Genome Flashcards
What is DNA?
A double-stranded polymer of
nucleotides, wound to form a double
helix
What are the monomers of DNA?
Nucleotides
What are DNA nucleotides made up of
● Common sugar
● Phosphate group
● One of four bases:A, T, C or G
State the full names of the four bases found in
nucleotides
● Adenine
● Thymine
● Cytosine
● Guanine
Describe how nucleotides interact to form a molecule of DNA
● Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
● Base connected to each sugar
● Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds
Define genome
The entire genetic material of an
organism
What is a chromosome?
A long, coiled molecule of DNA that carries genetic information in the form of genes
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
Describe the method used to extract DNA from fruit
- Place a piece of fruit in a beaker and crush it
- Add detergent and salt, mix
- Filter the mixture and collect the liquid in a test tube
- Pour chilled ethanol into the test tube
- DNA precipitates forming white solid strands
- Use a glass rod to collect the DNA sample
Why is detergent added to the crushed fruit?
It disrupts the nuclear and cell membranes, releasing DNA into solution
Why is salt added to the crushed fruit?
Salt encourages the precipitation of DNA
Why is chilled ethanol added rather water?
DNA is insoluble in ethanol, encouraging its precipitation
Explain how a gene codes for a protein
● Asequence of three bases in a gene forms a triplet
● Each triplet codes for an amino acid
● The order of amino acids determines the structure
(i.e. how it will fold) and function of protein formed
Why is the ‘folding’ of amino acids important in
proteins such as enzymes?
The folding of amino acids determines the
shape of the active site which must be
highly specific to the shape of its substrate.
What is protein synthesis?
The formation of a protein from a gene
What are the two stages of protein synthesis?
- Transcription
2. Translation
What does transcription involve?
The formation of mRNA from a DNA
template
Outline transcription
- DNAdouble helix unwinds
- RNApolymerase binds to a specific base sequence of non-coding
DNAin front of a gene and moves along the DNA strand - RNApolymerase joins free RNAnucleotides to complementary bases
on the coding DNA strand - mRNAformation complete. mRNAdetaches and leaves the nucleus.
Describe the difference between mRNA and DNA
● mRNAis single stranded whereas
DNAis double stranded
● mRNAuses U whereas DNAuses T
Why is mRNA used in translation rather than DNA?
DNAis too large to leave the nucleus so
cannot reach the ribosome.
What does translation involve?
A ribosome joins amino acids in a
specific order dictated by mRNAto form
a protein.
Outline translation
- mRNAattaches to a ribosome
- Ribosome reads the mRNA bases in triplets. Each triplet codes
for one amino acid which is brought to the ribosome by a tRNA
molecule - A polypeptide chain is formed from the sequence of amino
acids which join together
How is a tRNA molecule adapted to its function?
Each tRNA molecule has an anticodon
which is specific to the codon of the
amino acid that it carries.
What is a mutation?
A random change in the base sequence
of DNA which results in genetic variants
Describe the effect of a gene mutation in coding
DNA
● If a mutation changes the amino acid sequence,
protein structure and function may change
● If a mutation does not change amino acid sequence,
there is no effect on protein structure or function
What is non-coding DNA?
DNA which does not code for a protein
but instead controls gene expression
Describe the effect of a gene mutation in
non-coding DNA
● A mutation may affect the ability of RNA
polymerase to bind to non-coding DNA
● This may affect protein production and the
resulting phenotype of the organism
Outline how the work of Mendel helped scientists to
develop their understanding of genetics
● Mendel studied the inheritance of different phenotypes of pea plants
● He established a correlation between parent and offspring phenotypes
● He noted that inheritance was determined by ‘units’ passed on to
descendants
● Using gene crosses, he devised the terms ‘dominant’ and ‘recessive’
Why was Mendel’s work initially
overlooked?
Scientist’s didn’t understand Mendel’s
work as there was no knowledge of
genes or DNA at the time.
