Module 2 Section 6 - Cell Division Flashcards
Smithson & Pyper
What happens in interphase?
- Replication of DNA
- Production of organelles
- Cell elongation
Third stage of the cell cycle
cytokinesis
purpose of mitosis
growth, repair and replacement of cells
G1 (+ what happens in it?)
gap/growth phase 1
cell growth and synthesis of new organelles & proteins
S phase (+ what happens in it?)
synthesis
DNA replication
G2 (+ what happens in it?)
gap/growth phase 2
further cell growth and synthesis of proteins (spindle fibres) needed for cell division
ATP level increases
How is G2 different to G1?
The proteins are more specific in G2 than in G1
ATP level increases in G2 because the proteins (spindle fibres) will need to contract lots during mitosis
M phase
mitosis and cytokinesis
G0 (+ three reasons why cells are in this stage)
Nothing much occurs - it’s the resting phase
- Cells may have already differentiated
- Cells may have become senescent so has damaged DNA
- Cells may have been programmed to die (if they were only needed temporarily)
senescent cell (+ why has it become senescent?)
An old cell - one that has done the max number of divisions e.g. because it has lost lots of bases off the end of the DNA sequence
What cells aren’t in G0? Give at least two examples.
The majority of cells are in G0
Cells that aren’t in G0:
* Stem cells
* Cells that experience lots of wear & tear so need renewing frequently such as skin cells, intestine and stomach lining cells
* Nail cells
Name the phase where DNA replication occurs.
Interphase - more specifically, S phase
What four things are checked for in the G1 checkpoint?
- That enough organelles have been produced that the cell can continue in its cycle
- That there’s enough nutrients (e.g. fats & proteins) to sustain the cell
- That the DNA is undamaged before entering the S phase
- That the cell has grown to a sufficient size
What three things are checked for in the G2 checkpoint?
- That the DNA has replicated without many errors (most important)
- That there are enough protein reserves
- That the cell has grown to a sufficient size
If a cell has DNA with lots of errors, what will it do?
1) Try and repair the DNA damage
2) If there are too many problems, it will perform apoptosis - although this is a last resort
What two things are checked for in the M checkpoint?
- That the chromosomes have lined up at the equator of the cell (so that the sister chromatids will separate half and half)
- That the spindle fibres have attached to all the chromosomes’ centromeres
stages of mitosis in order
PMAT
Prophase
Metaphase
Anaphase
Telophase
Why can it be problematic to describe mitosis in stages?
It’s one continuous process i.e. cells within an organ are all in different stages at one point in time
Describe what happens in prophase in mitosis.
- Chromosomes condense (become visible, shorter & fatter) as the DNA wraps around proteins
- Nuclear envelope breaks down
- Nucleolus breaks up and disappears
- Centrioles move to opposite poles of the cell
- Spindles form - these are networks of protein fibres across the centrioles
Describe what happens in metaphase in mitosis.
- Chromosomes line up in a plane across the equator (middle) of the cell
- Spindle fibres attach to the chromosomes via their centromeres
Describe what happens in anaphase in mitosis.
- The centromere divides - the spindle fibres contract to pull the sister chromatids to opposite poles of the cell, centromeres first
- Cell elongates
Describe what happens in telophase in mitosis.
- Chromatids reach the opposite poles on the spindle
- Chromatids uncoil, becoming long & thin again
- Centrioles disappear
- Nuclear envelopes reform, forming two nuclei
- Nucleolus reforms
- Spindle fibres disintegrate
Where are the chromosomes found after prophase occurs?
Free in the cytoplasm because the nuclear envelope disappears
difference between a chromatid and a chromosome
Chromatid - one strand of a chromosome
Chromosome - the whole structure; it can be made of a single chromatid like in normal cells not undergoing mitosis, or two sister chromatids like before mitosis occurs
How do you count the number of chromosomes?
The number of centromeres
When does cytokinesis occur?
Begins in anaphase and ends in telophase
How does cytokinesis occur in animal cells?
A cleavage furrow forms (due to the action of a contractile ring) which then divides the cell membrane
How does cytokinesis occur in plant cells?
Don’t know if you need to know this
Vesicles containing cell wall building materials line up where the cells intend to separate. Lots of vesicles then join up and expand towards the already-existing parent cell walls to form the new cell wall.
The vesicle membranes fuse to form a plasma membrane that divides the cell into two
zygote
The dilpoid cell formed immediately after fertilisation
homologous chromosomes
A pair of chromosomes of (usually) the same size and with the same genes, but potentially having different alleles - there’s one maternal chromosome and one paternal chromosome
reduction division
A division that halves the number of chromosomes to the normal number (i.e. the first division in meiosis)
equational division
A division which produces genetically identical cells - the total number of chromosomes is kept the same (e.g. the second division in meiosis)
What happens in prophase 1 that is different to prophase in mitosis?
- Homologous chromosomes have been paired up (rather than sister chromatids forming chromosomes)
- Crossing-over of chromatids occurs between the homologous chromosomes (not sister chromatids)
What is produced after the first cytokinesis in meiosis?
Two haploid daughter cells
What is produced after the second cytokinesis in meiosis?
Four haploid daughter cells
What is separated in anaphase 2? What does this form?
Chromosomes are separated into sister chromatids
In meiosis, the parent cell is ____.
diploid
recombination
Another name for crossing over of chromatids between homologous pairs (not sister chromatids)
What two things can a chromosome be?
- A double-armed chromosome (just formed by the cell replicating its DNA in the synthesis stage of interphase)
- A sole chromatid (just separated by mitosis/second division of meiosis)
A chromosome composed of a single chromatid (just separated by mitosis/second division of meiosis) has a centromere. T/F?
True - every chromosome has one centromere.
Describe the role of the centromere in mitosis. [2]
The centromere holds the two sister chromatids together, attaches them to the spindle and divides, allowing the sister chromatids to move to opposite poles of the cell
Explain how meiosis creates genetic variation.
- Crossing over (swapping) of chromatids between the homologous pairs (not sister chromatids) in prophase 1 mean that the chromatids now have a different combination of alleles to each other.
- Independent assortment of chromosomes - the homologous pairs line up randomly at the equator of the cell, so the daughter cells get a mix of maternal and paternal chromosomes
- Random fusion of gametes
two purposes of meiosis
- To ensure the normal number of chromosomes is restored in fertilisation
- To increase genetic variation
Explain a benefit of genetic variation.
It decreases the possibility of unfavourable traits occuring in the offspring (e.g. recessive disorders)
Name the one exception of where homologous chromosomes aren’t always the same size.
X and Y chromosomes
In interphase before meiosis occurs, DNA ____ in homologous pairs.
associates
I think this is right, but don’t quote me
By the end of cytokinesis following telophase 1 of meiosis, each nucleus of the new cells only has ____ of the chromosomes of each homologous pair.
one
Each nucleus has one of the chromatids from the chromosome cell entering prophase 2 so is ____.
haploid
multicellular
An organisms made of many different cell types specialised for their function
erythrocyte
red blood cell
neutrophil
A white blood cell (more specifically, a type of phagocyte)
Give three ways stem cells can be used.
- repairing damaged tissues
- treating conditions of the brain
- researching into developmental biology
How can stem cells be used to treat problems with the brain?
Stem cells can be grown to replace dying brain cells
How can stem cells be used to research into developmental biology?
Stem cells can be observed to better understand how organisms grow, and so how disorders and cancers develop
Describe how stem cells can be used. [3 marks?]
To test the toxicity (1) and efficacy (1) of new drugs
Stem cells can be grown and studied to see how they develop into different cell types (1)
Stem cells can be studied to find out why some cells fail to work properly (e.g. in the brain) (1)
totipotent
A cell that can differentiate to all cell types, including extra-embryonic tissues e.g. placental cells
pluripotent
A cell that can differentiate to all cell types, but this doesn’t include extra-embryonic tissues like placental cells
multipotent
A cell that can differentiate to any cell type within a particular tissue/organ (e.g. the ones in the brain)
nullipotent
A cell that cannot differentiate to any cell type i.e. it has already fully differentiated
Are zygotes pluripotent? True or false and why.
False - they are totipotent so can differentiate into any sort of human cell (this includes adult cells and placental cells).
State how ‘potent’ embryonic stem cells are. Explain your answer.
They are pluripotent as they have already partially differentiated / can’t differentiate into extra-embryonic tissues e.g. the placenta or umbilicus (belly button)
What is meant by a cell’s potency?
The cell’s ability to differentiate; how many cells can the cell differentiate to
tissue
A group of one or more different cell types (plus any extracellular material they secrete) specialised to perform a specific function
vascular cambium
Don’t know if you need to know this.
The main meristem tissue inside plants with stems cells that then differentiate into xylem and phloem vessels
Explain how a sperm cell is shaped to perform its function.
Head/cap/acrosome is shaped to allow the sperm cell to penetrate the egg.
1 neutrophil adaptation linked to function/s
This flashcard is dedicated to the hardest to remember adaptation for this organelle for me, not all the different possibilities
Flexible shape
-> can engulf foreign particles or pathogens (main)
-> can squeeze through cell junctions (between cell membranes) in the capillary wall
1 erythrocyte adaptation linked to function
This flashcard is dedicated to the hardest to remember adaptation for this organelle for me, not all the different possibilities
Flexible shape
-> can squeeze through narrow capillaries
An erythrocyte has typical efficient exchange surface adaptations. Therefore what are some of its adaptations?
- Large surface area to volume ratio
- Short diffusion distance for oxygen to reach all the haemoglobin
What can epithelial cells have on them?
- Cilia (ciliated epithelium)
- Microvilli
ciliated epithelium
tissue made of ciliated cells
epithelial cell adaptation (linked to function)
Non-specific to the types of epithelial cells so I don’t think you need to know this - just know its structure
epithelial cells share a membrane base
-> supports the overlying epithelium by anchoring it onto the connective tissue
ciliated epithelium tissue adaptation (linked to function)
Have cilia
-> these beat in a coordinated rhythm to move material along its surface
2 epithelium tissue in the small intestine adaptations (linked to function)
Have microvilli - these are folds in the cell membrane
-> increases surface area
1 palisade cell adapation linked to function
This flashcard is dedicated to the hardest to remember adaptation for this organelle for me, not all the different possibilities
Thin cell wall
-> short diffusion pathway for CO2 and O2 to diffuse across
2 squamous epithelium adaptations (linked to function)
One (thin) layer of flattened cells that fit together tightly
-> efficient gas exchange
Permeable
-> easy exchange of gases
Give 2 places where you would find squamous epithelium.
Alveoli lining and blood vessels
Give 2 places where you would find ciliated epithelium. Describe how they are connected,
Respiratory ststem (e.g. trachea, bronchi) and oviducts
(any surface where something needs to be moved)
1 root hair cell adapation linked to function
This flashcard is dedicated to the hardest to remember adaptation for this organelle for me, not all the different possibilities
Thin, permeable cell wall
-> short diffusion pathway for water and ions to travel across
1 guard cell adapation linked to function
thin outer cell wall and thick inner cell wall
-> force guard cell to bend outwards to open the stoma (pore)
three types of muscle cells
Cardiac, skeletal and smooth (normal muscles)
1 muscle cell adapation linked to function
layers of protein filaments
-> layers can slide over each other, causing muscle contraction
Where might you find muscle tissue (3)?
Stomach
Skeleton (between bones)
Heart
cartilage structure
Where might you find cartilage (3)?
Nose & ears
Trachea (tracheal rings)
Joints (a type of connective tissue found within)
2 cartilage functions
To provide support
To stop bones from rubbing against each other in the joints
How is cartilage formed?
Chondroplast cells secrete a matrix (jelly-like substance with protein fibres) which they get trapped inside
Xylem tissue only contains dead cells. True or false? Explain your answer.
False - xylem tissue also contains living parenchyma cells which fill in gaps between the xylem vessels
What is phloem tissue made of?
Sieve cells, companion cells and normal cells
What is a sieve cell?
A phloem vessel cell with end walls (sieve plates) at each end - these have pores/perforations for cell sap to travel through)
What do companion cells do?
They help sieve cells with living functions and metabolism e.g. they have lots of chloroplasts for respiration - lots of energy is required for the active transport of substances
Why do you press down on the cover slip when investigating cells undergoing mitosis?
To get a single layer of cells which allows light to pass through them (to be seen through the microscope)
When counting cells to calculate the mitotic index, what should you do to ensure your count is accurate?
- Examine a large field of view / many cells
- Ensure you have a representative sample
somatic cells
Cells in the body other than sperm and egg cells (i.e. non-gametes)
ploidy
The number of chromosomes an organism usually has e.g. 46 for humans
Bone marrow contains stem cells that can develop into e.g. erythrocytes. One change that occurs is that they remove their nucleus. Describe t=another change that must occur inside these stem cells as they differentiate to form erythrocytes.
They synthesise haemoglobin
Suggest three ways in which the use of embryonic stem cells in research has practical benefits to biological knowledge. [3]
- To test drug efficacy
- To test drug toxicity
- To research how cells fail in different diseases
- To study how cells develop into different cell types / cell differentiation
What is the name for the point at which the chromosomes contact in crossing over?
chiasma (chiasmata pl.)
Explain why, when Harry was investigating the stages of mitosis in a garlic root, he firmly squashed the root tip. [1]
To ensure a thin, flat layer of cells so that light can travel through
Romeo was investigating the stages of mitosis in garlic root tips, counting the number of cells in each stage of the cell cycle.
A different set of results was obtained when the count was repeated a few days later, after having been rejected by Rosaline. Give two reasons for the difference in results. [2]
The root tips may be of different ages
Different temperature
Different water availability
Different type of garlic was used
Different time of day
Different nutrient availability
Compare DNA replication and transcription. [6]
Similarities:
* Both use helicase (1) to unzip the DNA molecule (1)
* Both use a DNA strand as a template strand
* Both have hydrogen bonding (1) between the complementary base pairs (1)
* Both form a new strand using free, activated nucleotides
Differences:
* Different helicases
* Different polymerases
* DNA replication uses DNA nucleotides whereas transcription uses RNA nucleotides
* DNA replication produces two DNA double helices, whereas transcription produces one mRNA strand
* Only a small section of DNA is used in transcription, whereas the whole thing is used in DNA replication
* mRNA leaves the nucleus in transcption whereas the DNA strands produced in DNA replication don’t leave the nucleus
activated nucleotide
Essentially one that can react to join other activated nucleotides e.g. for
DNA replication or transcription
