DNA and Protein Synthesis

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DNA and Protein Synthesis
Chromosomes are tightly coiled bodies in the
nuclei of eukaryotic cells, made of
deoxyribonucleic acid wrapped around proteins
called histones.
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A gene is a segment of DNA that contains the
instructions for making a particular polypeptide
or RNA molecule.
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There are 2 kinds of nuclei acids DNA and RNA

• There are 4 types of ribonucleic acid
• messenger RNA mRNA
• transfer RNA tRNA
• ribosomal RNA rRNA
• small nuclear RNAs

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DNA is a double polymer made of smaller monomer
subunits called nucleotides.

• Each nucleotide is composed of 3 parts
• A nitrogen containing organic base
• A 5-carbon sugar
• A phosphate group

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Lets draw 2 DNA nucleotides.
HO
H
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All deoxyribonucleic acid is made from the same 4
nucleotides

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2 complementary nitrogenous bases
Alternating sugar phsosphate groups form the
backbone.
glycosidic bond
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Human DNA is a ladder 3.2 billion nucleotides
long.
The DNA double helix spiral staircase twisted
ladder
The two strands are antiparallel.
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James Watson Frances Crick
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Rosalind Franklin took x-ray diffraction pictures
of DNA molecules.
May 2, 1952
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Any time cells divide, DNA molecules must make
exact copies of themselves. This process is
called replication.
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• When cells divide for growth, wound repair,
  asexual reproduction, or to replace worn out
  cells, the DNA must replicate so new daughter
  cells have the same genetic code as the parent
  cell.

Minutes after fertilization
Sea urchin early embryo development
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What does the code on DNA control?
What is the source of the nucleotides needed for
DNA replication?
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From DNA to RNA to Protein
The central dogma of molecular biology is that
the flow of genetic information in cells is from
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RNA is single stranded, but can fold into
3-dimensional shapes. DNA is doubled
stranded.
DNA
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mRNA is one gene long. Each DNA molecule is many
genes long.
DNA stays in the nucleus.
mRNA
to cytoplasm
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stop sequence
Transcription is the process of mRNA copying the
code on the DNA.
U
U
U
RNA polymerase continues until a stop sequence is
reached.
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How the DNA code is translated into protein

• There are 4 different nucleotides in DNA.
• There are 20 different amino acids in proteins.
• How many nucleotides does it take to code for one
  amino acid?

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These groups of 3 bases are called triplets on
the DNA and triplet codons on the mRNA.
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5 AUG CUC GUU ACA UGA 3
The genetic code is redundant.
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Eukaryotic genes have many long noncoding
sequences called introns that must be snipped out
of the primary transcript that becomes mRNA.
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• Transcription in eukaryotes occurs in the
  nucleus.
• The mature mRNA leaves through nuclear pores.

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About 13 of our DNA is transcribed, but only 2
4 is translated into polypeptides.
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transfer RNA
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Translation is the process of tRNAs placing amino
acids in the correct order by matching anticodon
to codon on the mRNA.
Translation
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What determines an organisms appearance and
?behavior?

• The proteins that the organism makes.
• The order of the nitrogenous bases in the
  organisms DNA.

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What body parts or substances are proteins?

• Enzymes
• Muscle fibers
• Some hormones
• Functional pigments melanin, chlorophyll,
  hemoglobin
• Transmembrane proteins
• Cytoskeleton microfilaments, microtubules
• Hair, nails

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Transcription of a gene to make mRNA
DNA template side
T A C G C A C A G C C G T C G A C T G G T C A G
T A A A C T _____________________________________
__________________________________ _____________
__________________________________________________
________
U G A
A U U
A G C
G U C
C C A
U G A
G G C
A U G
G U C
C G U
A T G C G T G T C G G C A G C T G A C C A G T C
A T T T G A
Other side of DNA
Primary transcript RNA
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Translation on a Ribosome
Met
Val
Pro
Val
Arg
RF
_________________________________________________
__ mRNA
A U G
C G U
G U C
C C A
G U C
U G A
Ribosome
RF release factor
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DETERMINING THE DNA CODE GIVEN THE AMINO ACID
SEQUENCE OF A POLYPEPTIDE
Met Ala Pro Val Lys Trp Gly Ser
STOP
UAC
ACC
CCA
AGA
CGA
GGA
CAA
UUU
AUG
GCU
CCU
GUU
AAA
UGG
GGU
UCU
UAG
mRNA codons
tRNA anticodons
GGA
CAA
TAC
CGA
TTT
ACC
CCA
AGA
ATC
DNA template
Undoubtedly wrong?