Transcript Nucleic Acids

Nucleic Acids
Deoxyribonucleic Acid (DNA)
Ribonucleic Acid (RNA)
Animal Cell
Bacterial Cell
Nucleic Acids
Nucleic acids allow organisms to transfer genetic information from
one generation to the next.
There are two types of nucleic acids: deoxyribonucleic acid better
known as DNA and ribonucleic acid, better known as RNA.
When a cell divides, its DNA is copied and passed from one cell
generation to the next generation.
DNA contains the "programmatic instructions" for cellular activities.
When organisms produce offspring, these instructions, in the form of
DNA, are passed down.
RNA is involved in the synthesis of proteins. "Information" is typically
passed from DNA to RNA to the resulting proteins
Points to Remember
DNA is present in the nucleus of
eukaryotes and nucleoid of prokaryotes.
RNA is present in the cytoplasm outside
the nucleus.
Ribosomes are the place where proteins
are synthesized.
DNA
The double-stranded chemical instruction
manual for everything a plant or animal
does: grow, divide, even when and how to
die. Very stable, has error detection and
repair mechanisms. Stays in the cell
nucleus. Can make good copies of itself.
Ribonucleic Acid
Messenger RNA is RNA that carries information
from DNA to the ribosome sites of protein
synthesis in the cell.
Ribosomal RNA is the catalytic component of the
ribosomes, the protein synthesis factories in the
cell.
Transfer RNA is a small RNA chain of about 7495 nucleotides that transfers a specific amino
acid to a growing polypeptide chain at the
ribosomal site of protein synthesis, during
translation.
mRNA
Transfer Ribonucleic Acid (tRNA)
Ribosomes
Ribosomes: Message centers throughout
the cell where the information from DNA
arrives in the form of messenger RNA.
The RNA message gets translated into a
form the ribosome can understand and
tells it which protein building blocks it
needs and in what order to assemble
them. Ribosomal RNA helps the
translation go smoothly.
Structure of Ribosome
Deoxyribonucleic Acid
Composition of Nucleic Acids
Nucleic acids are composed of nucleotide
monomers called nucleotides.
Nucleotides have three parts:
A Nitrogenous Base (purine or pyrimidine)
A Five-Carbon Sugar
A Phosphate Group
Nitrogenous Bases
Sugars
Chemical Composition of DNA
The polymeric
structure of DNA may
be described in terms
of monomeric units of
increasing complexity.
Names of DNA Base Derivatives
Base
Nucleosides
5’-Nucleotide
Adenine
2'-Deoxyadenosine
2'-Deoxyadenosine-5'monophosphate
Guanine
2'-Deoxyguanosine
2'-Deoxyguanosine-5'-
monophosphate
Thymine
2'-Deoxythymidine
2'-Deoxythymidine-5'monophosphate
Cytosine
2'-Deoxycytidine
2'-Deoxycytidine-5'monophosphate
A Section of DNA Chain
Base pairing in DNA
Structure of DNA
Chargaff’s Rule
Views about the role of DNA in inheritance
changed in the late 1940's and early 1950's. By
conducting a careful analysis of DNA from many
sources, Erwin Chargaff found its composition to
be species specific. In addition, he found that the
amount of adenine (A) always equaled the
amount of thymine (T), and the amount of
guanine (G) always equaled the amount of
cytosine (C), regardless of the DNA source. As
set forth in the following table, the ratio of (A+T)
to (C+G) varied from 2.70 to 0.35.
How the information of DNA is
Used
Information is stored or encoded in the DNA
polymer by the pattern in which the four
nucleotides are arranged.
To access this information the pattern must be
"read" in a linear fashion, just as a bar code is
read at a supermarket checkout.
Because living organisms are extremely
complex, a correspondingly large amount of
information related to this complexity must be
stored in the DNA. Consequently, the DNA itself
must be very large, as noted above.
How the information of DNA is
Used
In addition to its role as a stable informational
library, chromosomal DNA must be structured or
organized in such a way that the chemical
machinery of the cell will have easy access to
that information, in order to make important
molecules such as polypeptides.
Furthermore, accurate copies of the DNA code
must be created as cells divide, with the
replicated DNA molecules passed on to
subsequent cell generations, as well as to
progeny of the organism.
DNA Organization
Length of DNA
DNA- Function
The genetic information stored in DNA molecules is used as a
blueprint for making proteins. Why proteins? Because these
macromolecules have diverse primary, secondary and tertiary
structures that equip them to carry out the numerous functions
necessary to maintain a living organism
Functions of protein include
• Structural integrity (hair, horn, eye lenses etc.).
• Molecular recognition and signaling (antibodies and hormones).
• Catalysis of reactions (enzymes).
• Molecular transport (hemoglobin transports oxygen).
• Movement (pumps and motors).
Genes
Early geneticists identified genes as hereditary
units that determined the appearance and / or
function of an organism (i.e. its phenotype).
We now define genes as sequences of DNA that
occupy specific locations on a chromosome.
The intriguing question of how the information
encoded in DNA is converted to the actual
construction of a specific polypeptide has been
the subject of numerous studies, which have
created the modern field of Molecular Biology.
DNA Organization
Simple Analogy Between A Chromosome &
Floppy Disk
Genes are stored as sections of
nucleotides along the twisted, doublestranded DNA ladder which makes up
each chromatid. In a sense, genes are like
information files stored on the magnetic
layer of a floppy disk. In this example, the
entire chromosome could be compared
with a floppy disk or CD.
Chromosomes & Floppy Compared
Differences between DNA and RNA
All these RNA's have similar constitutions, and differ from DNA in
two important respects.
As shown in the following diagram, the sugar component of RNA is
ribose, and the pyrimidine base uracil replaces the thymine base of
DNA.
The RNA's play a vital role in the transfer of information
(transcription) from the DNA library to the protein factories called
ribosomes, and in the interpretation of that information (translation)
for the synthesis of specific polypeptides.
Differences between DNA and RNA
Central Dogma of Molecular Biology
The Central Dogma of molecular biology, was
formulated as a simple linear progression of information
from DNA to RNA to Protein.
The replication process consists of passing information
from a parent DNA molecule to daughter molecules.
The transcription process copies this information to a
mRNA molecule.
Finally, this information is used by the chemical
machinery of the ribosome to make polypeptides.
Central Dogma
Protein Synthesis- Transcription
In the first step of protein synthesis, the 2
DNA strands in a gene that codes for a
protein unzip from each other. Similar to
the way DNA replicates itself, a single
strand of messenger RNA (mRNA) is then
made by pairing up mRNA bases with the
exposed DNA nucleotide bases
Protein Synthesis- Translation
After the mRNA is manufactured, it leaves the cell nucleus
and travels to a cellular organelle called the ribosome.
In the ribosome, the mRNA code is translated into a
transfer RNA (tRNA) code which, in turn, is transfered
into a protein sequence.
In this process, each set of 3 mRNA bases (the mRNA
base triplet is called a codon) will pair with a
complimentary tRNA base triplet (called an anticodon).
Each tRNA is specific to an amino acid, as tRNA's are
added to the sequence, amino acids are linked together
by peptide bonds, eventually forming a protein that is
later released by the tRNA.
Protein Synthesis
Protein
The amino acid chain then folds into a
specific protein (myoglobin).
Posttranslational Modifications
Most secretory proteins are secreted as
precursors called preprotein eg collagen is
secreted as preprocollagen.
Preprocollagen contains a leader sequence
which directs it into the endoplasmic reticulum
where it is enzymatically removed.
The procollagen molecule contains polypeptide
extensions at both amino and carboxyl terminals
neither of which id present in mature collagen.
Preprocollagen
Genetic Code
Genetic Code
From Gene to Protein
Orphan Gene
An orphan gene is a gene that has limited
phylogenetic distribution.
There is no detectable homolog in other
organisms or the homologous genes are
restricted to closely-related organisms.
Orphan gene clusters are sections of DNA
for which scientists cannot determine what
is ultimately produced