,LIFE AT THE MOLECULAR, CELLULAR AND TISSUE LEVEL
UNIT 1 - DNA
Nucleus Revision
Contains pores that form passage
between the nucleus and cytoplasm
Small round body
Mass of thread-like structures and
when cell divides, the chromatin
network coils and thickens into
separate and shorter threads
known as chromosomes which carry
Encloses nuclear membrane and is a jelly-like liquid the genetic material of the cell
Functions:
• Chromosomes in the nucleus store the genetic material of the cell
• Nucleus regulates the structure and metabolism of the cell
Deoxyribose Acid ( DNA )
Location
• Chromosomal DNA —> DNA that occurs in nucleus and forms part of chromatin network ( chromosomes )
• Extranuclear DNA ( outside nucleus ) —> mitochondria of plants and chloroplasts
• Mitochondrial DNA
• Found in mitochondria and is passes from mother to child and thus traced in maternal lines and remains
unaltered
• Shorter and Circular in shape
• Determines relatedness and can’t be passed down the paternal line as the mitochondrial DNA occurs at the base
of the sperm tail which then detaches as it enters the ovum so the only DNA left is in the ovum
• Endosymbiosis —> proposes origin of mitochondria. Bacteria entered as a single cell as a prey or parasite that
avoided digestion and became an independent organelle containing its own DNA
• The more mtDNA corresponds, the more closely related organisms are to one another
Chromosomes and Genes Discovery of Structure ( James Watson and Francis Crick )
• Chromosomes —> long, thin, • Early 1950’s —> both became involved in DNA research and only knew
thread-like structures that the genetic material was DNA but the structure was still unknown
composed of DNA that is • Chargaff’s discovery about equal numbers of adenine and thymine and
wrapped around proteins guanine and cytosine bases is all that was known while Maurice Wilkins
called Histones and Rosalind Franklin were also doing DNA research
• Gene —> short segment of • 1952 —> X-ray photos were taken and Franklin summarized that it was a
DNA molecule that codes for helix shape but Wilkin showed the X-ray to Crick without Franklin’s
a particular protein ( carries permission
the code and the proteins • Watson and Cricked used it to create a 3D model structure and described
determines the in a scientific article and along with Wilken’s they collectively received a
characteristics of an noble price for their discovery while Franklin died of cancer in 1958 age
organisms ) 37
,Structure
• Giant molecule that consists of 2 strands that form a double helix ( looks like a ladder when unwound )
• DNA is a polymer made up of large number of similar units called monomers ( nucleotides )
Nucleotides:
• Sugar Molecules —> deoxyribose ( D )
• Phosphate Group
• Nitrogenous Base ( 4 types ): Adenine and Guanine are large molecules known as Purine Bases and Cytosine
and Thymine are smaller molecules known as Pyrimidines
Formation:
• The deoxyribose of one nucleotide forms a bond with the phosphate group of another and two long strands
are formed
• The sides of the ladder consist of alternating deoxyribose molecules and phosphate group
• Each rung of the DNA ladder is formed by linking the 2 nitrogenous bases by pairing one small pyrimidine
with a large purine creating a base pair
• The bases are bonded by weak hydrogen bonds which are
easily broken by enzyme action
• Two hydrogen bonds formed between A and T and three
form between G and C and there will always be equal
amount of bases
• Each nucleotide may be repeated in the DNA strand and
base pairs occur in any sequence
• The sequence of bases it’s important as it provides the code
that gives instruction for the synthesis of proteins —>
known as the genetic code or code of life
• Each DNA strand is the complement of the other strand
Role of DNA
Genes: Non-Coding DNA
• Carries the genetic code for the synthesis of • 2% of DNA code from proteins
proteins • The rest may be used in DNA fingerprinting/profiling
• Short segment of DNA with a specific sequence ( Polymerase Chain Reaction - technology that replicates
of nitrogenous bases it in test tube to compare. Can help with paternal proof,
• Sequence determines the sequence and the type identifying crime suspects and missing people but can be
of amino acids that will combine to form a used to discriminate and is costly. It is seen as
particular protein confidential and may be used for abuse by government
• DNA can replicate to ensure that the genetic which are some arising ethical issues )
code is accurately transferred from one • Play role in regulation and control of the expression of
generation to the next genes in the coding DNA ( where the genes switch on
and off )
• Protects the gene from mutations and controls the
process of copying gene during transcription ( protein
synthesis )
, DNA Replication
• Replication —> the duplication of the DNA molecule to form 2 identical copies and takes place during
Interphase of the cell cycle
• Proteins ( Histones ), together with DNA form part of a chromosome and also duplicate during replication
( identical units are called chromatids )
• Chromatids are held together by a centromere
Process of Replication:
1. Double helix unwinds into 2 strands
2. Weak hydrogen bonds break and the strands unzip
3. Free-floating nucleotides in nucleoplasm build complementary strand onto each of the original two strands
4. DNA Polymerase join the nucleotides
• Each DNA strand served as a template on which its complement forms and each copy comprised of an ‘old’
and ‘new’ strand and the double-stranded structure is what made the replication possible
• Importance of Replication —> during mitotic cell division, one mother cell divides into 2 identical daughter
cells so it is essential that DNA makes identical copies of itself before cell division in order to ensure each
daughter cell contains the same genetic material as the mother.
Ribonucleic Acid ( RNA )
Location Structure
• Nucleus • Single strand that is a polymer with nucleotides and
• Cytoplasm monomers
• Forms part of Ribosomes
Nucleotides:
Formation: • Sugar Molecule —> Ribose
• Forms a single long strand and the bases • Phosphate Group
occurs in any number and ratio • Nitrogenous Base: Adenine, Guanine, Cytosine and Uracil
Types of RNA
Transfer RNA ( tRNA ) Messenger RNA ( mRNA ) Ribosomal RNA ( rRNA )
• Consists of a single • Single strand with an unlimited number of • Consists of a single strand
strand that folds nucleotides • Forms part of the structure
back on itself and it • Formed in the nucleoplasm, using DNA as a of the ribosomes in the
occurs in the template cytoplasm and plays a role in
cytoplasm • MRNA carries the genetic codes from DNA in the control of protein
• 3 exposed bases, the nucleus to the ribosomes in the synthesis
called the anticodon, cytoplasm and thus acts as a messenger
occur on one of the
loops Differences between DNA and RNA
• tRNA picks up amino
acids in the
cytoplasm and takes
them to the
ribosome where
protein synthesis
occurs and it acts as
a transfer molecule
UNIT 1 - DNA
Nucleus Revision
Contains pores that form passage
between the nucleus and cytoplasm
Small round body
Mass of thread-like structures and
when cell divides, the chromatin
network coils and thickens into
separate and shorter threads
known as chromosomes which carry
Encloses nuclear membrane and is a jelly-like liquid the genetic material of the cell
Functions:
• Chromosomes in the nucleus store the genetic material of the cell
• Nucleus regulates the structure and metabolism of the cell
Deoxyribose Acid ( DNA )
Location
• Chromosomal DNA —> DNA that occurs in nucleus and forms part of chromatin network ( chromosomes )
• Extranuclear DNA ( outside nucleus ) —> mitochondria of plants and chloroplasts
• Mitochondrial DNA
• Found in mitochondria and is passes from mother to child and thus traced in maternal lines and remains
unaltered
• Shorter and Circular in shape
• Determines relatedness and can’t be passed down the paternal line as the mitochondrial DNA occurs at the base
of the sperm tail which then detaches as it enters the ovum so the only DNA left is in the ovum
• Endosymbiosis —> proposes origin of mitochondria. Bacteria entered as a single cell as a prey or parasite that
avoided digestion and became an independent organelle containing its own DNA
• The more mtDNA corresponds, the more closely related organisms are to one another
Chromosomes and Genes Discovery of Structure ( James Watson and Francis Crick )
• Chromosomes —> long, thin, • Early 1950’s —> both became involved in DNA research and only knew
thread-like structures that the genetic material was DNA but the structure was still unknown
composed of DNA that is • Chargaff’s discovery about equal numbers of adenine and thymine and
wrapped around proteins guanine and cytosine bases is all that was known while Maurice Wilkins
called Histones and Rosalind Franklin were also doing DNA research
• Gene —> short segment of • 1952 —> X-ray photos were taken and Franklin summarized that it was a
DNA molecule that codes for helix shape but Wilkin showed the X-ray to Crick without Franklin’s
a particular protein ( carries permission
the code and the proteins • Watson and Cricked used it to create a 3D model structure and described
determines the in a scientific article and along with Wilken’s they collectively received a
characteristics of an noble price for their discovery while Franklin died of cancer in 1958 age
organisms ) 37
,Structure
• Giant molecule that consists of 2 strands that form a double helix ( looks like a ladder when unwound )
• DNA is a polymer made up of large number of similar units called monomers ( nucleotides )
Nucleotides:
• Sugar Molecules —> deoxyribose ( D )
• Phosphate Group
• Nitrogenous Base ( 4 types ): Adenine and Guanine are large molecules known as Purine Bases and Cytosine
and Thymine are smaller molecules known as Pyrimidines
Formation:
• The deoxyribose of one nucleotide forms a bond with the phosphate group of another and two long strands
are formed
• The sides of the ladder consist of alternating deoxyribose molecules and phosphate group
• Each rung of the DNA ladder is formed by linking the 2 nitrogenous bases by pairing one small pyrimidine
with a large purine creating a base pair
• The bases are bonded by weak hydrogen bonds which are
easily broken by enzyme action
• Two hydrogen bonds formed between A and T and three
form between G and C and there will always be equal
amount of bases
• Each nucleotide may be repeated in the DNA strand and
base pairs occur in any sequence
• The sequence of bases it’s important as it provides the code
that gives instruction for the synthesis of proteins —>
known as the genetic code or code of life
• Each DNA strand is the complement of the other strand
Role of DNA
Genes: Non-Coding DNA
• Carries the genetic code for the synthesis of • 2% of DNA code from proteins
proteins • The rest may be used in DNA fingerprinting/profiling
• Short segment of DNA with a specific sequence ( Polymerase Chain Reaction - technology that replicates
of nitrogenous bases it in test tube to compare. Can help with paternal proof,
• Sequence determines the sequence and the type identifying crime suspects and missing people but can be
of amino acids that will combine to form a used to discriminate and is costly. It is seen as
particular protein confidential and may be used for abuse by government
• DNA can replicate to ensure that the genetic which are some arising ethical issues )
code is accurately transferred from one • Play role in regulation and control of the expression of
generation to the next genes in the coding DNA ( where the genes switch on
and off )
• Protects the gene from mutations and controls the
process of copying gene during transcription ( protein
synthesis )
, DNA Replication
• Replication —> the duplication of the DNA molecule to form 2 identical copies and takes place during
Interphase of the cell cycle
• Proteins ( Histones ), together with DNA form part of a chromosome and also duplicate during replication
( identical units are called chromatids )
• Chromatids are held together by a centromere
Process of Replication:
1. Double helix unwinds into 2 strands
2. Weak hydrogen bonds break and the strands unzip
3. Free-floating nucleotides in nucleoplasm build complementary strand onto each of the original two strands
4. DNA Polymerase join the nucleotides
• Each DNA strand served as a template on which its complement forms and each copy comprised of an ‘old’
and ‘new’ strand and the double-stranded structure is what made the replication possible
• Importance of Replication —> during mitotic cell division, one mother cell divides into 2 identical daughter
cells so it is essential that DNA makes identical copies of itself before cell division in order to ensure each
daughter cell contains the same genetic material as the mother.
Ribonucleic Acid ( RNA )
Location Structure
• Nucleus • Single strand that is a polymer with nucleotides and
• Cytoplasm monomers
• Forms part of Ribosomes
Nucleotides:
Formation: • Sugar Molecule —> Ribose
• Forms a single long strand and the bases • Phosphate Group
occurs in any number and ratio • Nitrogenous Base: Adenine, Guanine, Cytosine and Uracil
Types of RNA
Transfer RNA ( tRNA ) Messenger RNA ( mRNA ) Ribosomal RNA ( rRNA )
• Consists of a single • Single strand with an unlimited number of • Consists of a single strand
strand that folds nucleotides • Forms part of the structure
back on itself and it • Formed in the nucleoplasm, using DNA as a of the ribosomes in the
occurs in the template cytoplasm and plays a role in
cytoplasm • MRNA carries the genetic codes from DNA in the control of protein
• 3 exposed bases, the nucleus to the ribosomes in the synthesis
called the anticodon, cytoplasm and thus acts as a messenger
occur on one of the
loops Differences between DNA and RNA
• tRNA picks up amino
acids in the
cytoplasm and takes
them to the
ribosome where
protein synthesis
occurs and it acts as
a transfer molecule
