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DNAThe Code of Life
Introduction…
DNA→Deoxyribonucleic
acid• This makes up the
genes located on the chromosomes in the nucleus.
RNA→Ribonucleic acid• This is formed in
the nucleus BUT functions in the cytoplasm.
There are two types of nucleic acids…
Structure of Nucleic Acids
• Both DNA and RNA are large molecules.
• They are made up of a number of smaller units or monomers called nucleotides.
Each nucleotide is made up of:•A nitrogenous base (NB)•A sugar portion (S)•Deoxyribose in DNA•Ribose in RNA
•A phosphate portion (P)
Structure of Nucleotide Each nucleotide is made
up of:• A nitrogenous base
(NB)• A sugar portion (S)
• Deoxyribose in DNA
• Ribose in RNA• A phosphate portion
(P)
P
NBS
DNA
1.Location of DNA
2.Structure of DNA
3.Functions of DNA
DNA: Location of DNA• The DNA within the nucleus is called
NUCLEAR DNA. – Together with proteins, it makes up the
chromosomes which in turn go to make up the chromatin network.
• Small amounts of DNA are also found outside the nucleus (extra-nuclear DNA) such as:–Within chloroplasts (called chloroplastic DNA) –Mitochondria (called mitochondrial DNA or
mtDNA)
DNA: Structure of DNA• Structure was discovered by James
Watson and Francis Crick in 1953.• DNA is double stranded i.e. it
consists of two strands of nucleotides joined together by weak hydrogen bonds.
• The natural shape of DNA is a double helix.
• Each DNA nucleotide contains the sugar – deoxyribose.
DNA: Structure of DNA• There are 2 groups of nitrogenous
bases: purines and pyrimidines.• Purines = adenine and guanine
(PUAG)• Pyrimidines = cytosine and thymine
(PYCTH)• The nitrogen bases are
complementary:– Cytosine ONLY with guanine– Adenine ONLY with thymine
P
NBS
Deoxyribose
Purines:•Adenine•Guanine
Pyrimidines:•Cytosine •Thymine
DNA: Structure of DNA
Basic double helix of DNA
DNA: Structure of DNA
DNA: Structure of DNA
DNA: Functions of DNA• DNA codes for the formation of
different proteins required in the body.
• DNA is responsible for transmitting hereditary characteristics form parents to offspring.
RNA
1.Location of RNA
2.Structure of RNA
3.Functions of RNA
RNA: Location of RNA• There are 3 types of RNA:
1. Ribosomal RNA (rRNA) found in the ribosomes in the cytoplasm of the cell.
2. Messenger RNA (mRNA) which is found in the nucleus and attaches to the ribosome in the cytoplasm.
3. Transfer RNA (tRNA) found in the cytoplasm of the cell.
RNA: Structure of RNA
• Ribonucleic Acid (RNA) is similar to DNA except that:– It is a single stranded
structure.–The sugar in it is RIBOSE.–Thymine is replaced by
URACIL.–The bases are not paired.
RNA: Functions of RNA
• All three types of RNA play important roles in PROTEIN SYNTHESIS.
Similarities between DNA and RNA
Both contain sugar alternating with phosphate.
Both contain the nitrogenous bases ADENINE, GUANINE and CYTOSINE.
Both play a role in protein synthesis.
Similarities between DNA and RNA
DNA• Found in the
nucleus, chloroplast and mitochondria.
• Double stranded molecule.
• Contains the sugar deoxyribose.
• Contains the nitrogenous base thymine.
RNA• Found in the nucleus
and cytoplasm.
• Single stranded molecule.
• Contains the sugar ribose.
• Contains the nitrogenous base uracil.
Similarities between DNA and RNA
DNA• Found in the
nucleus, chloroplast and mitochondria.
• Double stranded molecule.
• Contains the sugar deoxyribose.
• Contains the nitrogenous base thymine.
RNA• Found in the nucleus
and cytoplasm.
• Single stranded molecule.
• Contains the sugar ribose.
• Contains the nitrogenous base uracil.
Similarities between DNA
and RNA
Similarities between DNA
and RNA
DNA Replication
DNA Replication• What is DNA replication?– The process by which DNA makes an identical copy of
itself.
• When does it occur?– DNA replication occurs just before cell division
(mitosis and meiosis). It occurs during interphase.
• Why does it occur?– DNA replication is a process by which identical copies
of DNA are made so that it could be shared amongst the daughter cells during cell division so that each daughter cell has the same number of chromosomes as the original.
– It allows the daughter cells after mitosis to be identical to each other and to the cell from which they were formed.
DNA Replication
HOW DOES IT OCCUR?Double helix DNA unwinds.Weak hydrogen bonds between nitrogenous bases
break.Two DNA strands unzip/separate.Each original DNA strand serves as a template to
form a new strand by attaching to free nucleotides from the nucleoplasm.
This forms complementary strands (A to T and C to G).
Each DNA molecule now consists of 1 original strand and 1 new strand.
The result is two genetically identical DNA molecules.
The entire process is controlled by enzymes.
http://www.hhmi.org/biointeractive/dna-replication-advanced-detail
DNA Profile
• What is a DNA profile?– DNA profiles are patterns of black bars
left on X-Ray film when an extract of DNA is put through a special biotechnical process. • This is called PCR (Polymerase Chain Reaction)
– DNA profiling is a method of identifying an individual by comparing his/her DNA profile with another known DNA profile.
DNA Profile
• What are the uses of DNA Profiles?–DNA profiles are used for:• The diagnosis of inherited disorders
such as cystic fibrosis, haemophilia and sickle cells anaemia.• Identificaiton of criminals in forensic
science.• Identification of relatives such as:– Establishing whether a particular person is
the father of a child or not.– Tracing siblings (brothers and sisters) who
have been separated at birth.– Identifying people who have died and
where their bodies cannot be recognised.
DNA Profile
Debates around
DNA Profiling
The small piece of DNA may NOT be unique to an
individual
Uniform testing
standards & quality
controls may be lacking in
private laboratories
Human error could occur
during interpretation of the results
DNA profiling is expensive
Profiling may reveal
personal information
like HIV which could lead to
prejudice
THE END