D2 Flashcards
Cytokinesis
Splitting of the cytoplasm to create two daughter cells from one parent cells (last step of cell division after mitosis)
Cleavage furrow
region of pinching @ the centre/equator of the cell that occurs in the early stages of cytokinesis, achieved using a ring of contractile proteins
Cell plate
layer of fused vesicles at the equator of a plant cell during cytokinesis, which will eventually form a new cell wall
sister chromatids
two identical copies of a chromosome attached to each other by proteins. they are created after chromosomes replicate
DNA condensation
processing of compacting DNA tightly around histones, forming nucleosomes, and then linking said nucleosomes together
cell cycle
series of events that lead up to cell division (including interphase and stages of division)
interphase
stages prior to division in which growth, DNA replication and preparation occur
what percentage of the cell cycle is spent in interphase
90%
cell proliferation
when there is a rapid increase in the number of cells i.e. rate of cellular divison exceeds rate of cell death
what is the name for prokaryotic cell division
binary fission
what happens in binary fission
circular DNA is replicated and separated
what type of genetic material does mitosis occur for
when DNA is linear and contained in the nucleus
How does cytokinesis differ between plant and animal cells?
In animals, it is quite a straightforward process. The outside of the cytoplasm pinches to form the cleavage furrow (made out of contractile rings). In plants, the cell plate forms from merging vesicles
Examples of cytokinesis in which the cytoplasm is not equally divided
Oogenesis
Budding
Why does oogenesis result in uneven division of the cytoplasm?
Cytoplasm divides unequally to create one large egg cell (with lots of organelles and cytoplasm) and three polar bodies (that have minimal cytoplasm)
Why does budding result in uneven division of the cytoplasm?
Nucleus divides evenly to form two identical nuclei but the new daughter cell only takes a small amount of the cytoplasm. This daughter cell can then grow later.
Structure of sister chormatids formed by DNA replication
two identical strands held together by a centromere and multiple cohesin looops. during mitosis, spindle fibres will attach to kinetichore proteins in order to break them apart
What does DNA replication form?
sister chromatids
What occurs in G1?
Cell grows in size and accumulates important materials (e.g. increased proteins, increased nucleotides)
What occurs in S phase?
DNA is replicated, creating sister chromatids
What happens in G2 phase?
Further cell growth, further replication of important organelles. Microtubules begin to form visible centrosomes
Purposes of cell proliferation
growth, replacement, repair
examples of rapid mitosis for growth in plant cells
Plan meristem cells rapidly divide then specialise
examples of rapid mitosis for growht in animal cells
Having grown from a zygote, an animal embryo in the late stages undergo rapid unspecialised division and then specialisatin
examples of cells that are frequently replaced by mitosis
skin cells, as layers are constantly growing the next layer of skin cells
when does mitosis occur for repair
following injury rapid cell replacement occurs
How does cytokinesis typically occur in an animal cell?
Contractile proteins (actin and myosin) migrate to form a ring within the cell. This creates a cleavage furrow, which then eventually splits the cell
How does cytokinesis typically occur in a plant cell?
A line of vesicles merge in the centre of a plant cell. Once merged, this forms a temporary cell plate.
These vesicles contain cellulose within them, which eventually become the cell wall. The two phospholipid outsides of the vesicle become the new cell membrane for the daughter cells.
What are the two DNA changes that occur before cell division?
- DNA replication to form sister chromatids
- DNA condensation into short wide chromosomes
Why is DNA loosely coiled normally?
This is the optimal state for transcription
Process of DNA condensation
The DNA is originally loose (for transcription). It is then wrapped around histones to form a nucleosome. These nucleosomes then stack and coil, forming visible chromosomes
Product of DNA condensation
Short, wide and visible chromosomes
What is the cell cycle
events that cells go through to divide
all stages of the cell cycle
G1, S, G2, prophase, metaphase, anaphase, telophase and cytokinesis
OR
interphase, mitosis, cytokinesis
Which part of the cell cycle do heart and brain cells always remain in?
G0 (not part of cell cycle!!)
Where does normal cellular activity occur (part of cell cycle)?
G0
What part of the cell cycle can cells exit to enter G0?
During G1
How do cells in G0 re-enter the cell cycle?
If signalled to engage in growth, repair or replacement
How quickly can white blood cells replicate?
Within 10 hours
What occurs during mitosis?
Division of the nucleus
What is the metaphase plate?
imaginary plate that runs along the centre of the cell (i.e. midpoint)
Centrosomes
Organelle composed of two centrioles, which form spindle fibres to attach to chromosomes
synonyms for centrosomes
microtubule organising centres (MTOCs)
purpose of kinetichores?
have microtubules attach
what are kinetochores?
protein structures that form at the centromere of each chromatid. microtubules can attach
what is the mitotic index?
calculation that quantifies the proportion of cells currently dividing i.e. no. cells in mitosis / total no. cells
what can a high mitotic index indicate?
tissue dividing too rapidly -> cancer
order of phases in mitosis
prophase, metaphase, anaphase, telophase
Key features of interphase
DNa is in its loose form called chromatin, which allows for protein synthesis. No chromosomes are visible.
During this phase, DNA replication occur.
What happens in prophase?
Nuclear membrane dissolves/migrates as vesicles
DNA condenses to become visible chromosomes
Centrosomes form and begin developing microtubules.
What happens in metaphase?
Microtubules attach to each end of the centromere (of each sister chromatid) at the kinetochore.
Motor proteins (which exist between microtubules) move the chromosome, aligning them at the centre of the cell. This alignment occurs because both ‘ends’ of chromatids are being pulled in opposite directions by motor proteins.
What happens in anaphase?
Motor proteins continue to pull apart sister chromatids. Eventually, this migration of centromeres puts enough pressure on cohesin loops to break them, separating chromatids at the centromere. Kinetochores shorten microtubules (by breaking off tubulin subunits), which pulls the chromosomes to the poles.
What happens in telophase?
Nuclear membrane reforms.
DNA decondenses into loose chromatin. Cell elongates in preparation for cytokinesis.
The pinching of the membrane begins cytokinesis
What is between two microtubules?
Motor proteins, which help pull microtubules towards opposite poles.
How do motor proteins interact with microtubules to move chromatids in anaphase?
Motor proteins (between two microtubules) ‘walk’ along, separating sister chromatids. This creates the required tension to break cohesin loops.
Mitosis
the process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division.
Gametes
specialised cell made purposefully for sexual reproduction.
how many chromosomes do gametes have?
23 (half the normal number) i.e. haploid
what is reduction division
refers to the fact that in meiosis, cell division causes genetic material to halve in its daughter cells
what is the product of two gametes?
zygote
homologous chromosomes
pair of the same chromosomes. same genes in the same positions but different alleles
bivalent
when homologous chromosomes each have sister chromatids join together, so that inner chromatids overlap at the chiasma. They break at the chiasma and swap genetic material.
Diploid nucleus
Two of each chromosome (46 total)
Haploid nucleus
One of each chromosome (23 total)
What type of cells are diploid?
all somatic cells
What type of cells are haploid?
all gametes
difference between meiosis I and meiosis II
Meiosis I: chromosomes line up in homologous pairs in metaphase.
Meiosis II: sister chromatids line up to be separated
Similarities between mitosis and meiosis
1 DNA replication occurs.
PMAT format
Differences between mitosis and meiosis
Which cells it occurs in
Number of division
What it forms
Whether chromosomes interact
Purpose
Product of mitosis
Two genetically identical diploid daughter cells, each with a full chromosome set
WHat cells does meiosis occur in
Germ cells (which become gametes)
What cells does mitosis occur in?
Somatic cells
Process of meiosis
1 DNA replication
2 divisions (i.e. 2 x PMAT)
Product of meiosis
Four genetically unique haploid daughter cells
Do homologous chromosomes interact in mitosis?
No.
How do homologous chromosomes interact in meiosis?
Homologous chromosomes join together to create bivalents and crossing over occurs
Purpose of meiosis
Sexual reproduction
Process by which homologous chromosomes become bivalents
Synpasis
What happens to chromosomes in DNA replication?
Chromosomes undergo DNA replication to form chromosomes with two sister chromatids connected by a centromere and cohesin loops. These sister chromatids have identical alleles.
When do homologous chromosomes first interact in meiosis?
Prophase I, in which they undergo synapsis to form bivalents, connected at the chiasma.
What is different between homologous chromosomes?
Alleles. However, same genes
What cells undergo meiosis?
Diploid germ cells
Stages of Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Stages of Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
What occurs in Prophase I that is specific to meiosis?
Synapsis forms bivalents and crossing over occurs.
What occurs in Metaphase I that is specific to meiosis?
Line up as homologus pairs, with random orientation of each pair on either side
What occurs in Anaphase I that is specific to meiosis?
Separation of homologous chromosomes
What is the product of meiosis I?
Two haploid germ cells
What happens after Telophase I
Prophase II (does not re-enter interphase!)
What part of meiosis is most similar to mitosis?
Meiosis II
What happens to the nuclear membrane in Prophase II?
Nuclear membrane dissolves
What happens to the nuclear membrane in Telophase I?
Nuclear membrane reforms
Name of process that creates sperm cells
Spermatogenesis
Name of process that creates egg cells
Oogenesis
Recombinant chromatids
Chromatids that have gone through crossing over and now contain new combinations of genetic material
Random orientation
In metaphase, it is random which side each chromosome/chromatid goes on
Non-disjunction
when chromosomes fail to separate, meaning that spindle fibres do not attach to one of the centromeres
what have the spindle fibres failed to do if non-disjunction occurs?
Attach to centromere
How does crossing over contribute to genetic variation?
Creates new combinations of alleles, which work together to create new phenotypic variation
How does random orientation contribute to genetic variation?
Alters combinations of alleles that are inherited, leading to greater uniqueness between offspring and thus, greater genetic variation
What role does meiosis play in natural selection?
New phenotypes can be made (via crossing over and random orientation)
Cause of Down Syndrome
Trisomy 21 (due to non-disjunction of chromosome 21)
characteristics of down syndrome
Developmental condition characterised by hearing, heart and vision concerns and intellectual disability
Why does non-disjunction increase with maternal age?
As age increases (i.e. leave biological fertile window), it becomes less of a priority for checking spindle fibres. This causes errors to go unchecked, which contributes to increased number of gametes with errors
What happens to the location of the chiasma with every round of meiosis?
Location changes
What is crossing over?
Breaking and exchanging DNA between homologous chromosomes
What is the name for chomatids that have not been affected by crossing over?
Parental chromatids
Does random orientation create new alleles?
No, just new phenotypes
Number one cause of miscarriage
Non-disjunction
Which part of meiosis does non-disjunction most often occur in?
Anaphase I, due of cohesin loops
If non-disjunction of Chromosome 21 occurs in Anaphase I, what cells will it produce?
2 x trisomy 21
2 x monosomy 21
Euploidy
a term used in genetics to describe when an organism or cell has the correct number of chromosomes
What happens if non-disjunction occurs in Anaphase II for Chromosome 21?
1 x Trisomy 21
1 x Monosomy 21
2 x euploidy
What contributes to genetic variation?
Meiosis -> creates new combinations of alleles through crossing over and random orientation
Mutations -> new alleles
Sexual reproduction
Cyclins
Groups of proteins that will control whether a cell will progress through the cell cycle, by binding to Cyclin-Dependent Enzymes
Cyclin-dependent enzymes
Enzymes that cyclin proteins bind to (and are inactive without cyclin being bound)
Checkpoints
Multiple times udring cell cycle where events will stall until certain requirements are met
Cancer cells
Cells that undergo extremely rapid and uncontrolled reproduction with very little or improper differentiation
Proto-oncogenes
Genes that stimulate or cause cell divison
What is a proto-oncogene called if mutated and not functioning properly?
Oncogene
Oncogene
Proto-oncogene mutated and not functioning properly
Tumour suppressor genes
genes that code for proteins that play a role in slowing, pausing or stopping the cell cycle
benign tumour
tumour contained to a single part of the body and that is not spreading
metastasis
process when cells from a primary tumour break and enter the bloodstream, and cells travel via the blood to a new location + start growing a new tumour
relationship ebtween cyclin and Cyclin-Dependent Kinases?
CDK enzymes rely on cyclin binding to become activated
significance of the G0 stage
stage where cells do not replicate or progress through the cycle i.e. just perform normal functions
how can a mutation of a proto-oncogene lead to tumour formation
mutated to promote cell division when conditions are not appropriate or in the absence of check points, which therefore overpromotes divion
how can a mutation of a tumour suppressor gene lead to tumour formation
mutation compromises the ability of this gene to stop cell division in the event of DNA damage or when the cell type does not need division -> cannot stop cell division -> constant cell division
difference between primary and secondary tumour
primary = first cluster of cancerous cells that form due to mutation
If the primary tumour metastasises and invades other healthy tissue, the new tumour formed is called the secondary tumour
Are CDKs activated by the same cyclin?
No, CDKs are activated by cyclin specific to its phase e.g. growth, DNA checked, replication, spindle fibres, etc.
What produces G1 cyclin?
cell growing
what happens if not enough G1 cyclin is produced?
The cell goes into G0
What releases G1/S cyclin?
DNA checks being passed
What releases S cyclin?
DNA replication
what releases M cyclin?
spindle fibres being checked
how many checkpoints are there in the cell cycle?
4
What happens when proto-oncogenes are expressed normally?
They promote/accelerate cell division
What are the ways proto-oncogenes can be modified to form oncogenes?
CDK mutates to be active all the time
Gene mutates to create cyclin all the time
When is the tumour suppressor gene most active?
Most active in S Phase and M spindle fibres phase
What is the process of a secondary tumour being formed?
Healthy cells experience a mutation and thus; a primary tumour is formed. If no intervention occurs, these cells become vascularised at some point and thus, metasise into the bloodstream and arrive at another part of the body. The tumour cells then form a secondary tumour
Gene regulation
Process of controlling timing, location and amount in which genes are expressed in an organisation
Phenotype
physical trait that is the result of specific proteins that an individual has due to their gene expression
mRNA degradation
use of enzymes to break up mRNA to nucleotides for recycling e.g. removing poly A tail
exonucleases
enzymes that break down nucleic acids by removing individual nucleotides
epigenesis
process of changing the phenotype of a cell without altering its genotype/pattern of gene expression that causes cells to change parts of their genome to become specialised
epigenetic tags
chemical modifications to DNA in order to flag part of the genome to guide its regulation
DNA methylation
process of adding a -CH3 methyl group to a DNA nucleotide as an epigenetic tag
promoter
region ahead of coding bases that is a binding site for transcription factors which then allow RNA Polymerase to bind
transcription factors
proteins that regulate transcription that can eiteher act as ‘activators’ or ‘silencers’
enhancer region
having binding sites that activators can bind to, allowing DNA to form a loop,which allows activators to interact with transcription factors at promoters. this ultimately increases the rate of transcription
what do activators bind to to initiate transcription?
activators bind to enhancer to promote/accelerate transcription
what do repressors bind to to prevent transcription?
repressors bind to silencers
how is the length of the poly A tail a form of gene regulation
longer tail = more time before enzymes break off adenosines -> more proteins are made
what role does DNA methylation play in regulating transcription?
turn off expression of a gene by not allowing binding of necessary transcription factors
Where does the majority of gene regulation occur?
Earlier in the process, so that energy is not wasted
What binds to an enhancer site?
Activator transcription factor
What binds to a silencer site?
Repressor transcription factor
What is the effect of a repressor transcription factor binding to a silencer site?
Slows/stops the rate of transcription
What is the effect of activator transcription factors binding to an enhancer site?
Increases rate of transcription
What do transcription factors allow the regulations of?
careful regulation of amount and timing of transcription
If mRNA is present in the cytoplasm, what will occur?
(generally) translation
What is one way to regulate translate?
Regulate rate of mRNA degradation
What can exonucleases do to degrade mRNA?
Decap the GTP cap
Deadenylation
Both of which need to occur to eventually break down mRNA
What happens if the activity of exonluceases increases?
More mRNA degradation
Decreased mRNA lifespan
What two processes must occur before exonucleases can break down mRNA?
Removal of GTP cap
Removal of poly A tail
What is the most common use of DNA methylation?
Turn genes off
How can DNA methylation turn genes on?
Binding to a silencer region
What do methyl groups bind to?
Histones (to block a group of genes)
DNA (to regulate a specific genes, usually at the promoter to stop transcription factors binding)
what is the duration of methylation?
usually permanent
Two outcomes of DNA methylation
Cell specialisation
Cellular response to external environment
When does DNA methylation occur first?
During utero and then throughout lifetime
What happens if a methyl group binds to a promoter?
The transcription factor cannot bind and thus, this gene is not transcribed
Genome
All the genes an organism has
Transcriptome
All mRNAs a cell can produce
What is one of the reasons the transcriptome is larger than the genome?
Alternate splicing, different Poly A tail lengths, etc
Proteome
All proteins an organism can produce
Why is the proteome larger than the transcriptome?
Modifications
Epigenetic inheritance
when epigenetic tags are passed from a parent to offspring
primordial germ cells
diploid cells that will go through meiosis to form gametes
epigenetic reprogramming
process of removing epigenetic tags during the formation of primordial germ cells
imprinted genes
genes that are silenced only in one type of gamete
differentially methylated regions
genome regions with different methylation patterns across samples
operon
group of several related genes that share a single promoter and thus, allows groups of genes to be turned off or on
what role can the environment play in the formation of epigenetic tags?
can change gene expression to optimise coping with an external stressor
explain specifically how air pollution has been linked to methylation
two chemicals (nitrous oxides and hydrocarbons) have been shown to decrease DNA methylation acorss the genome and thus, increase the expression of proteins related to the immune system, leading to issues such as asthma and allergies
how do the differences between ligeons and tigers relate to patterns of epigenetic inheritance?
maternal and paternal lions imprint genes differently. male imprinting favours larger offspring by not silencing a gene that promotes growth, whilst female imprinting silences this gene and therefore does not express it.
male lion + tiger = liger
female lion + tiger = tigeon
how have monozygotic twin studies been helpful to understand methylation?
despite having identical DNA sequences, idential twins have different phenotypes and therfore, indicate how methylation patterns can explain phenotypic differences
when is the most significant time for external influence to change epigenetic inheritance?
during pregnancy
How can epigenetic inheritance be intergenerational?
If a parent is exposed to an external stressor (esp. during pregnancy), their gametes will experience different methylation patterns. The children will then carry this pattern and it will continue
Eukaryote example of external regulators of gene expression
Glucose regulates insulin production
How does glucose regulate insulin production?
glucose causes the activation of a transcription factor, by binding to it. this allows the insulin gene to be expressed, meaning that insulin is made. this ultimately lowers the glucose level, causing the glucose to be removed from the transcription factor
prokaryote examples of external regulators of gene expression
lactose activates the lac operon. the lactose binds to the repressor on the operator which allows RNA Polymerase to express the genes. this means that the lactose is broken down, including in the repressor
Solvation
interaction between solvent and solute
dynamic equilibrium
when particles are evenly spread out and net water movement is 0
crenation
shrinking of a cell (usually for animal cells)
contractile vacuole
adaptation in unicellular aquatic organisms to prevent swelling, as it collects water from the cytoplasm + periodically empties it into the environment
hypertonic
environment with higher solute concentration than other environment
hypotonic
environment with lower solute concentration than other environment
isotonic
environment with same solute concentration as other environment
