Download Chapter 9 DNA: The Genetic Material Read 192

DNA, RNA &
Protein Synthesis
What is DNA?
• The hereditary material in the nucleus of
cells that tells the cell when to make
proteins and what proteins it should make.
• Regions of DNA that code for proteins are
called genes.
• These proteins give organisms their traits,
such as eye color.
• DNA stands for deoxyribonucleic acid.
DNA Structure
• Discovered in 1953 by James Watson and
Francis Crick.
• DNA is a double-helix = 2 strands twisted
around each other like a spiral staircase.
• DNA is made of repeating subunits called
nucleotides.
• Nucleotides have 3 parts:
– Deoxyribose sugar
– Nitrogen base
– Phosphate group
DNA Nucleotide
DNA Structure continued…
• The sides of the DNA ladder are repeating
phosphates and sugars.
• The steps of the ladder are the nitrogen
bases.
• There are 4 different nitrogen bases in
DNA:
– Adenine
– Guanine
– Cytosine
– Thymine
Purines = Have a double ring structure
Pyrimidines = Have a single ring structure
Nitrogen Bases in DNA
Complementary Base Pairing
• Watson and Crick discovered that the
following base pairing rule exists in DNA
structure:
– Adenine is complementary (fits together) with
Thymine
• Held together by 2 hydrogen bonds
– Cytosine is complementary with Guanine
• Held together by 3 hydrogen bonds
• Each pairing includes one purine and one
pyrimidine.
Label the small portion of DNA
shown below:
Label the following:
• Sugars
• Phosphates
• Nitrogen bases
• Hydrogen bonds
Build a DNA Model
•
•
•
•
•
•
•
Black= sugar
White hollow= phosphate
White solid= hydrogen bond
Blue= cytosine
Green= thymine
Orange= adenine
Yellow= guanine
Make the sequence for ½ of the DNA
CTGGACT
• If the sequence of half of a DNA strand is
TAGGCC, draw the entire DNA strand.
Label the phosphate groups, deoxyribose sugars,
nitrogen bases, and hydrogen bonds.
Replication
• During interphase, chromosomes create new
chromatids. This process of making new DNA
strands is called replication.
• This process happens in the nucleus of the cell.
• Each new DNA produced has ½ from the original
strand and ½ that is newly built.
• DNA helicase breaks the hydrogen bonds that
hold the 2 strands of DNA together.
• DNA polymerase forms the new halves of DNA
by putting the correct nucleotides into position.
It also proofreads the new DNA built for any
errors.
• This process occurs once in a cell’s lifetime.
Let’s Practice Replication!
• Build the DNA model with the sequence
GTTCA.
• G=yellow
• T=green
• C=blue
• A=orange
Transcription
• Transcription is the making of RNA by using the
DNA code as a template.
• RNA is single stranded so only ½ of the DNA is
used as a template. This half is called the sense
strand. The other is the non-sense strand.
• RNA polymerase starts at the promoter on the
DNA and builds the new strand of RNA until it
reaches the termination signal.
• RNA produced leaves the nucleus through nuclear
pores to enter the cytosol. Why can it leave?
• 3 types of RNA are produced: messenger RNA
(mRNA), ribosomal RNA (rRNA) and transfer RNA
(tRNA)
Contrasting DNA and RNA
RNA
DNA
•
•
•
•
2 strands
Deoxyribose sugar
Remains in the nucleus
Bases
– ATCG
A pairs with T
G pairs with C
•
•
•
•
1 strand
Ribose sugar
Exits nucleus
Bases
– AUGC
A pairs with U
G pairs with C
Let’s Practice Transcription!
• Build the DNA model with the sequence
CTGGATC.
• G=yellow, T=green, C=blue, A=orange
U= purple
ribose=purple pentagons
• The side of the DNA listed above is the
sense strand.
• If the promoter is after the 1st “C” and the
termination signal is before the last “C”, what
is the RNA strand produced?
3 Types of RNA
1. mRNA (messenger)- carries the
DNA’s instructions for making proteins
out of the nucleus to the ribosomes in the
cytosol.
• Every 3 nucleotides on mRNA is called a
codon. Each codon codes for an
amino acid.
– See codon table
2. tRNA (transfer)- carries a specific
amino acid on one end and an anticodon
on the other end. The anticodon
complements the codon on mRNA.
Draw the tRNA structure:
3. rRNA (ribosomal)- Along with protein,
this makes up the structure of a ribosome.
Translation (Protein Synthesis)
1. mRNA leaves the nucleus and enters the cytosol.
2. mRNA attaches to a ribosome.
3. At the start codon (AUG), a tRNA brings its amino
acid into position.
4. Adjacent amino acids bond together with a peptide
bond and the tRNA leaves.
5. The ribosome then moves onto the next codon.
6. This process continues until the STOP codon is
reached.
7. The new protein is released.
Draw the translation process
•
DNA code
•
mRNA codon
•
tRNA anticodon _____________
________________
•
Amino acid
______________
TGA
_____________
____________
______________
_______________
UCU
_______________
_______________
tryptophan
•
DNA code
•
mRNA codon
•
tRNA anticodon _____________
________________
•
Amino acid
______________
CAT
_____________
____________
______________
_______________
GUU
_______________
_______________
methionine