Cell Cycle, Cellular Ageing and Cell Death, Regulation of Gene Expression Flashcards
What is a purpose of DNA?
Dictates cells’ structure and function
What are a major source of mutations?
Errors in copying DNA during DNA replication
Why do cells progress through the cell cycle?
To undergo mitosis
What are the names of controlled and uncontrolled cell death?
Apoptosis: controlled cell death
Necrosis: uncontrolled cell death
What are the definitions of the following terms?
Gene
Allele
Exon
Intron
Genotype
Phenotype
Mutation
Gene: functional region of DNA that codes for a sequence of RNA
Allele: individual variant of a gene
Exon: portions of a gene product that are removed via RNA splicing
Intron: portions of a gene product that are retained following RNA splicing
Genotype: the genes (and alleles of them) in a cell/organism
Phenotype: physical features of an organism as of its genotype
Mutation: changes in the genetic sequence (order of base nucleotides)
How can RNA be derived from DNA?
Transcription
What are the multiple forms of RNA and their function/role?
Messenger RNA (mRNA): translated to produce polypeptides
Transfer RNA (tRNA): involved with translation
Ribosomal RNA (rRNA): major part of ribosomes
Short interfering and micro RNA (siRNA and miRNA): inhibit translation of complementary mRNA
How do miRNA and siRNA inhibit translation?
Bind to complementary mRNA and prevent the ribosome from binding and allowing translation to occur
Marks mRNA for degradation, therefore there is no protein synthesised
What is the function of miRNA and siRNA?
To not allow too much mRNA to be present, so as to have no extremes
Reduces likelihood of mutations
What is all gene expression due to?
Dictating factors such as methylation, acetylation and transcription factors
What is fine tuning?
Nuanced activity
Why may a cell have cell-signalling?
To prevent the translation of unnecessary proteins (hence miRNA and siRNA) as cell has multiple things in multiple directions
What is the meaning of “one gene, one protein”?
One gene codes for one protein and determines its function
Why is there controversy regarding “one gene, one protein”?
Not strictly true as multiple proteins may come from one gene as not all triplets read for the gene
Splicing causes certain exons to be lost or kept e.g., antibodies
What is a codon?
3 base sequences
Read in sets of three
What are mutations?
One source of genetic variation
Do mutations require a response to occur?
No, they occur randomly
What happens in a substitution mutation?
One base is replaced with another
What are the different types of substitution mutations?
Silent: new code for same amino acid, so the protein remains the same
Missense: new code changes the amino acid
Nonsense: new code is a STOP codon and stops the protein from being produced
Are the effects of missense substitution mutations alarming?
Effects are dependent on the role of the amino acid
E.g., a linking amino acid will not change as much
When will a missense substitution mutation have an alarming effect?
If an amino acid responsible for the protein’s structure is changed
What is a frameshift mutation?
The triplet code is disrupted, so all amino acids after the mutation change
What are the different types of frameshift mutations?
Addition: a new base is added, shifting the rest forward relative to the reading frame
Deletion: a base is removed, pulling the rest back relative to the reading frame
Why are frameshift mutations problematic?
If a set of 3 nucleotides (new codon) starts a nucleotide after the frameshift mutation, then the amino acids will change
How can frameshift mutations have little to no effect on a protein?
Frameshift mutations may:
Occur at the ends of genes
Occur in introns
Occur outside of genes
What two groups can cells be divided into?
Somatic and germline
Is there a single genome of the whole body?
No, each cell has its own DNA
Which type of cells are defined as germline cells?
Gametes- cells that have genes that can be passed on
What are the products of gametes?
A person’s “normal” DNA
What are germline mutations?
Mutations and genetic variation in germline cells- these mutations/genetic variations can be passed through families
What happens if there is a mutation in an embryo as of the germline cells that produced it?
The resulting embryo will have that germline mutation throughout all its cells
What are somatic cells?
Any cell in an organism apart from the reproductive (germline) cells
What happens if there is a mutation in a somatic cell?
Then only the mutated cell will be effected and this mutation won’t be passed on
Can somatic mutations be inherited?
No
What are the effects of embryonic mutations?
All the cells (including somatic cells) are effected
How can a mutation spread from an affected somatic cell?
The mutation will be passed onto the cells it divides into
How does cancer develop?
From a series of mutations and changes in a stomatic cell
How can a germline mutation affect a zygote’s somatic cells?
All the cells will have the mutations, as the zygote has the mutation
Zygote continues to divide into foetus
What can germline mutations cause?
Genetic disorders, as it is the change of DNA over time
Can also predispose affected individuals to other conditions such as cancer
What is an example of a germline mutation?
Mutation in the BRCA-1 gene or BRCA-2 gene can lead to breast cancer
Why do cells divide?
Growth: from fertilised egg cell to adult, or for subsequential growth, e.g., muscles
Maintenance: replace dead/injured cells
How can cells divide?
By mitosis, however gametes are (partially) produced by meiosis
Which cells don’t generally divide?
Adult cells, like neurones, as they are fully matured
Why do some cells divide then stop?
They will only divide when triggered, such as when a tissue is damaged or a cell dies
What are some examples of cells that continuously proliferate (replicate) and why do they do this?
Hair follicles and red blood cells, as to replace things that have broken down
Why is proliferation important regarding embryogenesis?
Early development is characterised by the embryonic cells’ rapid proliferation
These cells then differentiate
When the cells differentiate, the rate of proliferation usually decreases
What other process is proliferation important in?
Maintenance of adult tissue homeostasis:
Matured cells lose the ability to proliferate, however there are some cells that proliferate but only when triggered e.g., replacing damaged cells
What affects proliferation?
Environmental conditions: pH, nutrients, temperature and oxygen
Interactions with other cells and signaling molecules
Intracellular signaling
What is true about all body cells?
They can broadly be divided into germline and somatic cells
Why does a germline cell require both mitosis and meiosis?
Meiosis ensures that the DNA is halved
Mitosis is to produce the cells that precede the germline production
E.g., spermatogonia need to undergo mitosis to enable spermatozoa to keep being produced
Why can somatic cells not be passed onto the offspring?
They don’t produce gametes
What is the cell cycle?
When a cell divides via a series of stages
What are the stages of the cell cycle?
G1
S phase
G2
M phase
(G0- resting phase)
What are the sub-stages of the M phase?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
What is are the purposes of the G1 and G2 phases?
They are gap/growth phases and also incorporate checkpoints to see if the cell is capable of being replicated
What roles do the G1 and G2 phases have?
G1: Preparation for DNA synthesis (S phase), replication
G2: Preparation for cell division (M phase), doubles in size
What would happen if damage to the DNA is detected in the dividing cells?
The cell will not progress through the cell cycle until the DNA damage has been fixed
If the damage cannot be fixed, then the cell will undergo apoptosis
What occurs during S phase?
DNA replication:
DNA helicase separates DNA strands by breaking hydrogen bonds between them
DNA polymerase catalyses the addition polymerisation of the DNA nucleotides
How do the new nucleotides form the new DNA strands?
New nucleotides are added to the 3’ (“3 prime”) end of the new strand. New nucleotides are attached via their 5’ (“5 prime”) end
Leading strand is made continuously, following helicase
Lagging strand is made in fragments in the opposite direction to helicase action, then combined by DNA ligase
Where does DNA polymerisation occur?
The length of the chromosome
How is the cell cycle controlled?
Checkpoints
How are checkpoints useful?
Allow for processes (like mitosis) to occur in fixed time intervals
What influences the checkpoints?
Cell cycle events and the external environment
How is DNA presented in the S-phase?
As two identical chromatids
What occurs in the S-phase?
Chromosomes undergo replication
New DNA is synthesised- therefore a duplicate chromosome is formed
Chromosome is only visible during division
After replication, each chromosome is composed of two identical chromatids, and chromatids are joined together at the centromere
What is the purpose of the M-phase?
How the cell physically divides to produce two genetically identical daughter cells
What is the main process that occurs in the M-phase?
Mitosis- due to the cell’s nucleus dividing
What are the stages of mitosis that the cell’s nucleus undergoes?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
What occurs during cytokinesis?
The cell’s cytoplasm divides to form the two separate daughter cells
What occurs to the DNA and nucleus during prophase?
The chromosomes condense and are visible and threadlike
Nuclear membrane and nucleoli disappear
What occurs outside the nucleus during prophase?
Mitotic spindle begins to form
Mitotic spindle contains centrosomes and microtubules forming aster (star shape)
Centrosomes move away from each other
What occurs during prometaphase?
Nuclear envelope fragments
Microtubules attach to the chromatids at the kinetochores
Other microtubules interact connecting from different poles
What occurs during metaphase?
Centrosomes are now at opposite poles of the cell
Chromosomes are lined up on the metaphase plate
All chromosomes are attached to each of the poles
What occurs during anaphase?
Connection between the chromatids at the centromere is cleaved
Each chromatid is now a daughter chromosome
Chromosomes are pulled to opposite poles as cell elongates
What indicates that anaphase is over?
When the chromosome reaches the poles
What occurs during telophase and cytokinesis?
Two daughter nuclei form
Nuclear envelope forms, nucleolus appear and cytoplasm divides
What happens to the DNA during telophase and cytokinesis?
Chromosomes become less dense, and so less visible
What else occurs during telophase and cytokinesis?
Contractile rings from- contain actin, myosin, and various other proteins and structures
Cytoplasm divides into two
Creates two genetically identical (diploid) daughter cells
Is cytokinesis apart of mitosis?
No, as cytokinesis refers to the division of the cell’s cytoplasm. Mitosis is the division of the cell’s nucleus
What occurs during the M-phase?
Two cells, each with the same number of chromosomes as the original cell
Cell moves into G1- start of interphase
What is the importance of the process of meiosis?
Necessary for the function and production of gametes
What is a key difference between mitosis and meiosis?
The gametes (sperm and egg cells) that are produced are haploid, and so have one chromosome from each pair. However, mitosis produces diploid cells
How is meiosis a form of genetic variation?
Fusion with different gamete for mixing of gene combinations
Each gamete having a different combination of the parent’s genes
Recombination, resulting in new chromosomes
What is the key principle of meiosis?
DNA is replicated once but the cell divides twice
What occurs during meiosis l?
Homologous (paired) chromosomes are separated from each other but remain intact (sister chromatids are still attached to each other)
What occurs during meiosis ll?
Sister chromatids on each chromosome are separated into the new cells
Are there any similarities and/or differences between mitosis and meiosis?
Yes, the processes involved are very similar apart from the processes occurring twice in meiosis
What are some other key differences between mitosis and meiosis?
Prophase l: Crossing over between chromatids of paired chromosomes occurs, increasing genetic variation
Metaphase l: Homologous chromosomes are attached to opposite poles of the cell. Independent assortment means each division results in a different combination of chromosomes in each cell
Anaphase l: One chromosome of each pair is pulled to each end without breaking the centromeres
What happens at the end of meiosis l?
There are two cells with unpaired chromosomes consisting of two sister chromatids joined together (unlike mitosis, which results in two cells with paired chromosomes and single chromatids)
What occurs during meiosis ll?
Follows similarly to mitosis:
Centromeres are broken during anaphase, which results in the sister chromatids separating from one another to go into the new cells
What are the two main forms of cell death, and how can they be described?
Apoptosis: Controlled process
Necrosis: Uncontrolled process
What occurs during apoptosis?
A cell will “self-destruct” if triggered by events such as DNA damage
Self-destructs in a controlled manner, and makes its components available for other cells to use
What occurs during necrosis?
A cell cannot self-destruct in a controlled manner, as it is too heavily damaged, and so falls apart in a disordered manner
How can the events of apoptosis be described simply?
The cell is triggered to undergo apoptosis and so begins to shrink (webbing splits)
The cell breaks into apoptotic cell bodies, called plebs
How can the events of necrosis be described simply?
The cell is too damaged to undergo apoptosis and so begins to swell and undergoes necrosis
Leakage of the cell content occurs as the cell membrane is ruptured
