “the code of life” refers to
Compare and contrast DNA & RNA
Describe the “complementary rule”
When was the DNA molecule first described
correctly, and by whom?
6. Complete the following complementary base
pairs:
A–
C–
GT-
Check-up Questions: genetics
1.
2.
3.
4.
What type of organisms have DNA in their cells?
Which cells contain DNA?
In eukaryotic cells, where is the DNA found?
Draw a diagram to show the difference between
a chromosome, a gene and a nitrogen base
5. What are the two functions of genetic material?
6. What are the two examples of nucleic acids?