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DNADeoxyribonucleic Acid
Chapter 11
Page 287
What is DNA?
The information that determines an organisms traits.
DNA produces proteins which gives it “The power”
Many things contain and are made of proteins.
Skin, hair, bones, etc are made of proteins.
What is DNA? Cont’d
Enzymes are special proteins. Enzymes control chemical reactions
needed for life. DNA contains all the information for
making all and any proteins for human life.
DNA Structure: DNA is made of
repeating subunits called nucleotides.
Nucleotides have three parts:– Simple sugar– Phosphate group– Nitrogen base
DNA Structure The simple sugar is called deoxyribose. The phosphate group is made of
phosphate and oxygen. There are four possibilities to Nitrogen
bases:– Adenine (A)– Guanine (G)– Cytosine (C)– Thymine (T)
DNA Nucleotides join together
to form long chains. The phosphate group of
one nucleotide joins together with the deoxyribose sugar of an adjacent nucleotide.
The phosphate groups are thought of as the “backbone” of the chain
The nitrogen bases are thought of as teeth coming off the structure.
DNANitrogen bases
Nitrogen bases pair up– Adenine
and Thymine (A-T)
– Cytosine and Guanine (C-G)
Watson and Crick
First people to propose that DNA is made of two chains of nucleotides joined together by the nitrogen bases
They believed that the two strands are joined by complimentary bases
• A-T• C-G
They also proposed that DNA is put together like a zipper that is twisted.
When something is twisted like a spring, it is called a helix.
Because DNA has two strands it is called a Double Helix.
Importance of Sequencing
The sequence of the four different nucleotides determines what organism is created.
For instance – T-A-A-G-C-A Is different than – A-G-C-A-A-G
In English - E-A-R-T-H Is different than H-E-A-R-T– They have the same letters, just a different order
and mean different things.• Can you think of any other words that you can do this
with?
The closer the order is to another order, the closer the relationship between the two organisms.
Importance of Sequencing
Scientists can use the sequencing to find out evolutionary history.
For instance, gorillas and chimpanzees might have similar sequencing but chimpanzees and rose bushes would not be very similar.
DNA sequencing can also be used to show whether two people are related or not.
DNA sequencing can also be used to correlate someone to a crime scene.
END OF DAY 1
DNA Replication
DNA is copied – this is called replication
Without DNA replication, a new cell would only have half of it’s information.
All organisms undergo DNA replication
DNA Replication
Replication VIDEO
DNA Replication
Because of the pairing- if you have one strand, it is easy to predict the replicated strand.
T-A-G-C-C-G-T Would be replicated by matching T, with
A, G with C A-T-C-G-G-C-A
DNA Replication Remember: The nitrogen bases are held
together by hydrogen bonds There is an enzyme that goes to those
hydrogen bonds and breaks them This causes the double helix structure to break
apart or “Unzip” There are nucleotides that are floating around. These nucleotides are like puzzle pieces They each try to attach to the original
nucleotide.
DNA Replication
The unzipping continues until the entire strand is done.
The original DNA now has a complimentary strand.
The result is two DNA molecules which is identical to the original.
The end product is that there are two copies of the organism’s genetic makeup.
DNA to Protein
DNA encodes the instructions for making proteins.
Remember proteins make up your bones, skin, etc.
Enzymes are special proteins Enzymes control all chemical reactions
in an organism
DNA Replication
Proteins are made up of many amino acids
The order of nucleotides in each gene has information on how to make the string of amino acids which is a protein.
ESTIMATE: Each cell contains about 800,000 genes
RNA There are three key differences between
RNA and DNA1. RNA is single stranded – only half of a
zipper – DNA is double stranded – zipper
2. RNA is made of the sugar Ribose – DNA is made of deoxyribose
3. RNA has Uracil instead of Thymine – Both DNA and RNA have four nitrogen bases the difference is U vs T
RNA RNA has the job of copying DNA The goal of RNA is to create proteins There are three types, each with a
different job.– mRNA – Messenger RNA-copies DNA to
take it out in the cytoplasm– rRNA – Ribosomal RNA-works on
matching mRNA - to create the amino acids in the correct order
– tRNA – Transfer RNA- gives amino acids to rRNA to produce the protein.
mRNA
Messenger RNA is responsible for uncoding the DNA and creating RNA (in a process called transcription) for mRNA, rRNA, and tRNA to read.
Messenger RNA is responsible for bringing the information transcripted RNA to the cytoplasm.
WHY in the cytoplasm?
rRNA Ribosomal RNA are made of
ribosomes. Where are ribosomes found?
– In the cytoplasm. They are not bound to any one organelle.
rRNA attaches to the mRNA rRNA then begins to use the information
from DNA that mRNA brought out. rRNA uses the information to set up the
amino acids in the correct order.
tRNA
tRNA is the supplier tRNA gives amino acids to rRNA so that
rRNA can assemble the protein.
Review Questions
How does information from the DNA get to the cytoplasm?
How does the zipper get unzipped in DNA replication?
Who does the work in getting the amino acids to the worker?
What is the formal name of the worker
END OF DAY 2
Transcription Transcription’s purpose is to create a
single stranded RNA molecule rather than a double stranded DNA molecule.
This is needed to allow the single stranded RNA to be taken out of the nucleus by the mRNA to the cytoplasm.
Transcription
Transcription Tutorial / SHOW
Transcription mRNA VIDEO
Genetic Code with mRNA
In order to take the DNA and create a mRNA, there are special codes used.
In mRNA, three nitrogen bases together form a code – this is called a codon.
Looking ahead: this code is matched with an amino
acid. A string of amino acids form a protein.
Genetic Code with mRNA
Some codons code for information other than amino acids
UAA is an example of a stop codon. AUG is an example of a start codon. NOTE: For every one codon, there is
only ONE amino acid that can join.
Transcription Pictures
Transcription Pic’s
How does this work in the cell?
DNA
AMINO ACIDS TRANSPORTED BY tRNA
mRNA COPIES DNA INTO CYTOPLASM
rRNA USES PLAN FROM mRNA TO PUT AMINO ACIDS IN ORDER TO MAKE PROTEINS RIBOSOME
NUCLEUS
END OF DAY 3
Translation: From mRNA to Protein
The process of changing the information from an order of nitrogen bases in mRNA into the order of amino acids is called translation.
This takes place at the ribosomes in the cytoplasm
Translation
When mRNA enters the cytoplasm, ribosomes attach
For proteins to be made-20 different amino acids must be brought to the ribosomes.
This is what tRNA does – brings the amino acids to the mRNA strand
Translation
On the opposite side of the tRNA amino acid side is a set of three nucleotides that are the complement of the nucleotides codon.
Translation
These three nucleotides are called anticodons because they bond to the codon of the mRNA
The tRNA is made of only the anticodon and the amino acid.
Translation
When a match is made- a temporary bond is formed.
This places the amino acid in the correct position to enable it to bond with the next amino acid
Translation
The next tRNA bonds to it’s codon and then the two amino acid’s bond together.
The first amino acid then releases itself from the mRNA
Translation
This continues until a stop codon is reached.
Amino acid chains then become proteins when they are freed from the ribosome and twist and curl into complex three-dimensional shapes.
Translation
Translation VIDEO
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