Download DNA & Protein Synthesis

Unit 6: DNA & Protein Synthesis
Ch. 28: DNA—Life’s Code
DNA = Deoxyribonucleic Acid
Describing DNA
• Who first
described DNA?
– James Watson &
Francis Crick
• What shape did
they use to
describe DNA?
– double helix
DNA is a Polymer…
• What is the monomer
that repeats to make
DNA?
–nucleotide
What are the parts of a nucleotide?
• phosphate group
• sugar (deoxyribose)
• nitrogenous base
– 4 kinds:
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
– base gives name
to nucleotide
adenine, thymine,
guanine, or cytosine
A Model of DNA
• Is a DNA molecule singlestranded or double
stranded?
– double-stranded
• What parts make up the
strands?
– “backbone”/sides
• sugars & phosphates
– “rungs”/steps
• nitrogenous bases
– always paired as:
» A-T
» G-C
DNA Structure Video
• Strands are complementary (A-T & G-C) &
antiparallel (opposite directions/upside down)
Where is DNA found in
eukaryotic cells?
• DNA is contained in chromosomes
(chromatin) within the nucleus
sugar-phosphate “backbone” & nitrogenous base “rungs”
DNA Replication
• What is another word for replication?
– copying
• Why must DNA replicate?
– so when cell divides, each new
cell gets a copy of DNA
http://www.stolaf.edu/peo
ple/giannini/flashanimat/m
olgenetics/dna-rna2.swf
DNA Replication
• When does DNA replicate?
– before the cell divides (before mitosis or meiosis)
• Where does DNA replicate?
– inside the nucleus
What are the steps in DNA replication?
• 1. DNA molecule unzips between bases
forming two “parent strands”
What are the steps in DNA replication?
• 2. The “parent”
strands act as
templates (guides)…
– “new” nucleotides are
paired up with the
complementary base
on the “parent” strand
•
forming a
complementary
daughter strand
–
ex. “G” pairs with “C”
T
C
What are the steps in DNA replication?
• 3. Now, there are 2 exact copies
of the original DNA molecule.
– & when the cell divides, each
“new” daughter cell gets a copy
What are the
steps in DNA
replication?
T
C
DNA Replication Video
Let’s Practice… Predict the next base…
Let’s Practice… Finish the replications…
Let’s Practice… Finish
the replications…
Deoxyribonucleic Acid vs. Ribonucleic Acid
DNA
RNA
• sugar =
deoxyribose
• sugar =
ribose
• double
stranded
• single
stranded
•CANNOT
•Can move
leave nucleus between
nucleus &
cytoplasm
• N bases =
• N bases =
adenine,
adenine,
thymine,
uracil,
guanine,
guanine,
cytosine
cytosine
The DNA Code & Protein Synthesis
• What is a gene?
– section of DNA that codes
for synthesis of a specific
protein
• Which part of DNA carries
the code for a protein?
– the nitrogen bases
• & their order
– change sequence  amino
acid (usually) changes  &
protein made (usually) changes
The DNA Code & Protein Synthesis
• So, the big question is…
– How does the DNA code in a cell’s nucleus
get to the ribosomes where proteins are
synthesized?
• transcription & translation
Transcription
• What is transcription?
– DNA code is
“transcribed”/copied
into mRNA codons
• When does
transcription happen?
– when a protein is
needed
• Where does
transcription happen?
– in the nucleus
Transcription
http://www.stolaf.edu/people/
giannini/flashanimat/molgen
etics/transcription.swf
• What does transcription make?
– A single-stranded messenger RNA (mRNA)
• made from instructions/order of the bases in the DNA
Transcription
• What are the steps in
transcription?
1. DNA unzips
2. free RNA nucleotides
pair w/ exposed bases
on DNA
•
until “stop codon” is
reached
3. mRNA separates from
DNA
•
& moves out of nucleus
–
to ribosome in cytoplasm
4. DNA strands rejoin
http://www.stolaf.edu/people/
giannini/flashanimat/molgen
etics/transcription.swf
mRNA Carries DNA’s Code Using “Codons”
• What is a codon?
– 3 consecutive bases
on mRNA that codes
for a particular
amino acid
• 64 possible combos
– Some amino acids have
more than one codon
mRNA Carries DNA’s Code Using “Codons”
• How can
we figure
out the
amino
acid
coded for
by a
codon?
– a codon
chart
What amino acid does
the AUG codon code for?
mRNA Codons & Amino Acids
• What amino acid does the AUG codon code for?
It must
be in
this row
It must be
It must be
in this
in this
square
amino acid
mRNA Codons & Amino Acids
Translation
• What is translation?
– process of reading
mRNA codons to
synthesize proteins
• with help of tRNA
(transfer RNA) &
ribosomes
• When does translation
occur?
– when mRNA from the
nucleus joins with
ribosomes
• Where does translation
happen?
– at ribosomes in the
cytoplasm
http://www.stolaf.edu/
people/giannini/flash
animat/molgenetics/tr
anslation.swf
Steps of Translation
1. mRNA comes from the
nucleus & joins with
ribosome in cytoplasm
2. Ribosome “reads” the
codon until it finds the
start codon (AUG)
3. tRNA (with complementary
anticodon) joins to the
mRNA codon
– tRNA carries the amino
acid specified by the
mRNA codon
http://www.stolaf.edu/
people/giannini/flash
animat/molgenetics/tr
anslation.swf
Steps of Translation
4. Ribosome moves along mRNA reading
each codon until “stop” codon is reached
–
tRNA brings each amino acid
5. Amino acids line up & bond to form
polypeptide
6. Polypeptide chain forms protein (3-D)
–
Shape of protein is related to its function
transcription
translation
DNA
codon
tRNA
anticodon
mRNA
codon
mRNA
codon
Let’s Practice… What would the
mRNA strand made during
transcription look like?
What amino acids would be coded
for using this mRNA?
What would the anticodons on
the tRNA be for each amino acid?
Let’s Practice…
• Given the DNA sequence below, determine the:
1. mRNA codon sequence
2. amino acids that would be coded for by each
codon
3. anticodons on each tRNA which allowed it to
“bring” that amino acid (using the mRNA codons)
•
•
•
•
DNA =
TAC
mRNA codon = AUG
amino acid = Met/start
tRNA anticodon = UAC
CCA TTG GAT CCG ACT
GGU AAC CUA GGC UGA
Gly
Asn Leu Gly
stop
CCA UUG GAU CCG ACU
Mutations
• What are mutations?
– mistakes/changes in a gene
on a chromosome
• can occur spontaneously
during replication
• can be caused by mutagens
(such as radiation, high
temperatures, or chemicals)
• often corrected, but not always
– once occurs, copied as if correct
– can cause different protein
Types of Mutations
• What are the 3 types of mutations?
1. deletion
• What happens in a deletion mutation?
– a nucleotide (base) is left out
» causes “frame shift”
~moves nucleotides after the deletion to the left causing a
different protein to be formed
Types of Mutations
2. insertion
• What happens in an insertion mutation?
–a nucleotide (base) is added in
» causes “frame shift”
~moves nucleotides after the insertion to the right causing a
different protein to be formed
Types of Mutations
3. point (base substitution)
• What happens in a point
mutation?
–one nucleotide (base) is
replaced by another
» affects only 1 amino acid &
does not cause “frame shift”
» sometimes amino acid &
protein can be the same
(“silent mutation”)
» protein may be able to function
normally or nearly normally
Sickle Cell Mutation
• What does the sickle cell mutation do?
– affects hemoglobin
• What type of mutation causes sickle cell?
– A point mutation
• changes one amino acid
– changes the protein
“Silent” mutation (no change in polypeptide)
(point mutation)