5 minute read
Achievement criteria and explanatory notes
Achievement Standard
2.7 Gene expression
Key terms
Nucleic acids base pairing rule DNA double helix gene expression hydrogen bond nucleic acid nucleotide RNA
Genetic code and protein synthesis codon degeneracy globular protein fibrous protein mRNA polypeptide protein redundancy rRNA transcription translation triplet code tRNA
Metabolic pathways deletion (mutation) environment
enzyme genotype insertion (mutation) metabolic pathway mutagen mutation phenotype substitution (mutation) The genetic code is the set of rules by which information encoded in genes is translated into proteins by cells. Catalytic proteins, called enzymes, regulate metabolic pathways and are involved in determining phenotype. Mutation and environmental effects can affect phenotype.
Achievement criteria and explanatory notes
Achievement criteria for achieved, merit, and excellence
c A Demonstrate understanding of gene expression: Define and use annotated diagrams or models to explain gene expression. Give characteristics of, or provide an account of, gene expression. c M Demonstrate in-depth understanding of gene expression: Provide a reason as to how or why biological processes affect gene expression. c E Demonstrate comprehensive understanding of gene expression: Link biological ideas and processes about gene expression. The discussion may involve justifying, relating, evaluating, comparing and contrasting, or analysing.
Explanatory notes: Gene expression
Gene expression involves a selection from ...
c 1a Nucleic acid structure. c b The nature of the genetic code. c 2 Proteins and their significance. c 3 Protein synthesis. c 4 The determination of phenotype via metabolic pathways. c 5 Effect of environment on genotype through mutations. c 6 Effect of environment on expression of phenotype. Activity number
99 - 103 106 107
110 -113
104 - 109
117 118
119 - 125
126 127
Nucleic acid structure and the genetic code
Activity number
Select biological ideas and processes from...
c i Molecular components of nucleic acids and their role in carrying the genetic code. 99 - 104 c ii Nature of the genetic code including triplets, codons, and anticodons. 106 - 108 c iii Redundancy due to code degeneracy. 106
Significance of proteins
Activity number
Select biological ideas and processes from...
c i Proteins as the products of gene expression: DNA mRNA polypeptide. 104 c ii Identification of one gene one polypeptide relationship. 104 c iii Significance of proteins with reference to their structural and catalytic roles. 110 - 113
Protein synthesis
Select biological ideas and processes from...
c i The role of the DNA sequence in determining the structure of a protein and how that protein is produced by transcription and translation. Activity number
104 - 110
Select biological ideas and processes from...
c i Biochemical reactions are catalysed by specific enzymes and every enzyme is encoded by a specific gene(s).
117 - 118
c ii Biochemical reactions do not occur in isolation but form part of a chain reaction in which the product of one reaction becomes the substrate of the next.
117 - 118
c iii Phenotype is determined by the presence, absence, or amount of metabolic products. 117 - 118
Select biological ideas and processes from...
c i Mutagens (recognise specific mutagens but not their effect at the molecular level). 120 c ii The potential effect on genotype and phenotype of mutations at the gene level. 121 - 124 c iii Ideas and processes relating to the effect of environment on phenotype involve how environmental factors may change phenotype without changing genotype.
119 125 126
What you need to know for this Achievement Standard
Nucleic acids and the genetic code
Activities 99 - 104, 106 - 107, 114 - 116
By the end of this section you should be able to: c Recognise DNA and RNA as nucleic acids made from nucleotide monomers. Describe their biological roles. c Describe the structure of a nucleotide. State the role of the five-carbon sugar (deoxyribose or ribose), phosphate, and nitrogenous bases in its structure and function. c Describe the double-helix model of DNA. Describe complementary base pairing in DNA and demonstrate an understanding of the base-pairing rule. c Contrast the structure and roles of RNA and DNA. c Describe and explain the main features of the genetic code, including: • the 4-letter alphabet and 3-letter triplet code (codon) of base sequences. • the non-overlapping, linear nature of the code which is read in one direction from start to finish. • The degeneracy of the code and how this leads to redundancy.
Proteins and protein synthesis
Activities 104 - 116
By the end of this section you should be able to: c Outline flow of information from DNA mRNA polypeptide or protein. Describe the one gene-one polypeptide relationship. c Describe the basic structure of amino acids and proteins. Describe the structural roles of fibrous proteins and the catalytic roles of globular proteins. c Identify transcription and translation as the two stages of gene expression. c Explain transcription in eukaryotes, including the role of enzymes in the process. c Explain translation in eukaryotes, including the role of mRNA, tRNA, ribosomes, and enzymes.
Metabolic pathways, mutation, and phenotype
Activities 117 - 128
By the end of this section you should be able to: c Explain how, in a metabolic pathway, the end product of one reaction can be the substrate for the next in a series of linked reactions. Each reaction is catalysed by an enzyme. c Use examples to explain how phenotype is determined via metabolic pathways. c Use examples to explain how mutagens can change genotype through mutation. c Describe types of gene and chromosome mutations and outline their general effect on phenotype. c Use examples to explain how the environment can affect the phenotype without any alteration to genotype. You can include reference to the physical (external) environment and the effect of chemical signatures and markers that control the expression of genes (epigenetic factors).
