BIOL 150 Chapter Notes - Chapter 3: Small Interfering Rna, Exon, Frederick Griffith
Chapter 3: Nucleic Acids and Transcription
➔Deoxyribonucleic acid (DNA)- a linear polymer of 4 different subunits.
◆DNA molecules from all cells and organisms have a very similar 3D structure,
reflecting their shared ancestry.
●Double helix- composed of two strands coiled around each other to form a
sort of spiral staircase.
○Banisters of the spiral staircase are formed by the linear backbone
of the paired strands, steps are formed by the pairing of the
subunits at the same level in each strand.
◆Staircase structure is common to all cellular DNA molecules, structure gives clues
to its functions.
●(1) DNA stores information.
○Some of the information in DNA encodes for proteins and provide
structure and do much of the work of the cell.
○Genetic information- information in the DNA, organized in the
form of genes- as textual information is organized in the form of
words.
◆Genes can exist in different forms in different individuals,
even within a single species.
◆Genes usually have no effect on the organism unless they
are “turned on” and their product is made.
●Turning on of a gene- gene expression.
◆Gene regulation- the molecular processes that control
whether gene expression occurs at a given time or in a
given cell.
●(2) DNA transmits
genetic information from one generation to the next.
○The transmission of genetic information from parents to the
offspring enables species of organisms to maintain their identity
through time.
○The genetic information in DNA guides the development of the
offspring, ensuring that parental apple trees give rise to apple
seedlings and parental geese give rise to goslings.
3.1 MAJOR BIOLOGICAL FUNCTIONS OF DNA
➔DNA is the molecule by which hereditary information is transmitted from generation to
generation.
◆Highly diverse.
➔Proteins carry out most of the essential activities in the life of cell, logical that they play
role in heredity.
DNA can transfer biological characteristics from one organism to another.
➔Frederick Griffith, 1928, experiment working with the bacterium Streptococcus
pneumoniae.
◆Organism causes a variety of infections in humans and a deadly form of
pneumonia in mice.
◆Griffith studied two strains of the bacterium, one harmful and one non harmful.
➔Experiments in 1944 by Oswald Avery, Colin MacLeod, and Maclyn McCarty.
◆Showed that the molecule responsible for the transformation of nonvirulent cells
into virulent cells is DNA.
◆This experiment along with other, established that DNA is the genetic material.
◆Today, transformation is widely used in biological research and in the genetic
modification of agricultural plants and animals.
DNA molecules are copied in the process of replication.
➔DNA can serve as the genetic material because it is unique among cellular molecules in
being able to specify exact copies of itself.
➔Replication: the copying process, allows the genetic information from one DNA
molecules to be copied into that of another DNA molecule.
◆Faithful replication is critical in that it allows DNA to pass genetic information
from cell to cell and from parent to offspring.
◆The copying must reproduce the sequence of subunits almost exactly because
mistakes in DNA replication that go unrepaired may be harmful to the cell or
organism.
◆Mutation: An unpaired error in DNA replication, a change in the genetic
information in DNA.
●Rare favorable mutations are essential in the process of evolution.
○They allow populations of organisms to change through time and
adapt to their environment.
Genetic information flows from DNA to RNA to protein.
➔Biologists often say that genetic information in DNA directs the activities in a cell or
guides the development of an organism, but these effects of DNA are indirect.
◆Most of the active molecules in cells and development are proteins, including the
enzymes that convert energy into usable forms and the proteins that provide
structural support of the cell.
◆DNA acts indirectly by specifying the sequence of amino acid subunits of which
each protein is composed.
◆Sequence in turn determines the 3D structure of the protein, its chemical
properties, and its biological activities.
➔In specifying the amino acid sequence of proteins, DNA acts through an intermediary
molecule, ribonucleic acid (RNA), another type of polymer.
➔Central dogma- the flow of information from DNA to RNA to protein,
◆States that genetic information can be transferred from DNA to RNA to protein.
●Some expectations have been discovered.
○The transfer of genetic information from RNA to DNA (HIV,
causes AIDS).
○RNA to RNA (in replication of the genetic material of influenza
virus).
○Protein to protein (in the unusual case of disease-causing
molecules-prions).
➔1st step in the process- Transcription: the genetic information in a molecule of DNA is
used as a template, to generate a molecule of RNA.
◆This term is used because it emphasizes that both molecules use the same
language of nucleic acids.
◆It is the first step in gene expression- production of a functional gene product.
➔2nd step- translation: a molecules of RNA is used as a code for the sequence of amino
acids in a protein.
◆This term is used to indicate a change of languages, from nucleotides that make
up nucleic acids to amino acids that make up proteins.
➔Processes of transcription and translation are regulated- they do not occur at all times in
all cells, even though cells in an individual contain the same DNA.
◆Genes are expressed, “turned off”, only at certain times and places, and not
expressed at other times or places.
◆In multicellular organisms, cells are specialized for certain functions, these
different functions depend on which genes are on and which genes are off in
specific cells.
●Muscle cells express genes that encode for proteins involved in muscle
contraction, but these genes are not expressed in skin cells or liver cells for
example.
●During development of a multicellular organism, genes may be required at
certain times but not at others.
○In this case, timing of expression is carefully controlled.
➔In prokaryotes, transcription and translation occur in the cytoplasm, in eukaryotes the two
processes are separated from each other, with transcription occurring in the nucleus and
translation in the cytoplasm.
◆Separation of transcription and translation in time and space in eukaryotic cells
allows for additional levels of gene regulation that are not possible in prokaryotic
cells.
◆Despite their differences, the processes are sufficiently similar that they must have
evolved early in the history of life.
3.2 CHEMICAL COMPOSITION AND STRUCTURE OF DNA
Document Summary
Deoxyribonucleic acid (dna) - a linear polymer of 4 different subunits. Dna molecules from all cells and organisms have a very similar 3d structure, reflecting their shared ancestry. Double helix - composed of two strands coiled around each other to form a. Banisters of the spiral staircase are formed by the linear backbone sort of spiral staircase. of the paired strands, steps are formed by the pairing of the subunits at the same level in each strand. Staircase structure is common to all cellular dna molecules, structure gives clues to its functions. Some of the information in dna encodes for proteins and provide structure and do much of the work of the cell. Genetic information - information in the dna, organized in the form of genes - as textual information is organized in the form of words. Genes can exist in different forms in different individuals, even within a single species.
