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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
NitrogenousBase
4 types: Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
2 strands so bases can pair upA binds T onlyC binds G only
P
S
P
S
A
C
Strand 1
P
S
P
S
T
G
Strand 2
Phosphates + sugars on the outside
Bases on the inside (Bases fit like puzzle pieces)
Remember
DNA is like an Oreo
Phosphates + sugars = cookiesBases = cream filling
BASE PAIRING RULES
What holds DNA together?
A T have two hydrogen bonds
P
S
P
S
A
C
Strand 1
P
S
P
S
T
G
Strand 2
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 semi-conservative 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
ScribesScripts
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 mRNATo 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
•DNA: GAG AAC TAG TAC•RNA: CUC UUG AUC AUG
For figuring out RNA:A binds UC binds G
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
Amino Acids
Protein
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
Cytoplasm of cell
Nucleus
DNAmRNA mRNA
TranslationTranslation
Ribosome reads the mRNA and puts together protein
“Translating mRNA into protein”
Cytoplasm
Nucleus
Ribosome
Process of Translation
1. mRNA moves out of nucleus
through nuclear pore
and into cytoplasm
2. mRNA attaches to a
ribosome
Cytoplasm
Nucleus
Ribosome
Process of Translation
3. Transfer RNA (tRNA) decodes the mRNA and brings
amino acids to build up the protein
tRNAAmino acid
Anticodon (3 bases on tRNA): Matches
up to codons on mRNA
Cytoplasm
Nucleus
Ribosome
Process of Translation
4. Protein (chain of amino acids) detaches from ribosome and goes off to work in the cell
Ribosome
tRNA Molecule
Polypeptide
¼ hemoglobin protein
Transfer RNA
(tRNA)Piece of RNA
Transfers 1 amino acid to protein being made at ribosome
Translation
RibosomeHelps 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
Translation
Genetic Code• Codon: group of 3 mRNA nitrogen bases
that code for a specific amino acid
DNA:GTT 3 NucleotidesCodon Chart
Amino acid: Gln
mRNA: CAA codon
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
The genetic code is said to be universal because it is the same in almost all organisms
Worm – AUG = methionine
Human – AUG = methionine
Example:CGU, CGC, CGA, CGG, AGA, & AGG
all code for arg
Central dogma of molecular biology
DNA RNA Protein
Directions to make proteins
are safely stored in the nucleus
Carries the directions to
the cytoplasm
Work to keep the cell alive
Transcription Translation
DNA: The Stuff of LifeDNA 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-
B5Person A: ATTGCACGATAACGAPerson 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.”