DNA, RNA AND PROTEIN SYNTHESIS
DNA (DEOXYRIBONUCLEIC ACID)
• Nucleic acid that composes chromosomes and
carries genetic information.
CHROMOSOME ORGANIZATION
1. A chromosome is an enormous strand of super
coiled DNA.
2. Sections of DNA on the chromosome that code
for proteins are called genes.
3. Noncoding sections of DNA are called “junk
DNA” (regulatory or unknown function)
BUILDING BLOCKS OF DNA
Composed of nucleotides
• Nucleotides contain three parts:
1. 5-Carbon Sugar (deoxyribose)
2. Phosphate Group
3. Nitrogen Base (four types, adenine,
guanine, thymine and cytosine)
• Adenine and Guanine are purines
(composed of two rings of nitrogen atoms)
• Thymine and Cytosine are pyrimidines
(composed of one ring of nitrogen atoms)
STRUCTURE OF DNA
• Consists of two strands of nucleotides that
form a twisted ladder (double helix)
• Sugar and phosphate alternate along the
sides of the ladder (linked by strong
covalent bonds)
• Pairs of nitrogen bases form the rungs of
the ladder (linked by weak hydrogen
bonds).
• Specific base pairing arrangement
A-T : 2 hydrogen bonds
C-G : 3 hydrogen bonds
• Nitrogen bases attach to the sugar portion
of the side (NOT the phosphate)
• Strands run in opposite directions
FUNCTION OF DNA
• DNA codes for proteins (structural
proteins, enzymes, and hormones)
• information for building proteins is carried
in the sequence of nitrogen bases
• proteins determine physical and metabolic
traits and regulate growth and
development.
DNA REPLICATION
Process in which DNA is copied
PURPOSE OF DNA REPLICATION
Gives daughter cells produced by cell
division a complete set of genetic
information identical to the parent cell.
WHERE DNA REPLICATION OCCURS
Nucleus
WHEN DURING THE CELL CYCLE DOES
REPLICATION OCCUR?
Interphase
HOW REPLICATION OCCURS
1. Helicase enzymes unzip the parent strand by separating
the nitrogen base pairs. (The Unzipper)
2. DNA polymerase pairs free DNA nucleotides with the
exposed bases on both strands following the base pair
rules. (The Builder)
– each strand from the parent molecule serve as a template
3. Primase (The Initializer) Makes the primer to
polymerase knows where to go. Piece of RNA
4. Ligase (The Gluer) Helps glue DNA fragments together
5. Hydrogen bonds reform spontaneously sealing the two
strands of each DNA molecule together
Amoeba Sisters Video at minute 2:00-3:22. Take notes on the 4 DNA
Replication Characters and Job
RESULTS OF REPLICATION
• Two molecules of DNA that are identical
• Each is half old (strand from parent) and half new (strand
synthesized by DNA polymerase)
RNA (RIBONUCLEIC ACID)
Nucleic acid involved in the synthesis
of proteins
RNA STRUCTURE
Composed of nucleotides, but differs from
DNA in three ways.
1.
2.
3.
Single strand of nucleotides instead of double stranded
Has uracil instead of thymine
Contains ribose instead of deoxyribose
RNA FUNCTION
Three forms of RNA involved in protein synthesis
1. mRNA (messenger): copies instructions in DNA and
carries these to the ribosome.
2. tRNA (transfer): carries amino acids to the ribosome.
3. rRNA (ribosomal): composes the ribosome.
PROTEIN SYNTHESIS
Cells build proteins following instructions
coded in genes (DNA).
• Consists of two parts, transcription and
translation
TRANSCRIPTION
DNA is copied into a complementary strand of mRNA.
WHY?
• DNA cannot leave the nucleus. Proteins are made in the
cytoplasm. mRNA serves as a “messenger” and carries the
protein building instructions to the ribosomes in the
cytoplasm.
LOCATION OF TRANSCRIPTION
Nucleus
RESULT OF TRANSCRIPTION
mRNA strand with instructions for building a
protein leaves the nucleus and goes to the
cytoplasm.
TRANSCRIPTION EXAMPLE
Transcribe the following DNA Sequence in
mRNA
DNA
RNA
TAC CGG ATC CTA GGA TCA
AUG GCC UAG GAU CCU AGU
PROTEINS
Structural and functional components of
organisms.
• Composed of amino acids (20)
• Order of nucleotides in DNA determines
order of amino acids in a protein
• One gene codes for one protein
GENETIC CODE
The “language” that translates the sequence
of nitrogen bases in DNA (mRNA) into the
amino acids of a protein.
• Codon = three nucleotides on DNA or
mRNA
• One codon specifies one amino acid
• The genetic code is universal to all
organisms
TRANSLATION
Instructions in mRNA are used to build a protein
LOCATION OF TRANSLATION
ribosome (in the cytoplasm)
• PROCESS OF TRANSLATION
RNA is transcribed in the nucleus. As a single strand, it
is able to leave through the pores of the nucleus and
move to the cytoplasm.
mRNA (messenger RNA) carries the code for the
assembly of proteins to the ribosomes which are located
throughout the cytoplasm.
The mRNA is held in place on the ribosomes. tRNA
(transfer RNA) picks up amino acids which are spread
throughout the cytoplasm and brings them to the mRNA
on the ribosomes. There the assembly of proteins is
completed.
RESULT OF TRANSLATION
A Protein!
Codon Video