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What is a mutation?
An alteration to the DNA base sequence. Often arise spontaneous during DNA replication.
Why might a mutation not lead to change in the amino acid sequence? (2)
Genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet
Mutation may occur in intron
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another.
This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost.
This is more likely to be harmful and significant, as it leads to a frame shift which means the entire amino acid sequence will be different.
What is a mutagenic agent? Give examples
Factors that increase the rate of gene mutation.
X-rays
UV light
gamma rays
certain chemicals in alcohol and tobacco
What is a polyploidy chromosome mutation?
Where an individual has three or more sets of chromosomes instead of two
What is chromosome non-disjunction?
When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.
What is meiosis?
A form of cell division that produces four genetically different haploid cells (half the number of chromosomes in parent cell) known as gametes.
Compare meiosis and mitosis
Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells.
Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells.
What happens during meiosis I?
Homologous chromosomes pair to form bivalents.
Crossing over (exchange of sections of genetic material) occurs at chiasmata.
Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy. What happens
What happens during meiosis II?
Independent segregation of sister chromatids.
Each cell divides again, producing 4 haploid cells.
Draw diagrams to show cell contents after each stage of meiosis.
In which two ways does meiosis produce genetic variation?
Crossing over during meiosis I (resulting in new combinations of alleles)
Independent segregation/assortment of homologous chromosomes and sister chromatids (resulting in new combinations of alleles)
Define population
All the organisms of a particular species that live in the same place.
What is an allele?
Different forms of a particular gene, found at the same locus (position) on a chromosome.
A single gene could have many alleles.
Define genetic diversity.
The total number of different alleles in a population.
What advantage does a high genetic diversity provide?
Ability to adapt to a change in environment
Allows natural selection to occur
Explain how natural selection results in development of new characteristics.
Random mutations result in new alleles.
Some alleles provide an advantage, making an individual more likely to survive and reproduce.
Their offspring receives the new allele, and frequency continues to increase over many generations.
What is biodiversity?
The variety of living organisms. It can be measured in terms of species diversity (no. of species in a community) , ecosystem diversity (range of different habitats) and genetic diversity. Def
Define community
All the different species that live in one area and interact with each other.
How do you calculate index of diversity (d)?
Name four ways we can compare genetic diversity between organisms.
Frequency of observable characteristics
Base sequence of DNA
Base sequence of mRNA
Amino acid sequence
Define species
A group of organisms that can interbreed to produce fertile offspring
State what the cell cycle is and outline its stages
cycle of division with intermediate growth periods
interphase
mitosis or meiosis (nuclear division)
cytokinesis (cytoplasmic division)
Explain why the cell cycle does not occur in some cells.
After differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have the ability to divide.
What is the difference between the cell cycle and mitosis
Cell cycle includes growth period between divisions
Mitosis is only 10% of the cycle and refers only to nuclear division
Outline what happens during interphase.
G1: cell synthesises proteins for replication (e.g. tubulin for spindle fibres) and cell size doubles
S: DNA replicates - chromosomes consist of 2 sister chromatids joined at a centromere
G2: organelles divide
State the purpose of mitosis.
produces 2 genetically identical daughter cells for:
growth
cell replacement / tissue repair
asexual reproduction
Outline what happens during prophase.
Chromosomes condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere)
Centrioles move to opposite poles of cell (animal cells) and mitotic spindle fibres form.
Nuclear envelope and nucleolus break down - so chromosomes free in cytoplasm.
Outline what happens during metaphase.
Sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres.
Outline what happens during anaphase.
Spindle fibres contract - centromeres divide
Sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles of cell (look like V shapes facing each other)
Spindle fibres break down
Outline what happens during telophase.
Chromosomes decondense, becoming invisible again.
New nuclear envelopes form around each set of chromosomes - 2 new nuclei, each with 1 copy of each chromosome.
Explain the procedure for a root tip squash experiment.
Place root in hydrochloric acid to halt cell division.
Stain root tip with a dye that binds to chromosomes.
Macerate tissue in water using mounted needle.
Use mounted needle at 45 degrees to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles.
Focus an optical microscope on the slide. Count total number of cells in the field pf view and number of cells in a stage of mitosis.
Calculate mitotic index (no. of cells undergoing mitosis/total no. of cells)
Name 2 dyes that bind to chromosomes
toluidine blue (blue)
acetic orcein (purple-red)
Why is only the root tip used when calculating a mitotic index?
Meristematic cells at root tip are actively undergoing mitosis.
Cells further from root tip are elongating rather than dividing.
Suggest how cancer treatments control the rate of cell division
Disrupt the cell cycle:
prevent DNA replication
disrupt spindle formation - inhibit metaphase/anaphase
Targets rapidly dividing cells like cancer cells, however, could also damage healthy cells
How do prokaryotic cells replicate?
Binary fission:
DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm.
Cell elongates, separating the 2 DNA loops.
Cell membrane contracts and septum forms.
Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids.
Why are viruses classified as non-living?
They are acellular: no cytoplasm, no metabolism and cannot self-replicate
Outline how viruses replicate.
Attachment proteins attach to receptors on host cell membrane.
Enveloped viruses fuse with cell membrane or move in via viruses inject DNA/RNA.
Host cell used viral genetic information to synthesis new viral proteins / nucleic acid.
Components of new viral particle assemble.
How do new viral particles leave the host cell?
Bud off and use cell membrane to form envelope
Cause lysis of host cell
Why is it so difficult to develop effective treatments against viruses?
Replicated inside living cells - difficult to kill them without killing host cells.
Describe the process of crossing over.
Homologous pairs of chromosomes associates, forming a bivalent
Chiasmata form
Equal lengths of non-sister chromatids / alleles are exchanged
Producing new combination of alleles (recombinant)
adenine
One of the four nucleotide bases in DNA and RNA.
anticodon
A sequence of three nucleotides on tRNA that is complementary to a specific codon on mRNA during translation.
base
A nitrogenous molecule that forms part of a nucleotide in DNA and RNA.
chromosome
A structure made of DNA and proteins that carries genetic information in the nucleus of a cell.
codon
A sequence of three nucleotides on mRNA that codes for a specific amino acid during translation.
complementary base pair
A pair of nitrogenous bases in DNA that are connected by hydrogen bonds, such as adenine-thymine and guanine-cytosine.
cytosine
One of the four nucleotide bases in DNA and RNA.
DNA
Deoxyribonucleic acid, a molecule that carries genetic instructions for the development, functioning, growth, and reproduction of all known organisms.
double helix
The twisted ladder shape formed by two strands of DNA held together by complementary base pairing and hydrogen bonds.
gene
A segment of DNA that contains the instructions for building one or more molecules of RNA or protein.
genetic code
The set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins by living cells.
guanine
One of the four nucleotide bases in DNA and RNA.
mRNA
Messenger RNA, a type of RNA that carries the genetic information from DNA to the ribosome for protein synthesis.
methionine
An amino acid that serves as the start codon in protein synthesis.
mutation
A change in the DNA sequence that can lead to alterations in protein structure or function.
nucleotide
The building block of DNA and RNA, consisting of a sugar molecule, a phosphate group, and a nitrogenous base.
ribosome
A cellular structure that carries out protein synthesis by translating mRNA into amino acid sequences.
RNA
Ribonucleic acid, a molecule that plays a role in various biological processes, including protein synthesis.
stop codon
A sequence of three nucleotides on mRNA that signals the end of protein synthesis.
thymine
One of the four nucleotide bases in DNA.
transcription
The process by which the genetic information in DNA is copied into RNA.
translation
The process by which the genetic information in mRNA is used to synthesize proteins.
tRNA
Transfer RNA, a type of RNA that carries amino acids to the ribosome during protein synthesis.
uracil
One of the four nucleotide bases in RNA.
nucleus
A membrane-bound organelle that contains the cell's DNA and controls cellular activities.
chromatin
The complex of DNA and proteins that make up chromosomes.
histone proteins
Proteins that help package DNA into a compact and organized structure.
nuclear pore
A protein-lined channel in the nuclear envelope that regulates the passage of molecules between the nucleus and the cytoplasm.
rough endoplasmic reticulum
A network of membrane-bound tubes and sacs studded with ribosomes, involved in protein synthesis and processing.
vesicle
A small, membrane-bound sac that transports and stores substances within a cell.
golgi apparatus
An organelle involved in the processing, packaging, and secretion of proteins and lipids.
3' and 5' ends of DNA
The two ends of a DNA strand, with one end having a free 3' hydroxyl group and the other end having a free 5' phosphate group.
promoter region
A specific sequence of DNA that initiates the transcription of a particular gene.
TATA box/region
A DNA sequence that helps position RNA polymerase to initiate transcription.
template strand
The DNA strand that is used as a template during transcription to synthesize a complementary RNA molecule.
transcription factors
Proteins that bind to DNA and help regulate the transcription of genes.
RNA polymerase
An enzyme that catalyzes the synthesis of RNA from a DNA template during transcription.
intron
A non-coding region of DNA that is transcribed into RNA but is removed during RNA processing.
exon
A coding region of DNA that is transcribed into RNA and is retained in the final processed RNA molecule.
peptide bond
The covalent bond formed between two amino acids during protein synthesis.
polypeptide
A chain of amino acids linked by peptide bonds, forming part of a protein molecule.
primary structure
The linear sequence of amino acids in a protein.
secondary structure
The local folding of a polypeptide chain into regular structures, such as alpha helices and beta sheets.
tertiary structure
The overall three-dimensional shape of a protein, determined by interactions between amino acid side chains.
quaternary structure
The arrangement of multiple polypeptide chains in a protein complex.
epigenetics
The study of changes in gene expression or cellular phenotype that do not involve changes to the underlying DNA sequence.
methylation
The addition of a methyl group to DNA, often associated with gene silencing.
acetylation
The addition of an acetyl group to a protein, often associated with gene activation.
pluripotent stem cells
Stem cells that have the potential to differentiate into any type of cell in the body.
cell differentiation
The process by which cells become specialized in structure and function.
Give an example of immunology sequencing.
The chimp antibodies might recognise the human proteins , but not mouse ones.
What is classification?
The sorting of organisms into groups.
What is the binomial system?
The system to name species.
Give an example of DNA sequencing used to classify organisms.
Humans and chimps share 94% in their genomes.
What is phylogeny?
It is the study of evolutionary history of groups of organism. it looks at who shares common ancestors, and who is more closely related to who.
What does it mean if archaea and eukarya share a more recent ancestor than bacteria?
It means that archaea and eukarya are more closely related.
What is a species?
A group of organisms that can interbreed to produce fertile offspring. They are similar in appearance, generics, physiology, anatomy and biochemistry.
How are courtship behaviours used to classify organisms?
Chemical release, sound, visual display, building, dancing are all species specific. It allows recognition and successful breeding between the same species. It ensures compatible gametes.
