genetics of living systems Flashcards
what are mutations
changes to DNA base sequence
what are 3 types of changes to DNA, give description and an example
Substitution: one nucleotide exchanged for another , eg sickle cell anaemia
insertion: an extra nucleotide (or more than 1) is places into DNA sequence, eg Huntington’s disease
deletion: a nucleotide (or more than 1) is removed from DNA sequence, eg cystic fibrosis
why do substitution changes to DNA tend to be less harmful then deletion or insertion
substitution change 1 codon and cause a max of 1 amino acid to be altered, insertion and deletion can change many codons along DNA sequence (frameshift) mutation
give the 3 types of mutation, description and the effect
silent: could be in a non-coding region or produce a new codon that codes for the same amino acid (degenerate code). NO EFFECT
nonsense: a codon is changed to a stop codon. Effect: shorter polypeptide, normally harmful
missense: at least 1 new amino acid is introduced into a proteins primary structure. Effect: harmful usually, but sometimes beneficial or neutral
explain why an insertion mutation of 3 nucleotides does not cause a frameshift (3 marks)
(genetic code is a) triplet code,
3 nucleotides represents a codon/code for 1 amino acid,
other codons in DNA sequence will not be altered
give the ways in which gene expression can be controlled
transcription, post-transcription, translation, post-translation
give the control mechanism and description for how transcription controls gene expression
chromatin structural changes: heterochromatin forms during cell division, DNA is wound tightly around histones. No transcription occurs
Euchromatin forms during interphase. DNA is wound loosely around histones. Transcription can occur
transcription factors: molecules bind to DNA to either promote or prevent transcription
epigenetics: acetylation of histones increases transcription rates
methylation of DNA prevents transcription
Operons: genes switched off when repressor binds to an operator region, prevents RNA polymerase binding and stops transcription of structural genes
genes switched on when repressor is removed
give the control mechanism and description for how post-transcription controls gene expression
mRNA processing: splicing introns (non coding DNA) are removed from mRNA. different polypeptides can be formed by retaining some introns and rearranging exons
mRNA editing: mRNA can be edited by adding, deleting or substituting nucleotides
give the control mechanism and description for how translation controls gene expression
control of mRNA binding site: inhibitory proteins prevent binding of mRNA to ribosomes. initiation factors promote mRNA binding
give the control mechanism and description for how post-translation controls gene expression
polypeptide modification: eg protein folding, and the addition of non-protein groups and disulfide bridges
explain how a gene consisting of 930 base pairs can be transcribed into mature mRNA consisting of only 615 nucleotides (2 marks)
introns are removed from pre-mRNA,
the remaining exons are spliced together to form mature RNA
explain the importance of splicing in organisms (2 marks)
alternative splicing enables many different proteins to be translated from a single gene,
this increases genetic diversity, which allows greater complexity in organisms
what is an organisms development reliant on
homeobox genes: an organisms development by a set of regulatory genes
Apoptosis: programmed cell death and mitosis
what steps are involved in apoptosis
cell shrinks, nucleus condenses, enzymes break down cytoskeleton, cell breaks into fragments held in vesicles and macrophages digest the cell fragments
describe 2 examples of apoptosis in an organisms development (2 marks)
formation of connections between neurones,
destruction of harmful immune cells,
forming shapes of organs and tissues,
removing excess cells (eg from between digits),
suggest why species differ in the number of homeobox genes they possess (2 marks)
species differ in complexity of their anatomy,
number of homeobox genes increases with complexity
Necrosis is a damaging form of cell death caused by infection or trauma. Necrotic cells rupture and release hydrolytic enzymes. Outline and explain the differences between apoptosis and necrosis (4 marks)
during necrosis, cells rupture and release enzymes,
necrosis is an uncontrolled process,
apoptosis is an controlled, regulated process,
rather than cells rupturing, cell fragments are packaged into vesicles
