The Watson-Crick Model of DNA

Biology

In ____, two scientists, _______ _______ and _______ ________ in England used _-____ data obtained by ___________ _________ to discover the __________ of the ___________ that encodes our ___________ _____________. This is the _____ molecule.

1953, James Watson, Francis Crick, Rosalind Franklin, structure, molecule, genetic information. DNA.

What does DNA stand for?

Deoxyribose nucleic acid.

What is the shape of the DNA molecule?

A double helix.

What do the two strands of the double helix resemble?

A spiral staircase.

What are the two strands of the double helix called?

Sugar Phosphate Backbones

What are the two strands of the double helix composed of?

Molecules called nucleotides.

What are nucleotides composed of?

A phosphate group (forms bond between sugar molecules), a deoxyribose sugar molecule (5 carbon sugar), and a nitrogen base.

What are the spiral steps composed of?

The nitrogen bases.

What are the sides of the 'spiral staircase' composed of?

The phosphate groups and deoxyribose sugar molecules.

What are the four types of nitrogen bases?

Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

What are Adenine and Guanine called?

Purines (Double ring)

What are Thymine and Cytosine called?

Pyrimidines (Single ring)

Is the structure of DNA parallel or anti-parallel?

Anti-parallel.

Prior to normal ______ _____________, each DNA molecule must make a copy of itself. This process is called ____________.

Cell division. Replication.

Each new cell will have an _________ copy of each DNA molecule.

Exact.

What is the first step of replication?

The nitrogen bases that form the 'spiral steps' start to split apart at one end of the DNA ladder.
The double helix of the parental DNA separates as weak hydrogen bonds between the nucleotides on opposite strands break in response to the action of replication enzymes.

What is the second step of replication?

New nucleotides are transported into place and linked together to produce a complementary strand according to the rule for base pairing (Adenine with Thymine, and Guanine with Cytosine - DNA polymerase).
Hydrogen bonds form between new complementary nucleotides and each strand to form new base pairs.

What is the third step of replication?

Two new double helices form when this process is completed.
Enzymes catalyse the formation of sugar-phosphate bonds between sequential nucleotides on each resulting daughter strand.

The __________ codes (3 __________ base code) in the DNA molecules are associated with a particular _________ ________.

Triple, nitrogen, amino acid.

What is an amino acid?

A simple organic compound containing both a carboxyl (-COOH) and an amino (-NH2) group.

The process of a DNA replication may go wrong, which can result in a change in the __________ of __________ bases in the DNA molecule. This change in the code is called a DNA ____________.

Sequence, nitrogen. Mutation.

What is deletion?

A base is lost. (e.g. AAA becomes AA)I

What is insertion?

An extra base is inserted.

What can deletion and insertion cause?

A 'frameshift', which changes the amino acid squence.

What is substituion?

One base is substituted for another (e.g. AAA becomes AAG).

What is it called when a substitution changes the amino acid? (E.g. AAA becomes AGA)

A missense mutation.

What is it called when a substitution does not change the amino acid? (E.g. AAA becomes AAG)

Silent mutation.

What is it called when a substitution changes the amino acid to a "STOP"?

Nonsense mutation.

What is an example of DNA mutation?

Sickle Cell anaemia.

DNA molecules are packaged into _____________.

Chromosomes.

Every _________ species has a characteristic number of ___________ in the _________.

Eukaryotic, chromosomes, nucleus.

What is a eukaryotic?

Consisting of complex cells with a nucleus and define organelles.

How many chromosomes do human somatic cells (body cells) have?

46.

How many chromosomes do human gametes (sperm or eggs) have?

23.

Each eukaryotic chromosome consists of a ______, ________ DNA molecule.

Long, linear.

A molecule of DNA is:

A single-stranded chromosome.

Chromosomes may be _________ or _________ stranded.

Single, double.

The two strands of a double-stranded chromosome are __________. They are formed during DNA ____________ so that two ___________ __________ - one for each of the two cells formed during cell ___________ (___________) - can be produced.

Identical. Replication, identical copies, division, mitosis.

What is each strand of a double-stranded chromosome called?

A chromatid.

What is a double-stranded chromosome made up of?

Two sister chromatids joined at the centromere.

Single-stranded chromosomes -> double-stranded chromosomes -> separation of sister chromatids = ?

DNA replication.

What are genes?

Sections of a DNA molecule.

The base sequence of each gene contains information for _____ ______________.

One characteristic.

What does the cell contain?

The nucleus.

What does the nucleus contain?

The chromosomes.

What do the chromosomes contain?

The DNA.

What do the DNA contain?

Genes.

What are gene codes?

They contain information about inheritance.

Genes are _________ of the DNA molecule containing many _________ __________.

Segments, triplet codes.

What is each gene responsible for?

The production of a certain protein.

What are gene segments of the DNA strands separated from one another by?

Non-coding segments.

What are non-coding segments?

Introns: They interrupt genetic code.
Exons: Coding regions of DNA.

Do genes function at all times?

No, they can be turned on or off.

What are a gene's two alternative forms called?

Alleles.