Topic 4 - Genetic information, variation and relationships between organisms

Question 1

What is a gene?

Answer 1

A section of DNA which codes for a protein

Question 2

What is an allele?

Answer 2

They can differ in their nucleotide sequence and can result in variations in inherited traits among individuals.

Question 3

What is the genetic code?

Answer 3

Set of rules defining how the 4 letter code of DNA is translated into the 20 letter code of amino acids.

Question 4

What are the features of the genetic code?

Answer 4

• Code is non-overlapping (each base can only be read once)
• Code is universal (The same for all organisms, Indirect evidence for evolution)
• Code is degenerate (Most amino acids are coded for by more than one triplet)

Question 5

DNA in prokaryotic vs eukaryotic cells

Answer 5

• DNA molecules are shorter, form a circle and are not associated with protein molecules, therefore they do not have chromosomes
• In eukaryotic cells, they are longer and linear and are associated with histones to form chromosomes.

Question 6

How do the mitochondria and chromosomes of eukaryotic cells contain DNA?

Answer 6

• Contain DNA similar to prokaryotic cells as it is short, circular and not associated with proteins

Question 7

Can you describe how a DNA molecule and its associated proteins form a chromosome?

Answer 7

• Two threads join together at a single point.
• Each thread is known as a chromatid because DNA has already replicated to give 2 identical DNA molecules. The DNA in chromosomes is held by histones

Question 8

What is meant by genome and proteome?

Answer 8

• Genome = The complete set of genes in a cell, including those in mitochondria and/or chloroplasts
• Proteome = The full range of proteins produced by the genome.

Question 9

What is the structure of RNA?

Answer 9

• Pentose sugar ribose
• AGCU
• A phosphate group

Question 10

Where would you find rRNA?

Answer 10

• In ribosomes in the cytoplasm of a cell

Question 11

Describe the structure and function of mRNA

Answer 11

• Thousands of mononucleotides, is a long strand that is arranged in a single helix.
• Sequence is determined by sequence of bases on a section DNA during transcription.
• Leaves nucleus via nuclear pores and enters cytoplasm and associates with ribosomes, acting as a template for protein synthesis.

Question 12

Describe the structure and function of tRNA

Answer 12

• Relatively small molecule that is made up of roughly 80 nucleotides
• Single stranded chain folded into a clover-leaf shape with one end of the chain extending beyond the other
• This leaves an area where an amino acid can easily attach to.

Question 13

What is a gene mutation?

Answer 13

Any change to one or more nucleotide bases, or a change in the sequence of the bases in a strand of DNA

Question 14

How and when do gene mutations arise?

Answer 14

Formation of gametes or inheritance.

Question 15

Can you list the principles of natural selection?

Answer 15

• Variation (caused by mutation)
• Selection (change in environment)
• Inheritance (passed onto offspring)
• Change in allele frequency

Question 16

Explain how reproductive success affects allele frequency within a gene pool

Answer 16

Alleles that contribute to traits enhancing reproductive success, such as fertility, survival, or attractiveness, tend to become more common over generations, as individuals with these alleles are more likely to pass them on to the next generation.

Question 17

Can you describe directional selection, exemplified by antibiotic resistant in bacteria?

Answer 17

Directional selection is when a population will have to shift to either extreme due to a mutation that lowers survival rate
Shift to right means more antibiotic resistant for bacteria, so higher survival rate