Topic 3 Cell biology Flashcards
Compare and contrast the structure of the two categories of cell: eukaryotic and prokaryotic cell
eukaryotic has membrane bound organelles, prokaryotic does not.
Eukaryotic has cellulose cell walls, prokaryotic has peptidoglycan cell walls.
Eukaryotic has Linear DNA, Prokaryotic has circular DNA.
Both have cytoplasm
Both are surrounded by a cell membrane.
Describe the structure and function of a nucleus
made of nucleolus, nuclear membrane with nuclear pores and chromosomes, contains dna which is used to produce mRNA for protein synthesis
Describe the structure and function of a nucleolus
produces ribosomes
Describe the structure and function of a ribosome
used for protein synthesis for reading mRNA codons. Found on the rough endoplasmic reticulum
State the function of the flagellum in sperm cells
Movement of the cell through a fluid
State the function of the mitochondria in a sperm cell
Production of ATP energy via aerobic respiration
State the function of the acrosome in sperm cells
releases enzymes used to break down the zona pellucida around the egg cell to allow the sperm cell to reach the cell membrane.
State the function of the haploid nucleus in sperm cells
Contains half of the dna required to form a diploid nucleus inside an egg cell.
State the function of lipid droplets in ovum cells
Provides fuel for respiration to provide energy for cell replication after fertilisation
State the function of the cortical granules inside an egg cell
Move into the zona pellucida which causes the zona pellucida to thicken and harden to prevent polyspermy as acrosome reaction cannot occur.
State the function of the zona pellucida in ovum cells
releases chemicals to attract sperm cells via chemotaxis, acts as a physical barrier after cortical reaction to prevent polyspermy.
State the function of mitochondria in ovum cells
Releases atp energy via aerobic respiration.
State the function of a haploid nucleus in ovum cells
Provides half the dna required to produce a diploid nucleus, ready to be paired with the haploid nucleus of a sperm cell.
Describe the process and function of the acrosome reaction.
Enzymes are released from the acrosome in vesicles, and are transported to the sperm cell membrane where they are released via exocytosis and digest the zona pellucida around the ovum cell.
Describe the process and function of the cortical reaction.
Enzymes released from cortical granules catalyse reactions in the zona pellucida causing it to harden and thicken
Give the term to describe when the haploid nuclei of the ovum and the sperm fuse
Fertilisation
State the definition of the term locus
A point / location on the chromosome
State the definition of the term linkage
Two genes in close enough proximity to one another that crossing over cannot occur between them, so they are linked to each other during meiosis
Explain why males are more likely to suffer from X-linked diseases than females
Because males only have one X chromosome, so they only need one diseased allele to show phenotypes, whereas women could need 2 (if it is a recessive phenotype)
Explain how a stem cell can differentiate into a specialised cell
Under certain conditions, some genes in a stem cell are activated, whilst others are inactivated
mRNA is transcribed from active genes only
This mRNA is then translated to form proteins
These proteins are responsible for modifying the cell (e.g. they help to determine the structure of the cell and the processes that occur within the cell)
As these proteins continue to modify the cell, the cell becomes increasingly specialised
The process of specialisation is irreversible (once differentiation has occurred, the cell remains in its specialised form)
Explain how the lac operon allows differential gene expression in prokaryotes (incl. how the gene is activated and inactivated)
Lac operon is a process. the lactase gene can have a lac repressor bind to it which turns it off when there is no lactose present, when lactose is present and glucose is not
present, lac repressor has a high affinity for lactose and so will bind to lactose instead of lactase gene, freeing the lactase gene allowing mRNA to be transcribed from it.
Define the term stem cell
A stem cell is a cell that has not differentiated into a specific function
Define the term pluripotency
Pluripotent stem cells can differentiate into any cell type apart from extra embryonic cells.
Define the term multipotency
multipotent stem cells can differentiate into a selection of cell types, but not all.
Define the term totipotency
a totipotent stem cell can differentiate into any form of cell including extra embryonic cells
Explain how pluripotent cells are extracted from an embryo
A syringe is used to extract pluripotent cells from the centre of a blastocyst
Give the ethical arguments for and against the use of embryonic stem cells in research/medicine
For: allows development of medicine which could save lives,
embryos have no brain therefore have no feelings.
against: Could be considered killing a child as the embryo has to die for the stem cells to be extracted, essentially prevents a child from coming into existence
State what an induced pluripotent stem cell (IPSC) is
An adult stem cell that has been genetically modified to make a pluripotent stem cell.
Explain why IPSCs are advantageous over embryonic stem cells
Does not require the killing of an embryo, does not cause rejection of the new cells as the cells are from the person they will be used on so they wont have to take immune suppressants.
What effect does methylation of a gene have on its gene expression
Attaches to DNA which attracts proteins which block transcription, therefore reducing its ability to be transcribed, therefore reducing the amount of protein produced in association with the gene, therefore reducing the gene expression.
What effect does histone modification have on gene expression
Weakens association with histone, causing DNA to be less tightly packed, allowing it to be transcribed, causing more of that gene’s protein to be produced, therefore increasing the gene expression.
Give the definition of a tissue
A collection of identical cells
Give the definition of an organ
A collection of different tissues performing a specific function
Give the definition of an organ system
a collection of organs which carry out many different functions e.g digestive tract.
explain how histone modifications result in a spectrum of gene expression
Genes can be entirely repressed if dna has a strong association with histone as dna will be tightly wound. As histone gets more modifications, it becomes more accessible for transcription as the dna becomes more weakly associated with the histone proteins, until eventually the gene is fully activated as the dna is completely unwound.
Explain why genetically identical twins look less similar to eachother with age
Due to epigenetic changes as a result of a change in their environment, causing the switching on and off of certain genes which would affect their phenotype.
