6- Cell divisions Flashcards
(143 cards)
1
Q
What are the two types of cell division
A
Mitosis
Meiosis
2
Q
What is the cell cycle?
A
high ordered regulated sequence of events that take place in a cell
3
Q
What are the 3 phases of the cell cycle?
A
Interphase
Mitosis
Cytokenesis
4
Q
What phases do cells spend the majority of there time in?
A
Interphase
5
Q
What happens during interphase?
A
- DNA is replicated
-Protein synthesis occurs in the cytoplasm
-Cell grows
6
Q
What are the three stages of interphase?
A
G1
S
G2
7
Q
What happens during G1 phase?
A
-cell elongates, grows in size
-organelles replicate
-proteins made
8
Q
What happens during the S phase?
A
-DNA is replicated in the nucleus
9
Q
What happens during the G2 phase?
A
-cell continues to grow in size
-energy stores are increased
-proteins made
-replicated DNA is checked for errors
10
Q
What happens after the cell completes the cell cycle?
A
process either starts again or exits the cycle
11
Q
What is G0?
A
-when the cell leaves the cycle
-temporarily or permenately
12
Q
What do cells leave the cycle?
A
when a cell is specialised to perform a specific function - no longer able to divide
DNA of a cell is damaged - no longer viable, enters a period of permanent cell arrest
Age - as you age the umber of cells in your body increase. Growing number of senescent cells = age related diseases eg. arthritis, cancer
Some can be stimulated to return - lymphocytes in an immune response
13
Q
What are checkpoints in the cell cycle?
A
Control mechanisms which monitor and verify whether processes of each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase
14
Q
What are the checkpoints called throughout the cell cycle?
A
G1
G2
Metaphase
15
Q
What is the G1 checkpoint?
A
At the end of the G1 phase before entry to S phase
Checks for cell size, nutrients, growth factors and DNA damage
16
Q
What is the G2 checkpoint?
A
At end of G2 before the start of mitotic phase
Checks for cell size, DNA damage, DNA replication
17
Q
What is the metaphase checkpoint?
A
At the spindle attatchement stage
Checks for chromosome spindle attachment
18
Q
What is the mitosis stage?
A
The division of the genetic material in a cell.
19
Q
What is cytokinesis?
A
The final stage. The cytoplasm divides and two genetically identical cells are formed
20
Q
What is the significance of mitosis?
A
-growth, replacement and repair of tissues
-asexual reproduction in plants, fungi and some animals
21
Q
What must happen before mitosis can occur?
A
DNA in nucleus is replicated
22
Q
What happens when a chromosome is replicated during S phase?
A
It consists of two copies of the double helix. Each copy is called a chromatid and they are joined in the middle by a centromere
23
Q
Why are the chromosomes not visible in interphase?
A
DNA is uncondensed
24
Q
What are the 4 stages of mitosis?
A
Prophase
Metaphase
Anaphase
Telophase
25
What happens during prophase?
- the chromosomes condense and become visible
-nucleolus disapears
-nuclear envelope begins to break down
-centrioles move to poles of cell and begin to produce spindle fibres
26
What happens during metaphase?
-nuclear membrane has disappeared
-spindle fibres have attactched to the centromere of chromosomes
-chromosomes are pulled to the middle/equator of cell where they line up
27
What happens during anaphase?
-spindle fibres contract and centromere of each chromosome spilts
-one chromatid from each chromosome is pulled to opposite poles of the cell
28
What happen during telophase?
-nuclear envelope begins to reform around each group of chromosomes
-spidnle fibres disappear
-chromosomes begin to uncoil and become less distinct
29
What happens during cytokenesis?
Cytoplasm begins to divide to from two new genetically identical daughter cells. Each cell will now have a full copy of the genetic material
30
What is the mitotic index?
How much mitosis is happening in a tissue
31
How do you calculate mitotic index?
number of cells in mitosis / total number of cells
32
Why is a toluidine blue stain used when observing mitosis?
it binds to the chromosomal DNA staining it deep blue to make chromosomes visible
33
Why is acid used when observing mitosis?
Helps to break down the cell walls and make them more permeable to allow stain to penetrate the cell and reach chromosomes
34
What is the method for observing mitosis?
1. Remove the water from the test tube containing garlic and replace in with warm HCL
2. Leave the test tube containing garlic clove and acid in a water bath at 40 degrees for 5-10 minutes
3. Use a cocktail stick to remove garlic clove and gently rinse the roots in water to remove acid
4. Cut of the terminal 3mm of the root tips and allow to fall onto a small watch glass
5. Add one drop go 1% toluidine blue stain and leave the roots to stain
6. Remove the excess stain and rinse the root tips using a pipette and distilled water
7. Use a mounted needle to carefully transfer the root tips to a clear microscope slide
8. Add a drop of water to the root tips and gentry spread them out so there not overlapping
9. Carefully place coverslip on top minimising production of air bubbles
10. Cover the slide and cover slip with a paper towel
11. Avoiding sideways movement, gently press down on the coverslip with a thumb to squash the root tips and spread them out
12. View the root tip squash through a light microscope with the X10 then the X40 objective. Look over the whole prepared slide.
35
Hoe many chromosomes are in the genetic material of humans?
-46 chromosomes
-23 from mother, 23 from father
36
How many pairs of chromosomes does a normal human have?
23
37
What does a gene do?
code for a characteristic
38
How many chromatids is a chromosome made up of?
-1 or 2
-2 are genetically identical
39
What is a chromatid?
a strand of DNA
40
What is a centromere?
the point on a chromosome which holds together 2 chromatids and spindle fibres can attach
41
What happens to homologous chromosomes before cell divison?
they are copied
42
What is bivalent?
where pairs of homologous chromosomes attach to each other at points called chaisma (singular) or chaismata (plural)
43
What occurs during Prophase 1 of meiosis?
-chromosomes condense
-nuclear envelope disintegrates
-homologous chromosomes pair up to form bivalents (CROSSING OVER)
-centrioles migrate to poles of cell
-spindle fibres begin to form
44
What is independant assortment?
where homologous chromosomes line up with random alignments along the metaphase plate during metaphase in meiosis
45
What occurs during Metaphase 1 during meiosis?
-homologous pairs assemble along metaphase plate with random orientations
-spindle fibres from each centriole attach to centromeres
46
What occurs during Anaphase 1 during meiosis?
-homologous chromosomes pulled to opposite poles of the cell by spindle fibres, sister chromatids stay attached
-sections of DNA entangled during crossing over breaks off and rejoin, sometimes resulting in exchange of DNA
-points at which they break + rejoin are called chiasmata
-genetic variation arises, sister chromatids no longer identical
47
What is a recombinant chromatid?
one with a different genetic makeup to either the father or the mothers chromatid due to sections of DNA entangled during crossing over being exchanged
48
What occurs during Telophase 1 during meiosis?
-chromosomes assemble at the pole of each cell and uncoil
-Nuclear envelope reforms
-Centrioles move back to cytosol
-Cell surface membrane, invaginates and pinches off into two daughter cells, each with the same amount of genetic information from each parent
-Reduction of chromosomes from diploid to haploid
49
what occurs during Prophase 2 during meiosis?
-chromosomes condense and become visible again
-Nuclear envelope disintegrates
-Centrioles migrate to poles of the cell, spindle fibres begin to form
50
what occurs during Metaphase 2 in meiosis?
-individual chromosomes lineup, along metaphase plate again with independent assortment
-Spindle fibres attach to centromeres
-Due to crossing over, the chromatids are no longer identical so there is more genetic variation
51
what occurs during Anaphase 2 in meiosis?
-chromatids of individual chromosomes are pulled to poles of cell by shortening of spindle fibres after the division of centromeres
52
what occurs during Telophase 2 in meiosis?
-Chromosomes assemble at poles then uncoil and form chromatin again
-nuclear envelope reforms
-each cells surface membrane invaginates and pinches off to form two new daughter cells, each with half the genetic information of the original parent cell
53
What is a diploid number of chromosomes?
the full number of chromosomes in a normal cell (46-humans)
54
What is a haploid number of chromosomes?
half the normal amount of chromosomes (23 - humans)
55
What is a spore?
a cell which is adapted for survival and dispersed in unfavourable conditions
56
How does meiosis ensure variation within a species?
1. crossing over between homologous chromosomes
2. fertilisations (1/2 of the genetic info from mother and father)
3. independent assortment and segregation of both homologous and non-identical sister chromatids
57
What is a specialised cell?
a cell which has adaptations which help it carry out a specific function
58
What is a tissue?
a group of the same specialised cells, which work together to carry out a function
59
What is another name for an erythrocyte?
a red blood cell
60
What shapes do erythrocytes have and why?
a flattened biconcave shape to increase their surface area and SA:V ratio
61
What are the 3 adaptations which erythrocytes have in order to help them transport oxygen around the body?
1. flattened biconcave disc
2. flexible, fit through narrow capillaries
3. in mammals they lack nuclei to leave more space for haemoglobin
62
What is the function of a sperm cell?
to deliver genetic information to the female gamete, the ovum
63
What adaptation do a sperm cell have?
1. a flagellum containing microtubles and many mitochondria giving them the ability and energy to swim
2. an acrosome on its head containing digestive enzymes, which are released to digest the protective layers around the ovum and allow the sperm to penetrate
3. protein fibres to strengthen the tail
64
What type of nucleus does a sperm cell have?
haploid nucleus
65
What adaptation does a palisade mesophyll have?
-many chloroplasts to absorb lots of light for photosynthesis
-shape of cell is rectangular, so can be closely packed to form continuous layer
-thin cell walls, increasing the rate of CO2 diffusion
-large vacuole to maintain turgor pressure
66
What is a neutrophil a type of?
white blood cell
67
Why do neutrophils have a multi-lobed nucleus?
to make it easier for them to squeeze through small gaps to get to the site of infections
68
What adaptations does a neutrophil have?
-multi lobed nucleus so if is easy to squeeze through small gaps to get to the sight of infection
-granular cytoplasm containing many lysosomes used to attack pathogens
69
What is the function of palisade mesophyll cells?
take in light via chlorophyll for photosynthesis
70
What is the function of a neutrophil?
plays an important role in the immune system
71
What is the function of root hair cells?
uptakes water and minerals from soil
72
Where are root hair cells found?
surface of the roots near the growing tips
73
What adaptation does a root hair cell have?
-long,thin extension to maximise SA:V ratio
-vacuole containing cell sap to lower water potential and maximise concentration gradient or take up water by osmosis
74
What is the function of a pair of guard cells?
to open and close one stomata
75
What happens once a guard cell loses water?
it becomes less swollen and changes shape, closing the stomata to prevent further water lossc
76
Why does a guard cell not change symmetrically?
because the cell wall is thicker on the inside and thinner on the outside
77
What is the hole between 2 guard cells called?
stomata aperture
78
What are the four main categories of tissues in animals?
-nervous tissue (adaptation to support transmission of electrical impulses)
-epithelial tissues (adapted to cover body surfaces)
-muscle tissue (adapted to contract)
-connective tissue (adapted to either hold other tissues together or as a transport medium)
79
What is the average lifespan of a human neutrophil?
6 houra
80
What is the structure of squamous epithelial tissue?
a single layer of squamous cells attached to a basement membrane
81
How is squamous epithelial tissue adapted to aid diffusion?
very thin due to being only one cell thick
82
What is the structure of ciliated epithelial tissue?
-ciliated epithelial cells (with cilia) mixed with goblet cells, all on a basement membrane
83
What are the 3 types of cartilage?
1. Hyaline (rubbery, but still somewhat though- found between bones and joints)
2. Elastic - lots of elastin so very flexible eg. outer ears
3. Fibrocartilage - densely packed with collagen so very tough and resistant to shock and compression, found in intervertebral discs
84
What type of tissue is cartilage?
connective
85
What two protein fibres does cartilage contain?
elastin and collagen
86
What is the structure of cartilage?
chondrocyte cells embedded in a extracellular matrix
87
What are two types of muscle fibres?
skeletal and cardiac
88
What is special about cardiac muscle fibres?
they can contract without stimulation from the nerves, instead basing their rhythm on pacemaker cells
89
Why does muscle need to be able to contract?
In order to move bones, which in turn move the parts of the body
90
What do skeletal muscles contain?
myofibrils, which contain contractile proteins
91
How are cells connected in muscle fibres?
by collagen - when the cells contract, it pulls on the collagen, causing tension which can cause movement
92
What organelles do muscle cells have more of?
Mitochondria and ribosomes (to pride actin and myosin fibres)
93
What are the two broad types of tissue in plants?
1. epidermis tissue (adapted to cover plant surfaces)
2. vascular tissue (adapted for transport of water and nutrients)
94
What are 3 specific specialised plant tissues?
xylem
phloem
epidermal
95
What is the structure and function of epidermis tissue?
-single layer of closely packed cells covering the surface of plants
-usually covered by a waxy, waterproof tissue to reduce water loss
-stomata and guard cell present, allow CO2 in and out, water vapour and oxygen in and out
96
What are the xylem cells, its structure and function?
-type of vascular tissue
-responsible for transport of water and minerals through plants
-tissue is composed of vessel elements, which are elongated dead cells
-walls of cells are strengthened with a waterproof material called lignin which provides structural support for plants
97
What are the phloem cells, its structure and function?
-type of vascular tissue
-responsible for the transport of organic nutrients (particularly sucrose from leaves and stems where it is made by photosynthesis to all parts of the plant where it is needed)
-composed of columns of sieve tube cells separated by perforated walls called sieve plates
98
What are examples of organ systems in animals?
1. Digestive system - takes in food, breakers down the large insoluble molecules, absorbs the nutrients in blood, retains water needed by the body and removes any undigested material
2. Cardiovascular system - moves blood around the body to provide an effective transport system for the substances it carries
3. Gaseous Exchange System - brings in air to the body so O2 can be extracted for respiration, and CO2 can be expelled
99
What is an organ system?
a number of organs working together to carry out a major function in the body
100
What is differentiation?
the process of a cell becoming specialised
101
What are stem cells?
undifferentiated cells which re genetically identical and have the ability to develop into any of the various types of cell
102
what are the two key features of stem cells?
-retain the ability to divide repeatedly (SLEF RENEW)
-differentiate (become specialised)
103
What is potency?
a stem cells ability to differentiate into different cell types
104
What are totipotent stem cells?
-cells that differentiate into embryonic and extra-embryonic tissues
-they form the embryo and the placenta
-all genes in the nucleus can be activated
-designed eventually to produce a whole organism
105
What are pluripotent stem cells?
-cells that can differentiate into any embryonic cell type
-occur in early embryos of mammals, cambium and plants
-most genes are still available to be be activated
106
What are multipotent stem cells?
-they can divide to form different cell types but not all
-eg. stem cells in bone marrow that form most cells of the immune system
-a large number of genes have been switched off
107
What are unipotent stem cells?
-cells that can only form one type of cell
-eg. cardiomyocytes can divide to form heart muscle cells
-lots of genes have been switched off via regulation of transcription factors
108
What are embryonic stem cells?
-taken from the embryo
-after about 7 days a mass of cells (blastocyst) has formed, cells now in pluripotent stage
-due to their potency embryonic stem cells can be used to grown new organs and tissues for treatment variety of conditions eg. parkinson’s, alzheimer’s
-could save and improve quality of life’s
109
What are objections to the use of embryonic stem cells in medicine?
1. unused IVF embryos - can be donated to research instead of destroyed. Some people object to this as it is the destruction of a potential foetus, fertilisation that has happened has the right to life
2. egg cells frozen for IVF which have not been fertilised can be stimulated to divide - less objection as they would not survive after a few days if implanted into a uterus would not create a foetus
110
What are adult stem cells?
-can be obtained form the body tissues of an adult
-found in specific areas such as bone marrow
-mutlipotent so cannot differentiate into as many types of cells as embryonic stem cells
-bone marrow transplants have been successful to replace fault bone marrow that produces abnormal blood cells eg. lukemia, sickle-cell anemia
111
What are induced pluripotent stem cells used for?
-created in a lab from specialised adult cells after ‘reprogramming’ them to become pluripotent
-cells made to express number of transcription factors
-they switch on genes that are normally expressed in cells that have pluripotency
-could allow adult cells to become as plastic as embryonic stem cells without the same ethical issues
-they could be made out of patients own stem cells = no rejection
112
What are the sources of plant stem cells?
-stem cells present in meristem tissue
-tissue is found where growth is occurring in plants eg. roots and shoots
-tissue is also found sandwiched between the phloem and xylem tissues, this meristem is called vascular cambium
-pluripotent nature of stem cells in the meristems continues throughout the life of the plant
113
What are the uses of stem cells?
1. heart diseases - muscle tissue is heart is damaged as a result of heart attack , normally not fixable
2. type 1 diabetes
3. Parkinson’s disease - symptoms caused by death of dopamine-producing cells in the brain
4. Alzheimer’s- brain cells are destroyed as result of build up of abnormal proteins
5. Macular degeneration- blindness in the elderly + diabetics
6. Birth defects
7. Spinal cord injuries
114
What diverse areas are stem cells already being used in?
1. Treatment of burns - stem cells grown on biodegradable meshes can produce new skin for burn patient
2. Drug trials - potential new drugs can be tested on cultures of stem cells being tested on animals and humans
3. Development biology - with their ability to divide indefinitely and differentiate into almost any cell, stem cells have become an important area of study
115
What can totipotent stem cells produce apart from cells from the embryo?
cells for the amnion (amniotic sac) or umbilicus (umbilical cord)
116
What are undifferentiated cells called?
stem cells
117
why does the replication of stem cells have to be tightly controlled?
if they do not divide quickly enough then tissues will be replaced inefficiently, leading to aging, but there is uncontrolled division then they can form tumours
118
What can be created from pluripotent stem cells?
any type of tissues, but not new organisms
119
How can scientists produce pluripotent stem cells?
by genetically manipulating cells found in the umbilical cords and some parts of adults (these would be mutlipotent before manipulation)
120
Where are the stem cells which create all blood cells located?
bone marrow
121
What can be crested from multipotent stem cells?
a few types of cells, such as erythrocytes
122
What is the name for the type of stem cell which blood cells are created from?
haematopoetic stem cells
123
What are the new cells created from stem cells necessary for?
growth, development and tissue repair
124
What is the name for the ability of a stem cell to differentiate?
potency
125
What is the average lifespan of a human erythrocyte?
120 days
126
What are the 3 steps that occur for a haematopoetic stem cell to be converted to an erythrocyte?
1. nucleus and organelles lost
2. haemoglobin made
3. cell shape changed
127
What are the 3 steps that occur for a haematopoetic stem cell to be converted to a neutrophil?
1. more lysosomes created
2. nucleus becomes multi-lobed
3. extensive cytoskeleton created
128
When are more neutrophils produced from stem cells?
during infection
129
What are the two broad sources of human stem cells?
adult, embryonic
130
What are some advantages of taking stem cells from the umbilical cord?
No invasive surgery, plentiful supply of umbilical cords, cells could be stored if owner of umbilicus ever needed them with no risk of rejection
131
Where are stem cells found in plants?
Meristems, which are found in the cambium between the xylem and phloem, as well as tips of roots/shoots or anywhere else growth is occurring
132
What are the 4 steps that occur for a plant stem cell to be converted into a xylem cell?
1. loss of cytoplasm + contents
2. lignin deposited
3. elongation of cells
4. end walls lost
133
What are the 2 steps for a plant stem cell to be converted into a phloem cell?
1. some loss of cytoplasm and organelles
2.sieve plate development
134
What potency of stem cells are plant stem cells all through the plants adult life?
pluripotent
135
How have stem cells been used in medicine for years already?
in form of bone marrow transplants
136
What causes the most ethical issues with the use of embryonic stem cells?
The fact that extracting stem cells from embryos usually involves destroying the embryo
137
What are some ethical objections to/issues with the use of embryonic stem cells?
1. religious objections
2. moral objections ie. life begins at conception, therefore harvesting embryo classed as murder
3. lack of consensus on who holds genetic material taken from embryos
138
Why is using embryonic stem cells better and worse than using umbilical stem cells?
Embryonic stem cells are pluripotent, can divide into more things then multipotent umbilical cords, but use of umbilical stem cells removes any ethical issues
139
What are some disadvantages of using adult stem cells instead of umbilical stem cells?
They do not divide as well
are more likely to have acquired mutations
140
What is an organ?
a collection of tissues which are adapted to preform a function
141
Describe how new xylem cells are produced?
-produced in the meristem/cambium
-by differentiation from stem cells
142
Where are all blood cells derived from?
stem cells in the bone marrow
143
What is the end product of meiosis?
4 genetically different haploid cells
