DNA:
Nucleic Acids and Protein Synthesis
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DNA Structure and Replication
What is DNA?
• DNA stands for deoxyribonucleic acid
• DNA determines the traits of organisms by
determining the structure of proteins.
– Think of it as a “blueprint”.
• The proteins carry out all of the work in the cell
and essentially carry out all of the actions of life!
– Remember: Ribosomes make proteins!
Where Do I Find DNA?
• Chromosomes are in the
nucleus of every cell.
• Chromosomes are made
up of DNA.
• Genes are pieces of DNA
that contain the instructions
for building a protein.
The Structure of Nucleotides
• DNA is made up of repeating nucleotide
subunits.
• One nucleotide = phosphate group, sugar
(deoxyribose), and one of four nitrogenous
bases
The Structure of Nucleotides
• The four nitrogenous bases ultimately give the
nucleotide its “identity”
– Adenine (A)
– Thymine (T)
– Cytosine (C)
– Guanine (G)
Purines- A, G
Pyrimidines- T, C
The Structure of DNA
• DNA is made up of two strands of nucleotides
coiled up into a double helix or “twisted
ladder” shape
• The sugar and phosphate
creates the backbone of
the DNA molecule
The Structure of DNA
• The bases attach to the sugar on the DNA
molecule and base pair to a partner with a
hydrogen bond. This creates the “rungs” of the
twisted ladder.
• The bases of one nucleotide strand will base pair
to the bases on the other nucleotide strand
– A always pairs with T
– C always pairs with G
The Structure of DNA
T pairs with A
C pairs with G
Sugar and phosphate
forms the “backbone”
Order of the bases holds
the information
The Importance of Nucleotide
Sequences
• The order of the bases holds the genetic
information as a “code”
– Just like the letters of the alphabet make up words!
• Example: ATTGAC means something completely
different than TCCAAA
• The more similar two organisms’ DNA sequences
are, the more related the organisms are!
DNA Replication
• All new cells (made by mitosis and meiosis) need
a complete copy of the DNA
– This is completed during S phase of Interphase
• DNA must be copied so each cell can have its own
copy.
– This process is called DNA replication.
semiconservative replication – the process in which the
DNA molecule uncoils and separates into two strands.
Each original strand becomes a template on which a
new strand is constructed, resulting in two DNA
molecules identical to the original DNA molecule.
How DNA replicates
1. Enzyme breaks the bonds between the bases that
holds the two strands together. This is called
“unzipping” the DNA.
2. Another enzyme (DNA polymerase) assembles a
complementary nucleotide chain for each original
nucleotide strand. The newly added nucleotide
strand is called the complementary strand.
3. At the end you are left with two identical copies of
the DNA.
DNA Replication
Practice DNA Replication
1.) A T T G C T A G
T A A C G A T C
2.) G C T A T C G A C
3.) A G C T A C A A T C C A
Gene to Protein
Gene to Protein
The Central Dogma
RNA
• RNA and DNA are both nucleic acids that are made out
of nucleotides
• Three main differences:
– RNA is single stranded;
DNA is double stranded
– RNA’s sugar is ribose;
DNA’s sugar is deoxyribose
– RNA contains uracil (U);
DNA contains thymine (T)
Types of RNA
• There are three main types of RNA that carry
out important roles in the cell:
1. mRNA – brings instructions from the DNA in
the nucleus to the cytoplasm
2. rRNA – makes up part of the ribosome
3. tRNA – brings amino acids to the ribosome to
build proteins
Transcription
-The process in which a strand of mRNA is synthesized by
using the genetic information found on a strand of DNA as a
template.
-RNA polymerase reads the complementary DNA strand and
attaches complementary RNA bases.
• Occurs in the nucleus
• An RNA copy of a portion of DNA is made
• Happens similar to replication except:
–
–
–
–
One strand of RNA (single-stranded) is made
RNA polymerase is the enzyme that carries out transcription
A pairs with U (rather than T)
G pairs with C
Practice Transcription
Complementary/non-coding
DNA strand -
T A C G G A C T G A T T
mRNA strand - A U G C C U G A C U A A
Translation
-the process in which the mRNA molecules is
decoded to produce a sequence of amino
acids for protein synthesis
– mRNA is read in codons (groups of 3 bases)
– Each codon has a particular amino acid that goes
with it
– The genetic code is universal; all organisms use
the same code
Translation
• Occurs on the ribosomes in the cytoplasm
• mRNA is “read” by the ribosomes (either “free” in the cytoplasm or
on the rough endoplasmic reticulum) and tRNA molecules bring
amino acids to the ribosome to be assembled into a polypeptide
chain
• Rough ER is responsible for transporting the newly synthesized
proteins to the Golgi apparatus where carbohydrates are added to
it and it is packaged in a vesicle for transportation to the cell
membrane.
polypeptide chain- chain of amino acids joined together by peptide
bonds
• proteins are polypeptide chains folded into specific shapes
Translation
Write in the 3-letter code in your
handbok on page 12!!!!
Practice Reading the Genetic Code
• What amino acid is coded for by the following
codons?
– CCC
– GUA
– AUC
– AUG
– UAA
Proline (Pro)
Valine (Val)
Isoleucine (Ile)
Methionine (Met)/ Start
Stop
• What codons stand for serine?
UCU, UCC, UCA, UCG, AGU, AGC,
Practice Transcription and Translation
Using the following DNA sequence, transcribe it into
mRNA and then translate it into an amino acid sequence:
Coding DNA: A T G T T T A C C T A T G A C T A A
Complementary DNA:
T A C A A A T GG AT A C T G A T T
mRNA: A U G U U U A C C U A U G A C U A A
amino acid sequence :
Met Phe Thr Tyr Asp Stop