Homework
• Due Monday 3/12:
• Read pages: 527-528
• Answer questions 3, 4, 5.
Remaining Questions
1. We learned about defective chromosomes that
cause genetic diseases - what caused these
chromosomes to become defective?
2. We learned about traits/diseases. Some are
dominant and some are recessive. What makes
something dominant and something else
recessive?
To answer these questions, we must look more
closely at what DNA actually does.
DNA in Action
DNA Replication and Gene Expression
DNA Review
• Remember that DNA is made up of
chains of nucleotides. A DNA molecule
contains four nitrogen bases: Adenine,
Cytosine, Guanine, Thymine.
• These chains are held together shaped
in a double helix.
• It has two matching strands that line up
next to each other. In HORIZONTAL
BONDING:
• A–T
• C–G
• G–C
• T–A
• Remember that in VERTICAL
BONDING, they can be in any order.
Vocabulary: Complement Chain
• Because DNA is a double
helix, each polynucleotide
chain is matched with a
specific other chain and no
other chain is possible.
• These two matching chains
are called complements
because they complement
each other and make up a
full DNA molecule together.
What holds DNA together?
Within each chain
• Each polynucleotide chain is
held together by strong
covalent bonds.
Between two complement
chains
• The two complement chains
are held together by weak
hydrogen bonds.
So what?
DNA Replication
• Remember this?
(Please say yes)
• Earlier, we just said that
somehow the DNA
replicates during S-phase
so that the cell can do
mitosis and each
daughter cell can have a
full copy of DNA.
• How does the DNA do
that?
DNA Replication #1
• The first step of DNA replication is UNZIPPING the
double-stranded DNA.
“Zipped”
“Unzipped”
DNA Replication #2
• The second step
of DNA
replication is
copying each
individual chain.
• We are then left
with two
identical
double-stranded
DNA molecules.
A
A
B
B
Where do the new DNA building
blocks come from?
• In order for humans to do DNA replication,
they must have a store of extra nucleotides to
build up new DNA molecules with.
• These come from two sources:
1. Humans can produce A, C, G, T blocks on
their own
2. Humans eat DNA in almost any food they
consume. Anything that was alive has DNA –
Strawberries, beef, grain-products, etc.
Review
• What is a single building block
A (mono)nucleotide
of a DNA molecule called?
• Two matching strands are
Complement strands
called…?
• What is the complement of
TTCTAGCA
AAGATCGT?
• What are the bonds that hold
two polynucleotide chains
Weak Hydrogen bonds
together?
double-stranded DNA molecule
• How does DNA replication Each
splits. Each chain is then copied to
produce two identical doublework?
stranded molecules.
OGTs (10th grade)
• Packets
• Time to meet
• Hw Exempt
Hw – Worksheet. Due tomorrow
Gene Expression
1.
2.
3.
4.
More DNA background
RNA
Transcription
Translation
DNA background
• Each human cell contains DNA in its nucleus.
• Each cell contains identical DNA to every other
cell.
• No one else has the exact same DNA as
another person (unless they are identical
twins).
Just how much DNA is there?
• Each human cell contains 46
different chromosomes.
• Each chromosome contains
thousands of different genes.
• Each gene is made up of a few
thousand individual base pairs.
• In total, each nucleus contains
around 3 billion base pairs.
RNA – Ribonucleic Acids
• RNA is very similar to DNA.
• Similar- They both contain
sugars, phosphates, and
nitrogen bases such as
Adenine, Cytosine, and
Guanine.
• Different- There are two
important differences.
1. RNA contains Uracil
instead of Thymine. Uracil
behaves exactly like
Thymine (it bonds with
Adenine).
2. RNA is made up of a single
strand, not a double
strand.
How does the DNA direct the activities
of the body?
• DNA controls which proteins are produced.
• Proteins serve many different purposes in the
body (hormones, enzymes, structure, etc).
• By controlling the production of proteins, the
DNA indirectly controls everything that goes
on in the body.
How does the DNA control protein
production?
1. Transcription
2. Translation
Transcription
1. The DNA unzips.
2. The body makes a
complement of one of the
two strands (called the
template) out of RNA.
3. This complement is called
mRNA, or Messenger RNA.
4. The mRNA is much shorter
than a full chromosome and
just matches a single gene.
5. When the RNA reaches a
certain sequence of DNA (the
stop code) it detaches from
the DNA.
6. The DNA rezips
This process occurs in the
nucleus.
Video of Transcription
• http://www.youtube.com/watch?feature=end
screen&v=AGzsgTMgSog&NR=1
Key points to remember about
Transcription
1. The product of transcription is mRNA.
2. The mRNA only copies one of the two DNA
strands – the template. This is different than
in DNA replication when both DNA strands
were copied.
Questions
1. If the DNA template was AAC-GTC-GTA-AGT ,
what is the mRNA transcript? UUG-CAG-CAU-UCA
2. If the DNA template was TTG-GCC-TAA-CGA,
what is the mRNA transcript? AAC-CGG-AUU-GCU
Trick Questions
1. If the DNA template was AAG-GUU-TGT-GAC,
what is the mRNA transcript?
Impossible- DNA does not contain Uracil.
2. If the other strand (non-template) was
ATG-CGC-TAT-GTC, what is the mRNA
transcript?
This is tricky because the problem gives you the non-template. Therefore, you
must first figure out the template- TAC-GCG-ATA-CAG. Then you must find the
mRNA transcript: AUG-CGC-UAU-GUC.
Alternatively, you can realize that mRNA is the same as the non-template DNA
strand except that T is replaced with U.
Transcription and Translation videos
• http://www.youtube.com/watch?v=_6Rrymt6
XwI
• http://www.youtube.com/watch?v=983lhh20r
GY
Translation
• After the mRNA is
completed, it exits the
nucleus and enters the
cytoplasm.
• In the cytoplasm, it finds
a ribosome (a protein
factory).
Inside the ribosome
• The ribosome begins
reading the mRNA.
• Each 3-base group of
the mRNA is called a
codon.
• Each codon will match
with a specific tRNA.
tRNA – Transfer
RNA
• A tRNA is a much
smaller piece of RNA
than an mRNA.
• The tRNA is made up of
a long string of RNA
bases. It also contains
Uracil instead of
Thymine.
tRNA
• The tRNA has two important
ends:
1. The Anticodon. This is the
side of the tRNA that contains
a three-base sequence that
will match with a codon from
the mRNA
2. The Amino Acid Binding Site.
This part of the tRNA binds to
a particular amino acid. There
are twenty different amino
acids.
Building a protein
• Step 1: Inside the ribosome, the tRNA with the
matching anticodon bonds temporarily with the mRNA.
It brings along its amino acid.
• Step 2: A second tRNA joins and brings along its amino
acid. Those two amino acids bond together.
• Step 3: The first tRNA exits, leaving behind its amino
acid, connected with the second amino acid. (It will go
find its amino acid and be reused later)
• Step 4: The ribosome reads the next codon, brings in
the next tRNA, return to step 1.
• Step 5: This is repeated until the ribosome finds a stop
codon. Then the completed protein is released and
goes to perform its job in the body.
Draw it
• http://www.youtube.com/watch?v=983lhh20r
GY
Review Qs
• How many bases are in a codon?
• How many amino acids does a single codon
code for?
• How many different amino acids are there?
• How many bases are in an anticodon?
• Which contains Uracil- codons, anticodons,
both or neither?
Translating codons to amino acids
I will use this one
Translating codons to amino acids
• Key points to remember:
1. There are more possible
codons (64) than amino
acids (20), so it is
possible that different
codons can refer to the
same amino acid.
2. Stop codons - mean that
you have reached the
end of amino acid chain.
This is the sign for the
ribosome to release that
chain of amino acids.
3. These charts are for
codons, not anticodons!
Is it possible for a single mRNA strand to
produce multiple amino acid chains?
Yes.
If one of the codon in the middle of an mRNA
strand codes for “STOP”, then the current
amino acid chain is released and the next
codons begin a new chain.
Example: UUU-AUU-UGA-UAC-AAG
Phe-Ile STOP Tyr-Lys
HW Sheet