Download DNA Replication

DNA Structure and Function
Review!
•Nucleus : “brain”
of the cell.
•Chromosomes:
found in the
nucleus.
DNA BIG Picture
• Chromosomes are made of DNA.
• DNA has your genes on it.
• DNA has the instructions for making all
proteins for the organism.
• DNA is unique to each individual.
• DNA determines how an organism looks and
functions (traits).
• Each human has about 30,000 genes on the
DNA.
DNA
Deoxyribonucleic acid
Located in the nucleus of a cell.
Is a type of nucleic acid.
Made up of repeating nucleotide subunits.
DNA Codes for Proteins
• All living things contain proteins. Proteins are
essential to all of life.
• ENZYMES ARE PROTEINS!!
• Enzymes control all the chemical reactions in an
organism and are extremely important
molecules in biology.
• DNA contains all of the information needed to
build all of the proteins for our bodies.
1 nucleotide looks like:
Phosphate
Group
Deoxyribose
Sugar
Nitrogenous
Base
4 types: Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
BASE PAIRING RULES
2 strands so bases can pair up
A binds T only
C binds G only
Strand 1
Strand 2
P
S
P
A
T
P
S
Remember
S
P
C
Phosphates + sugars
on the outside
G
DNA is like an Oreo
Phosphates + sugars = cookies
Bases = cream filling
S
Bases on the inside
(Bases fit like puzzle pieces)
What holds DNA together?
Strand 1
Strand 2
P
S
P
A
T
P
S
S
A
T have two
hydrogen bonds
P
C
G
S
G
C have three
hydrogen bonds
• Two strands of nucleotides twist
together  double helix
James Watson and
Francis Crick
discovered the double
helix structure (They
won the Nobel Prize)
How does DNA carry information?
• DNA carries information in the form of
nucleotide sequences.
• For example:
– The sequence ATATGCTCTA carries different
information from the sequence
CGGTATTAAC.
• Different combinations of the same 4
nucleotides creates a near infinite number
of unique genes.
DNA is complementary
Bases on one strand match up with the
bases on the other strand (A-T and G-C)
Example: Strand 1- ATG GGC CTA
Strand 2- TAC CCG GAT
DNA Replication
 During cell division
(interphase), chromosomes
replicate to form exact copies
to pass along to daughter cells.
 That means the DNA
replicates!
 The DNA unzips and 2 new
strands form.
 A complete, exact copy of
DNA is created.
 Each side serve as a template
for the other side (called semiconservative replication).
DNA never ever leaves the
nucleus
• DNA is the master copy of the
directions a cell needs to live so it
needs to be protected
DNA in
the
nucleus
is safe
But DNA
in the
cytoplasm
can be
destroyed
RNA
• Ribonucleic Acid
• Building
Blocks:nucleotides
• A nucleotide is:
– A sugar (ribose)*
– A phosphate
– A nitrogen base
• RNA has 4 nitrogen
Bases (just like DNA)
–
–
–
–
Adenine
Guanine
Cytocine
Uracil **
RNA is only a single
strand***
Three types of RNA****
• Messenger RNA (mRNA)copies info from DNA and
takes the message to the
cytoplasm.
• Ribosomal RNA (rRNA)makes up ribosomes,
assembles proteins.
• Transfer RNA (tRNA)transfers amino acids to the
ribosomes to become
proteins.
Protein Synthesis Overview
• Protein synthesis occurs in two
steps:
1. Transcription
2. Translation
Scribes
Scripts
Copy script for actors
Transcription
• Definition: RNA is made from 1 gene in
DNA
• The type of RNA made is called mRNA
(messenger RNA) because it sends a
message from DNA to the cytoplasm
DNA safe in
the nucleus
Uses mRNA
To send a
message to the
cytoplasm
Transcription
 Enzymes unzip one gene in DNA
 Match up bases to one side of a
gene in DNA
 mRNA detaches from the DNA,
DNA joins back together
 mRNA moves out of the nucleus
and into the cytoplasm
For figuring out RNA:
A binds U
C binds G
•DNA: GAG AAC TAG TAC
•RNA: CUC UUG AUC AUG
How does mRNA tell the cell what to do?
• mRNA is a message that codes for a protein
• Proteins are made in the cytoplasm (at the –
ribosomes)
• Translation (protein synthesis): Process of
making a protein
• Proteins are made up of amino acids (small
building blocks) -There are 20 different
types of amino acids
Protein
Amino Acids
DNA
mRNA
mRNA
Cytoplasm of
cell
Nucleus
Transcription
happens in
the nucleus.
An RNA copy
of a gene is
made.
Then the
mRNA that
has been made
moves out of
the nucleus
into the
cytoplasm
Once in the
cytoplasm, the
mRNA is used
to make a
protein
Translation
Ribosome
reads the
mRNA and
puts together
protein
“Translating
mRNA into
protein”
Nucleus
Process of Translation
1. mRNA moves
out of nucleus
through nuclear
pore and into
cytoplasm
2. mRNA
attaches to a
ribosome
Cytoplasm
Ribosome
Nucleus
Process of Translation
3. Transfer RNA
(tRNA) decodes the
mRNA and brings
amino acids to build
up the protein
tRNA
Amino
acid
Anticodon (3 bases on
tRNA): Matches up to
codons on mRNA
Cytoplasm
Ribosome
Nucleus
Process of Translation
Cytoplasm
4. Protein (chain
of amino acids)
detaches from
ribosome and
goes off to work
in the cell
Ribosome
Ribosome
tRNA Molecule
Polypeptide
¼ hemoglobin protein
Translation
Transfer
RNA
(tRNA)
Piece of RNA
Transfers 1 amino
acid to protein
being made at
ribosome
Translation
Ribosome
Helps line up the
mRNA and tRNA
Part of the ribosome is actually
made of RNA.
Can you guess what they are
going to call this type of
RNA?
rRNA
Genetic Code
• Codon: group of 3 mRNA nitrogen bases that
code for a specific amino acid
Codon Chart
DNA:GTT 3 Nucleotides
mRNA:
CAA  codon
Amino acid:
Gln
tRNA: GUU  anticodon
There are 64 codons that
code for 20 amino acids …
43 = 64 different possible
codons
How is this possible? ….
More than one codon may
code for an amino acid
Example:
CGU, CGC, CGA, CGG, AGA, & AGG all
code for arg
The genetic code is said to be universal because
it is the same in almost all organisms
Worm – AUG = methionine
Human – AUG = methionine
Central dogma of molecular biology
Translation
Transcription
DNA
Directions to
make proteins are
safely stored in
the nucleus
RNA
Carries the
directions to
the cytoplasm
Protein
Work to keep
the cell alive
DNA: The Stuff of Life
DNA Structure and Gene Expression
While it might be hard to
see, it’s in there, and it
is in every single cell of
every living organism on
our planet.
What is the relationship between,
chromosomes, DNA and genes?
All of the genetic information is stored in the nucleus of
every cell in structures called “Chromosomes”
For humans, we have 23 pairs of chromosomes in virtually
every cell in our body
Nucleotide Sequencing
The genetic code in DNA is based on the
sequence of these letters. Each gene will
have a specific number of nucleotides/base
pairs (length) and sequence of letters.
For example:
Gene 1204-B5
Person A: ATTGCACGATAACGA
Person B: TCGATCAAACGCATA
Although they have same number of base pairs
in the same gene, the sequence of letters
makes them different, thus a different version
of that trait will be expressed.
1. Use the ribosome sheet to create
your own sentence. It must have at
least 5 words and be school
appropriate.
2. Write the mRNA sequence for your
“protein.”
3. Write the DNA sequence for your
“protein.”