OCR BIOLOGY A LEVEL 2022 NEW EXAM SOLUTION PRACTICE SOLUTION
What is a mutation? - Change in the sequence of bases in DNA
What are the three ways the base sequence can be altered? - Substitution, deletion and insertion
What is the term for a mutation where only one nucleotide is affected? - Point mutation
What are the causes of a silent mutation? - degenerate code
new amino acid is similar
amino acid not involved with proteins function
What is the term for a mutation that the genetic code may mean the protein's primary structure is
unaffected? - Silent mutation
What type of mutation can be caused by the insertion or deletion of nucleotides? - Frameshift
mutation
What is a mutagen? - Chemical, physical or biological agent that causes mutations
What are the two types of mutagens? - Depurination and depyrimidation
What do nonsense mutations do? - Make a stop codon where there shouldn't be one
What do missense mutations do? - Result in the formation of the wrong amino acid
What is chromosome deletion? - A section breaks off and is lost within the cell
What is chromosome duplication? - Sections are duplicated
What is chromosome translocation? - A section of one breaks off and joins another
,What is chromosome inversion? - A section breaks off, is reversed and rejoins
When is heterochromatin present? - Cell division
When is euchromatin present? - Interphase
Why does transcription not happen during cell division? - Heterochromatin is too tightly wound for
RNA polymerase to access the genes
Why does chromatin remodelling occur? - So proteins for cell division are synthesised in time and
so energy-consuming protein synthesis does not happen during cell division
What are epigenetics? - Regulating genes by modifying DNA
What happens if histones become less positive? - DNA coils less tightly which increases
transcription
What happens if histones become more hydrophobic? - DNA coils more tightly which prevents
transcription
What can be added to histones to make them less positive? - Acetyl groups or phosphate groups
What can be added to histones to make them more hydrophobic? - Methyl groups
What is an operon? - A group of genes under the control of the same regulatory mechanism and are
expressed at the same time
Which type of organism has more operons? - Prokaryotic
What are the genes in the lac operon? - LacZ, lacY and lacA
,What do the genes in the lac operon code for? - Enzymes
What is the regulatory genes for the lac operon? - LacI
What does LacI code for? - Repressor protein
How does a repressor protein affect the lac operon? - Prevents their transcription in the absence of
lactose
What does a repressor protein bind? - Operator
How does a repressor protein prevent transcription? - Prevents RNA polymerase binding to DNA
What is the promoter? - The section of DNA where RNA polymerase binds
How does lactose affect the repressor protein in the case of the lac operon? - Changes its shape so it
cannot bind to the operator
Why is glucose still preferred over lactose as a respiratory substrate when they are both present? -
cAMP levels decrease in the presence of glucose which reduces the transcription rate of the lac
operon
What is the role of cAMP with regards to the lac operon? - Increase the rate of transcription
What does housekeeping genes code for? - Enzymes constantly required
What does tissue-specific genes code for? - Hormones only required at certain times
What is the product of transcription? - Pre-mRNA
, What are added to pre-mRNA to stabilise it? - A modified nucleotide and an adenine chain (cap and
tail)
Why is a cap and tail added to pre-mRNA? - stabilise it
prevent breakdown
helps bind to ribosomes
What are introns? - Non-coding DNA
What are extrons? - Coding DNA
What happens when RNA is spliced? - Introns are removed and the extrons joined together to form
mature-mRNA
How does the degradation of mRNA regulate protein synthesis? - The more resistant, the longer it
lasts, the more proteins are made
How do inhibitory proteins regulate protein synthesis? - Bind to mRNA to stop it binding to
ribosomes
What are protein kinases? - Enzymes that catalyse the addition of phosphate groups to proteins
How do protein kinases regulate cell activity? - Change tertiary structure of proteins
What are protein kinases usually activated by? - cAMP
What is post-translational control? - Modifications to proteins
What is morphogenesis? - The regulation of the pattern of anatomical development
What is the purpose of a homeodomain? - Switch other genes on or off
What is a mutation? - Change in the sequence of bases in DNA
What are the three ways the base sequence can be altered? - Substitution, deletion and insertion
What is the term for a mutation where only one nucleotide is affected? - Point mutation
What are the causes of a silent mutation? - degenerate code
new amino acid is similar
amino acid not involved with proteins function
What is the term for a mutation that the genetic code may mean the protein's primary structure is
unaffected? - Silent mutation
What type of mutation can be caused by the insertion or deletion of nucleotides? - Frameshift
mutation
What is a mutagen? - Chemical, physical or biological agent that causes mutations
What are the two types of mutagens? - Depurination and depyrimidation
What do nonsense mutations do? - Make a stop codon where there shouldn't be one
What do missense mutations do? - Result in the formation of the wrong amino acid
What is chromosome deletion? - A section breaks off and is lost within the cell
What is chromosome duplication? - Sections are duplicated
What is chromosome translocation? - A section of one breaks off and joins another
,What is chromosome inversion? - A section breaks off, is reversed and rejoins
When is heterochromatin present? - Cell division
When is euchromatin present? - Interphase
Why does transcription not happen during cell division? - Heterochromatin is too tightly wound for
RNA polymerase to access the genes
Why does chromatin remodelling occur? - So proteins for cell division are synthesised in time and
so energy-consuming protein synthesis does not happen during cell division
What are epigenetics? - Regulating genes by modifying DNA
What happens if histones become less positive? - DNA coils less tightly which increases
transcription
What happens if histones become more hydrophobic? - DNA coils more tightly which prevents
transcription
What can be added to histones to make them less positive? - Acetyl groups or phosphate groups
What can be added to histones to make them more hydrophobic? - Methyl groups
What is an operon? - A group of genes under the control of the same regulatory mechanism and are
expressed at the same time
Which type of organism has more operons? - Prokaryotic
What are the genes in the lac operon? - LacZ, lacY and lacA
,What do the genes in the lac operon code for? - Enzymes
What is the regulatory genes for the lac operon? - LacI
What does LacI code for? - Repressor protein
How does a repressor protein affect the lac operon? - Prevents their transcription in the absence of
lactose
What does a repressor protein bind? - Operator
How does a repressor protein prevent transcription? - Prevents RNA polymerase binding to DNA
What is the promoter? - The section of DNA where RNA polymerase binds
How does lactose affect the repressor protein in the case of the lac operon? - Changes its shape so it
cannot bind to the operator
Why is glucose still preferred over lactose as a respiratory substrate when they are both present? -
cAMP levels decrease in the presence of glucose which reduces the transcription rate of the lac
operon
What is the role of cAMP with regards to the lac operon? - Increase the rate of transcription
What does housekeeping genes code for? - Enzymes constantly required
What does tissue-specific genes code for? - Hormones only required at certain times
What is the product of transcription? - Pre-mRNA
, What are added to pre-mRNA to stabilise it? - A modified nucleotide and an adenine chain (cap and
tail)
Why is a cap and tail added to pre-mRNA? - stabilise it
prevent breakdown
helps bind to ribosomes
What are introns? - Non-coding DNA
What are extrons? - Coding DNA
What happens when RNA is spliced? - Introns are removed and the extrons joined together to form
mature-mRNA
How does the degradation of mRNA regulate protein synthesis? - The more resistant, the longer it
lasts, the more proteins are made
How do inhibitory proteins regulate protein synthesis? - Bind to mRNA to stop it binding to
ribosomes
What are protein kinases? - Enzymes that catalyse the addition of phosphate groups to proteins
How do protein kinases regulate cell activity? - Change tertiary structure of proteins
What are protein kinases usually activated by? - cAMP
What is post-translational control? - Modifications to proteins
What is morphogenesis? - The regulation of the pattern of anatomical development
What is the purpose of a homeodomain? - Switch other genes on or off
