LIFE SCIENCES PI
DNA, GENETICS AND GENETIC ENGINEERING
NUCLEIC ACIDS
Deoxyribonucleic Acid
Location
– Mainly in nucleus as chromosomal DNA forming part of the chromatin network
– Otherwise in mitochondria and chloroplasts as extranuclear DNA
Chromosomes and Genes
– Chromosome: long, thread-like structure composed of DNA wrapped around histone
proteins
– Only visible in dividing cell
– Gene: short segment of a DNA molecule that codes for a particular protein
– Each gene carries the code for the synthesis of a protein
– Proteins determine characteristics of organisms (structure & function)
Discovery of the Structure of DNA
– Double-helix structure formulated by James Watson and Francis Crick in 1953 after seeing
x-ray photos taken by Rosalind Franklin shown to them by Maurice Wilkins without
Franklin’s permission and building three dimensional structures of DNA.
– Watson and Crick and Wilkins were awarded the Nobel price for Physiology/Medicine for
their discovery of DNA’s structure and description of the double-helix structure in an
article. Franklin got no recognition as she had passed away before the prize was awarded.
Structure of DNA
– A giant molecule (2m long) consisting of two strands twisted to form a double helix
– A polymer made of many monomers (similar building blocks), called nucleotides
Nucleotides
– Consist of three parts
– Sugar molecule - Deoxyribose (D)
– Phosphate group (P)
– Nitrogenous base
– Adenine (A)
– Thymine (T)
– Cytosine (C)
– Guanine (G)
, – A and G are large molecules known as purine bases
– C and T are smaller molecules known as pyrimidine bases
– D combines with the P. One nitrogenous base combines with D (therefore there are 4
different nucleotides in DNA)
Formation of DNA
– The D from one nucleotide bonds with the P of another nucleotide, forming the ‘side of the
ladder’ made of alternating D and Ps.
– The rungs of the ladder are made of base pairs - purine bases bonded to a pyrimidine
bases by weak hydrogen bonds that are easily broken by enzyme action
– A & T always bond to each other with 2 H-bonds
– G & C always bond to each other with 3 H-bonds
– There is always an equal number of As and Ts, and Gs and Cs in a DNA molecule. I.e. A =
T, G = C
– The sequence of nitrogenous bases provides the code that gives the instructions for the
synthesis of proteins. The sequence is known as the ‘genetic code’ or ‘code of life’
– The sequence of one DNA strand (the template) determines the sequence of its
complementary strand
Role of DNA
Genes
– Each gene has a specific sequence of nitrogenous bases which determine the sequence of
amino acids which will bond together to form a protein
– DNA replication ensures that genetic code is accurately transferred throughout
generations
Non-coding DNA
– About 2% of DNA codes for proteins. The other 98% (non-coding DNA) varies greatly
between humans and is used for DNA profiling/fingerprinting
– Plays a role in the regulation and control of the expression of genes in coding DNA
(determines when and where genes are turned on and off)
DNA Replication
– Duplication of the DNA molecule and the histones that form a part of the chromosome
– Takes place during interphase of the cell cycle. Two identical chromatids are formed which
are joined by a centromere to form a chromosome
Process
– Double helix structure unwinds and untwists
– Strands unzip when weak hydrogen bonds break
– Free-floating nucleotides in nucleoplasm build a complementary DNA strand onto each
original DNA strand. The enzyme DNA polymerase controls the joining of nucleotides
Importance
– During mitosis, one mother cell divides into two identical daughter cells. DNA must make
identical copies of itself before cell divisor to ensure the daughter cells have the same
genetic information as the mother cell.
,Mitochondrial DNA (mtDNA)
– Unrelated to chromosomal DNA. Shorter, circular in shape in comparison to chromosomal
DNA
– Genes of mtDNA code for enzymes that control cellular respiration
mtDNA and Relatedness
– Sperm contains 1% of mitochondria of ova. Most of these mitochondria occur in sperm tail
and are discarded when the sperm fuses with an ovum. Therefore, the mitochondria that
remain in the zygote are those belonging to the ovum.
– Therefore, mtDNA is only inherited via the maternal line in the pedigree, and can be used
to trace maternal lines throughout generations as it remains relatively unchanged over
long periods of time. mtDNA is used to determine how closely related different organisms
are.
Ribonucleic Acid
Location
– Occurs in nucleus and cytoplasm
– Forms part of ribosomes
Structure
– Single-straded polymer with nucleotides as momomers
Nucleotides
– Consist of three parts
– Sugar molecule - Ribose (R)
– Phosphate group (P)
– Nitrogenous base
– Adenine (A)
– Uracil (U)
– Cytosine (C)
– Guanine (G)
Formation of RNA
– The R of one nucleotide joins to the P of another and so on to form a single strand
– Nitrogenous bases occur in any number, ratio, or sequence
Types of RNA
Messenger RNA (mRNA)
– Single strand with unlimited number of nucleotides
– Formed in the nucleoplasm using DNA as a template
– Carries the genetic code from DNA in the nucleus to ribosomes in the cytoplasm, thus
acting like a messenger
Transfer RNA (tRNA)
– Single strand which folds back on itself and/or forms loops
– Occurs in the cytoplasm
, – Three exposed bases, the anticodon, occur on one of the loops of RNA
– Picks up amino acids in the cytoplasm and takes them to ribosomes where protein
synthesis occurs, thus acting as a transfer molecule
PROTEIN SYNTHESIS
– Three consecutive nitrogenous bases on a DNA strand code for a particular amino acid,
and are known as a base triplet
– The sequence of base triplets in DNA determines the sequence in which amino acids will
link and therefore the protein that will be formed
Transcription of DNA
– RNA polymerase breaks the hydrogen bonds of the DNA and the two strands unzip in the
region where a gene which codes for a protein is located
– RNA polymerase binds free-floating RNA nucleotides to the template DNA strand, forming
a complementary RNA strand. A single strand of RNA is formed
– Each group of three nitrogenous bases in RNA, known as a codon, codes for a specific
amino acid. The sequence of nitrogenous bases on RNA is the complement of the
sequence of the base triplets on the DNA.
– As the mRNA forms, it moves away from the DNA and the two DNA strands join again and
reform a double helix. The mRNA leaves the nucleus through a nucleopore and takes its
code to ribosomes in the cytoplasm
Translation of RNA to Proteins
– Singular mRNA strand attaches to ribosome.
– tRNA picks up amino acids in the cytoplasm and brings them to the ribosome. The
anticodon on a tRNA strand determines which amino acid it will carry
– Anticodons on tRNA bond to complementary codons on mRNA. As sequential tRNA
strands bond to an mRNA strand, their amino acids bond to each other with peptide bonds
– As soon as a tRNA’s amino acid has bonded successfully to the next amino acid, the mRNA
breaks its bond with the amino acid and the mRNA and moves away from the ribosome,
ready to pick up another amino acid.
– When 50 or more amino acids are joined, a protein is formed when a stop codon occurs
and the polypeptide chain bends itself into the proper required shape
MUTATIONS
– Any change in the genetic composition of an organism
– May occur spontaneously by chance, or as a result of mutagens
– Mutagens: physical or chemical agents causing mutations)
– X-rays
– UV light
– Toxic chemicals
– Viral infections
– Extreme heat
DNA, GENETICS AND GENETIC ENGINEERING
NUCLEIC ACIDS
Deoxyribonucleic Acid
Location
– Mainly in nucleus as chromosomal DNA forming part of the chromatin network
– Otherwise in mitochondria and chloroplasts as extranuclear DNA
Chromosomes and Genes
– Chromosome: long, thread-like structure composed of DNA wrapped around histone
proteins
– Only visible in dividing cell
– Gene: short segment of a DNA molecule that codes for a particular protein
– Each gene carries the code for the synthesis of a protein
– Proteins determine characteristics of organisms (structure & function)
Discovery of the Structure of DNA
– Double-helix structure formulated by James Watson and Francis Crick in 1953 after seeing
x-ray photos taken by Rosalind Franklin shown to them by Maurice Wilkins without
Franklin’s permission and building three dimensional structures of DNA.
– Watson and Crick and Wilkins were awarded the Nobel price for Physiology/Medicine for
their discovery of DNA’s structure and description of the double-helix structure in an
article. Franklin got no recognition as she had passed away before the prize was awarded.
Structure of DNA
– A giant molecule (2m long) consisting of two strands twisted to form a double helix
– A polymer made of many monomers (similar building blocks), called nucleotides
Nucleotides
– Consist of three parts
– Sugar molecule - Deoxyribose (D)
– Phosphate group (P)
– Nitrogenous base
– Adenine (A)
– Thymine (T)
– Cytosine (C)
– Guanine (G)
, – A and G are large molecules known as purine bases
– C and T are smaller molecules known as pyrimidine bases
– D combines with the P. One nitrogenous base combines with D (therefore there are 4
different nucleotides in DNA)
Formation of DNA
– The D from one nucleotide bonds with the P of another nucleotide, forming the ‘side of the
ladder’ made of alternating D and Ps.
– The rungs of the ladder are made of base pairs - purine bases bonded to a pyrimidine
bases by weak hydrogen bonds that are easily broken by enzyme action
– A & T always bond to each other with 2 H-bonds
– G & C always bond to each other with 3 H-bonds
– There is always an equal number of As and Ts, and Gs and Cs in a DNA molecule. I.e. A =
T, G = C
– The sequence of nitrogenous bases provides the code that gives the instructions for the
synthesis of proteins. The sequence is known as the ‘genetic code’ or ‘code of life’
– The sequence of one DNA strand (the template) determines the sequence of its
complementary strand
Role of DNA
Genes
– Each gene has a specific sequence of nitrogenous bases which determine the sequence of
amino acids which will bond together to form a protein
– DNA replication ensures that genetic code is accurately transferred throughout
generations
Non-coding DNA
– About 2% of DNA codes for proteins. The other 98% (non-coding DNA) varies greatly
between humans and is used for DNA profiling/fingerprinting
– Plays a role in the regulation and control of the expression of genes in coding DNA
(determines when and where genes are turned on and off)
DNA Replication
– Duplication of the DNA molecule and the histones that form a part of the chromosome
– Takes place during interphase of the cell cycle. Two identical chromatids are formed which
are joined by a centromere to form a chromosome
Process
– Double helix structure unwinds and untwists
– Strands unzip when weak hydrogen bonds break
– Free-floating nucleotides in nucleoplasm build a complementary DNA strand onto each
original DNA strand. The enzyme DNA polymerase controls the joining of nucleotides
Importance
– During mitosis, one mother cell divides into two identical daughter cells. DNA must make
identical copies of itself before cell divisor to ensure the daughter cells have the same
genetic information as the mother cell.
,Mitochondrial DNA (mtDNA)
– Unrelated to chromosomal DNA. Shorter, circular in shape in comparison to chromosomal
DNA
– Genes of mtDNA code for enzymes that control cellular respiration
mtDNA and Relatedness
– Sperm contains 1% of mitochondria of ova. Most of these mitochondria occur in sperm tail
and are discarded when the sperm fuses with an ovum. Therefore, the mitochondria that
remain in the zygote are those belonging to the ovum.
– Therefore, mtDNA is only inherited via the maternal line in the pedigree, and can be used
to trace maternal lines throughout generations as it remains relatively unchanged over
long periods of time. mtDNA is used to determine how closely related different organisms
are.
Ribonucleic Acid
Location
– Occurs in nucleus and cytoplasm
– Forms part of ribosomes
Structure
– Single-straded polymer with nucleotides as momomers
Nucleotides
– Consist of three parts
– Sugar molecule - Ribose (R)
– Phosphate group (P)
– Nitrogenous base
– Adenine (A)
– Uracil (U)
– Cytosine (C)
– Guanine (G)
Formation of RNA
– The R of one nucleotide joins to the P of another and so on to form a single strand
– Nitrogenous bases occur in any number, ratio, or sequence
Types of RNA
Messenger RNA (mRNA)
– Single strand with unlimited number of nucleotides
– Formed in the nucleoplasm using DNA as a template
– Carries the genetic code from DNA in the nucleus to ribosomes in the cytoplasm, thus
acting like a messenger
Transfer RNA (tRNA)
– Single strand which folds back on itself and/or forms loops
– Occurs in the cytoplasm
, – Three exposed bases, the anticodon, occur on one of the loops of RNA
– Picks up amino acids in the cytoplasm and takes them to ribosomes where protein
synthesis occurs, thus acting as a transfer molecule
PROTEIN SYNTHESIS
– Three consecutive nitrogenous bases on a DNA strand code for a particular amino acid,
and are known as a base triplet
– The sequence of base triplets in DNA determines the sequence in which amino acids will
link and therefore the protein that will be formed
Transcription of DNA
– RNA polymerase breaks the hydrogen bonds of the DNA and the two strands unzip in the
region where a gene which codes for a protein is located
– RNA polymerase binds free-floating RNA nucleotides to the template DNA strand, forming
a complementary RNA strand. A single strand of RNA is formed
– Each group of three nitrogenous bases in RNA, known as a codon, codes for a specific
amino acid. The sequence of nitrogenous bases on RNA is the complement of the
sequence of the base triplets on the DNA.
– As the mRNA forms, it moves away from the DNA and the two DNA strands join again and
reform a double helix. The mRNA leaves the nucleus through a nucleopore and takes its
code to ribosomes in the cytoplasm
Translation of RNA to Proteins
– Singular mRNA strand attaches to ribosome.
– tRNA picks up amino acids in the cytoplasm and brings them to the ribosome. The
anticodon on a tRNA strand determines which amino acid it will carry
– Anticodons on tRNA bond to complementary codons on mRNA. As sequential tRNA
strands bond to an mRNA strand, their amino acids bond to each other with peptide bonds
– As soon as a tRNA’s amino acid has bonded successfully to the next amino acid, the mRNA
breaks its bond with the amino acid and the mRNA and moves away from the ribosome,
ready to pick up another amino acid.
– When 50 or more amino acids are joined, a protein is formed when a stop codon occurs
and the polypeptide chain bends itself into the proper required shape
MUTATIONS
– Any change in the genetic composition of an organism
– May occur spontaneously by chance, or as a result of mutagens
– Mutagens: physical or chemical agents causing mutations)
– X-rays
– UV light
– Toxic chemicals
– Viral infections
– Extreme heat
