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