Download Unit 5 DNA and 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
• nitrogenous base
– 4 kinds:
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
adenine, thymine,
guanine, 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
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)
• 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 =
adenine,
thymine,
guanine,
cytosine
• N bases =
adenine,
uracil,
guanine,
cytosine
The DNA Code & Protein Synthesis
• What is a gene?
– a section of DNA that
codes for the synthesis
(making) of a specific
protein
• Which part of DNA
actually carries the code?
– the nitrogen bases
• & their order
– If the sequence is changed 
the amino acid (usually)
changes  & the 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
• What does transcription make?
– A single-stranded messenger
RNA (mRNA)
• made from instructions/order of the
bases in the DNA
• 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
http://www.stolaf.edu/people/
giannini/flashanimat/molgen
etics/transcription.swf
mRNA
• What is a codon?
– 3 consecutive bases on
mRNA that codes for a
particular amino acid
• Some amino acids have more
than one codon
– How can we figure out the amino
acid coded for by a codon?
» a codon chart
mRNA Codons & Amino Acids
mRNA Codons & Amino Acids
mRNA Codons & Amino Acids
Translation
• What is translation?
– process of making proteins from mRNA codons
(with help of tRNA/ transfer RNA anticodons &
ribosomes)
• When does translation occur?
– when mRNA from the nucleus joins with ribosomes
• Where does translation happen?
– in the cytoplasm
http://www.stolaf.edu/people/giannini/fl
ashanimat/molgenetics/translation.swf
Translation
• What are the steps in translation?
1. anticodon on tRNA:
•
•
joins with complementary mRNA codon
carries amino acid specified by the codon on mRNA to
ribosome
2. Amino acids line up & bond to form protein
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 =
mRNA codon =
amino acid =
anticodon (on tRNA) =
TAC CCA GAT CCG ACT
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
• What happens in
a point mutation?
–one nucleotide
(base) is
replaced by
another
» does not cause
“frame shift”
~sometimes amino
acid & protein can be
the same
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