Topic 3 The 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
What is the full name 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=T, C=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
- DNA precipitates forming a fibrous white solid
- Use a glass rode to collect the DNA sample
Why is detergent added to the crushed fruit?
It disrupts the 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 than water?
DNA is insoluble in ethanol, encouraging its precipitation
Explain how a gene codes for a protein
- A sequence of three bases in a gene forms a triplet
- Each triplet codes for an amino acid
- The order of amino acids determines the structure (e.g 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
- Translation
What does transcription involve?
The formation of mRNA from a DNA template
Outline transcription
- DNA double helix unwinds
- RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
- RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
- mRNA formation complete. mRNA detaches and leaves the nucleus
Describe the difference between mRNA and DNA
- mRNA is single stranded whereas DNA is double stranded
- mRNA uses U whereas DNA uses T
Why is mRNA used in translation rather than DNA?
DNA is 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 mRNA to form a protein
Outline translation
- mRNA attaches to a ribosome
- Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by tRNA molecule
How is 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 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 acids sequence, protein structure and function may change
- If a mutation does not change amino acid sequence, there is no effect
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?
Scientists didn’t understand Mendel’s work as their was no knowledge of DNA at that time
