STRAND 2 – LIFE AT THE MOLECULAR, CELLULAR AND TISSUE
LEVEL
1. Nucleic Acids
1. Definition: Organic molecules that control the synthesis of protein in all
living cells by storing and transferring genetic information.
2. Historical Perspective:
o 1953: James Watson and Francis Crick published a paper describing the
structure of Nucleic Acids; received Nobel prizes.
o Rosalind Franklin laid the foundation for their discovery by developing X-
ray technology that allowed Watson & Crick to view the helical nature of
DNA – never officially recognized.
o In the next decade, Watson & Crick discovered how nucleic acids control
protein synthesis in cells.
3. Structure:
1. 5-Carbon pentose (sugar)
2. Phosphate group
3. Nitrogenous base
DNA RNA
Double helix structure Single stranded
Deoxyribose sugar Ribose sugar
AGCT AGCU
Equal number of nitrogenous bases Nitrogenous bases occur in any
ratio/sequence/number
o Purine Bases – Adenine & Guanine
o Pyrimidine Bases – Cytosine & Thymine (Uracil)
Sequence in which nucleotides are arranged will differ amongst organisms
and leads to variety
Nitrogenous bases are held
together by weak Hydrogen bonds
(A=T; G≡C)
Nitrogenous base and sugar
molecule is held together by an
ester bond
Phosphate and sugar molecule is
held together by a glycosidic
bond
1
, Both an ester and glycosidic bond require a condensation reaction to take place.
Condensation Reaction:
o Occurs when 2 molecules join to form a larger molecule (polymer), and
releases water in the process.
o Dehydration reaction: nucleotides link together to form a long chain with a
backbone of alternating sugar and phosphate groups. (Strands are anti-
parallel).
4. DNA – Deoxyribonucleic Acid
o Nitrogenous Bases: AGCT
a. Watson-Crick Model:
DNA molecule consists of 2 polynucleotide chains linked together &
twisted around each other to form a double helix structure
Nitrogenous base pairs form rungs of ‘ladder’
b. Functions:
1. Stores the sequence of nitrogenous bases unique to each species (this is
the genetic code)
2. Controls the synthesis of RNA
3. Controls the structure & function of cell by dictating protein synthesis
c. DNA Replication
1) Double helix structure of DNA unwinds
2) 2 strands appear in shape of ladder
3) Weak H-bonds break and 2 strands ‘unzip’
4) Free-floating nucleotides in nucleoplasm build a complimentary DNA
strand onto each of the original DNA strands
5) DNA polymerase controls the joining of nucleotides
o Each original DNA strand will serve as a template strand
6) 2 new strands rewind to form helix structure
7) New double helix winds itself around histones
8) New DNA molecules contract and become shorter/thicker to form 2
chromosomes of new cell
Importance of DNA Replication before Mitosis: Ensures each daughter cell
contains the same genetic information as the mother cell.
d. Mitochondrial DNA (mtDNA)
o Contributed by ovum during fertilization
o Inherited by both male and female offspring through maternal line
o Rarely mutates and therefore reliable when determining relatedness along
maternal line
o Genes for mtDNA code for enzymes that control cellular respiration
2
LEVEL
1. Nucleic Acids
1. Definition: Organic molecules that control the synthesis of protein in all
living cells by storing and transferring genetic information.
2. Historical Perspective:
o 1953: James Watson and Francis Crick published a paper describing the
structure of Nucleic Acids; received Nobel prizes.
o Rosalind Franklin laid the foundation for their discovery by developing X-
ray technology that allowed Watson & Crick to view the helical nature of
DNA – never officially recognized.
o In the next decade, Watson & Crick discovered how nucleic acids control
protein synthesis in cells.
3. Structure:
1. 5-Carbon pentose (sugar)
2. Phosphate group
3. Nitrogenous base
DNA RNA
Double helix structure Single stranded
Deoxyribose sugar Ribose sugar
AGCT AGCU
Equal number of nitrogenous bases Nitrogenous bases occur in any
ratio/sequence/number
o Purine Bases – Adenine & Guanine
o Pyrimidine Bases – Cytosine & Thymine (Uracil)
Sequence in which nucleotides are arranged will differ amongst organisms
and leads to variety
Nitrogenous bases are held
together by weak Hydrogen bonds
(A=T; G≡C)
Nitrogenous base and sugar
molecule is held together by an
ester bond
Phosphate and sugar molecule is
held together by a glycosidic
bond
1
, Both an ester and glycosidic bond require a condensation reaction to take place.
Condensation Reaction:
o Occurs when 2 molecules join to form a larger molecule (polymer), and
releases water in the process.
o Dehydration reaction: nucleotides link together to form a long chain with a
backbone of alternating sugar and phosphate groups. (Strands are anti-
parallel).
4. DNA – Deoxyribonucleic Acid
o Nitrogenous Bases: AGCT
a. Watson-Crick Model:
DNA molecule consists of 2 polynucleotide chains linked together &
twisted around each other to form a double helix structure
Nitrogenous base pairs form rungs of ‘ladder’
b. Functions:
1. Stores the sequence of nitrogenous bases unique to each species (this is
the genetic code)
2. Controls the synthesis of RNA
3. Controls the structure & function of cell by dictating protein synthesis
c. DNA Replication
1) Double helix structure of DNA unwinds
2) 2 strands appear in shape of ladder
3) Weak H-bonds break and 2 strands ‘unzip’
4) Free-floating nucleotides in nucleoplasm build a complimentary DNA
strand onto each of the original DNA strands
5) DNA polymerase controls the joining of nucleotides
o Each original DNA strand will serve as a template strand
6) 2 new strands rewind to form helix structure
7) New double helix winds itself around histones
8) New DNA molecules contract and become shorter/thicker to form 2
chromosomes of new cell
Importance of DNA Replication before Mitosis: Ensures each daughter cell
contains the same genetic information as the mother cell.
d. Mitochondrial DNA (mtDNA)
o Contributed by ovum during fertilization
o Inherited by both male and female offspring through maternal line
o Rarely mutates and therefore reliable when determining relatedness along
maternal line
o Genes for mtDNA code for enzymes that control cellular respiration
2
