The Cell Cycle Flashcards
1
Q
What is the cell cycle?
A
The cell cycle is the process that all body cells in multicellular organisms use to grow and divide.
2
Q
What is step 1 of the cell cycle?
A
1) The cell cycle starts when a cell has been
produced by cell division and ends with the
cell dividing to produce two identical cells.
3
Q
What is step 2 of the cell cycle?
A
2) The cell cycle consists of a period of cell
growth and DNA replication, called
interphase, and a period of cell division,
called M phase. M phase involves mitosis
(nuclear division) and cytokinesis
(cytoplasmic division).
4
Q
What is step 3 of the cell cycle?
A
3) Interphase (cell growth) is subdivided
into three separate growth stages.
These are called G1 , S and G2
5
Q
What is step 4 of the cell cycle?
A
4) The cell cycle is regulated by checkpoints.
Checkpoints occur at key points during the
cycle to make sure it’s OK for the process
to continue.
6
Q
What is the g1 phase
A
G1 checkpoint The cell checks that the chemicals needed for replication are present and for any damage to the DNA before entering S-phase.
7
Q
What’s S phase
A
Synthesis phase
SYNTHESIS
cell replicates its DNA, ready to divide by mitosis
DNA replication
Each chromosome becomes two identical copies (chromatids)
8
Q
Whats the G2 phase
A
Second growth phase
G2 Checkpoint
The cell checks whether all the DNA has been replicated
without any damage. If it has,the cell can enter mitosis.
Growth of the cell
stores are increased
Duplicates DNA is checker for errors
9
Q
Why do cells leave the cell cycle 1 differentiation
A
When a cell becomes specialised to carry a particular function it will leave the cell cycle
10
Q
Why do cells leave the cell cycle 2
A
DNA may be damaged
11
Q
Why do cells leave the cell cycle 3
A
Cells only dived a limited number of times then become senescent with age the number of these cells in the body increases
12
Q
Why is mitosis important?
A
Tissue growth
Tissue repair replacement of damaged or worn out cells
Asexual reproduction
13
Q
What’s asexual reproduction
A
Genetically identical offspring from one parent in multicellular organisms
14
Q
What are chromosomes converted to in DNA replication
A
Genetically identical DNA molecules known as chromatids
15
Q
As mitosis begins, the chromosomes are made of two strands joined in the middle by a?
The separate strands are called?
A
As mitosis begins, the chromosomes are made of two strands joined in the middle by a centromere. The separate strands are called chromatids.
16
Q
Why are there two strands?
A
There are two strands because each chromosome has already made an identical copy of itself during interphase. When mitosis is over, the chromatids end up as one-strand chromosomes in the new daughter cells.
17
Q
Where do spindle fibres attach to move chromatids around the cell
A
Centromere
18
Q
What’s mitosis divided into
A
Prophase
Metaphase
Anaphase
Telophase
19
Q
What is IPMAT
A
Interphase Prophase Metaphase Anaphase Telophase
20
Q
Whats interphase?
A
Interphase comes before mitosis in the cell cycle. It’s when cells grow and replicate their DNA ready for division.-Interphase —
The cell carries out normal functions,
but also prepares to divide. The cell’s DNA is
unravelled and replicated, to double its genetic
content. The organelles are also replicated so it
has spare ones, and its ATP content is increased
(ATP provides the energy needed for cell division).
21
Q
What’s prophase
A
Prophase — The chromosomes condense, getting shorter and fatter. Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. The nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm.
22
Q
What’s metaphase
A
Metaphase — The chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere. At the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue.
23
Q
What is anaphase
A
3) Anaphase — The centromeres divide,
separating each pair of sister chromatids.
The spindles contract, pulling chromatids
to opposite ends of the cell, centromere first.
24
Q
What is telophase
A
4) Telophase — The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again. They’re now called chromosomes again. A nuclear envelope forms around each group of chromosomes, so there are now two nuclei.
25
Cytokinesis definition
```
Cytokinesis — The cytoplasm divides.
In animal cells, a cleavage furrow
forms to divide the cell membrane.
There are now two daughter cells
that are genetically identical to the
original cell and to each other.
Cytokinesis usually begins in
anaphase and ends in telophase.
It’s a separate process to mitosis.
```
26
Cytokinesis In animal cells
Cleavage furrow forms around the middle of the cell. The cell surface membrane is pulled inwards by the cytoskeleton until it’s close enough to fuse around the middle forming two cells.
27
Cytokinesis in plant cells.
Plants have a cell wall so it’s not possible for a cleavage furrow to form. Vesicles from the Golgi apparatus begin to assemble in the same place as where the metaphase plate was formed the vesicles fuse with each other dividing the cell into two
28
How to observe the cell cycle and mitosis by staining chromosomes?
You can stain chromosomes so you can see
them under a microscope. This means you can
watch what happens to them during mitosis —
and it makes high-adrenaline viewing, I can tell
you. These are some plant root cells shown
under a light microscope at different stages of
the cell cycle and mitosis. You need to be able
to recognise, draw and label each stage.
29
What happens in sexual reproduction?
1) In sexual reproduction two gametes (an egg and a sperm) join together at fertilisation to form
a zygote. The zygote then divides and develops into a new organism.
30
What is meiosis?
What does it involve?
Cells formed by meiosis are all genetically different because?
2) Meiosis is a type of cell division that happens in the reproductive organs to produce gametes.
3) Meiosis involves a reduction division. Cells that divide by meiosis have the full number of
chromosomes to start with, but the cells that are formed from meiosis have half the number.
Cells with half the normal number of chromosomes are called haploid cells.
4) Cells formed by meiosis are all genetically different because each
new cell ends up with a different combination of chromosomes.
31
How many gametes does meiosis produce.
Meiosis produces 4 gametes, each is haploid and are all genetically
different
32
At fertilisation fusion of two Gametes produce what
Diploid cells
33
How many divisions does meiosis have?
2
34
What are the 2 divisions?
Whats meiosis split up into?
What does the process begin by?
What happens to the DNA?
1) Meiosis involves two divisions: meiosis I and meiosis II.
Meiosis I is the reduction division (it halves the chromosome number).
2) Like mitosis meiosis I and meiosis II are each
split into prophase, metaphase, anaphase and telophase stages.
The whole of meiosis begins with interphase. During interphase, the DNA unravels and replicates to produce double-armed chromosomes called sister chromatid
35
Meiosis overview
1. Meiosis involves two divisions of the cell & nucleus
2. Homologous chromosomes pair up during 1s division (pairs are
called bivalents) and swap portions of chromatids (crossing-over)
3. Homologous chromosomes separate during the 1st division.
4. Chromatids separate during the 2nd division.
5. One diploid parent cell forms four haploid gametes (sex cells with
half the chromosome number).
6. Gametes are all genetically different.
36
What is interphase 1
```
POINT MUTATION (BEFORE MEIOSIS)
During interphase, the DNA unravels and replicates to produce double-armed chromosomes called sister chromatid
```
37
What’s prophase 1ST division?
Prophase I
The chromosomes condense, getting shorter and
fatter. The chromosomes then arrange themselves into
homologous pairs (see yellow box) and crossing-over
occurs (see next page). Just like in mitosis, centrioles
start moving to opposite ends of the cell, forming the
spindle fibres. The nuclear envelope breaks down.
38
What’s metaphase 1st division
```
Metaphase I
The homologous pairs line
up across the centre of the
cell and attach to the spindle
fibres by their centromeres.
```
39
What’s anaphase 1st division
Anaphase I
The spindles contract, separating the homologous
pairs — one chromosome goes to each end of the cell.
40
What is telophase 1st division?
Telophase I
A nuclear envelope forms
around each group of
chromosomes.
41
Cytokinisis?
Cytokinesis (division of the
cytoplasm) occurs and two
haploid daughter cells are produced.
42
What are homologous pairs?
A Note About Homologous Pairs:
Humans have 46 chromosomes in total — 23 pairs.
One chromosome in each pair came from mum and
one from dad, e.g. there are two number 1’s (one from
mum and one from dad), two number 2’s etc. The
chromosomes that make up each pair are the same size
and have the same genes, although they could have
different versions of those genes (called alleles). These
pairs of chromosomes are called homologous pairs.
43
What happens in the 2nd division?
Meiosis II (second division)
The two daughter cells undergo prophase II, metaphase II, anaphase II, telophase II and cytokinesis — which are a lot like the
stages in mitosis. In anaphase II, the pairs of sister chromatids are separated — each new daughter cell inherits one chromatid from each chromosome. Four (genetically different) haploid daughter cells are produced — these are the gametes
44
What happens when chromatids cross over in prophase 1?
During prophase I of meiosis I, homologous pairs of
chromosomes come together and pair up. The chromatids
twist around each other and bits of chromatids swap over.
The chromatids still contain the same genes but now have
a different combination of alleles.
45
What two Main Events during meiosis leads to genetic variation?
1 Crossing over of chromatids
| 2 Independent assortment of chromosomes
46
what does Crossing over of chromatids mean?
1 Crossing over of chromatids
The crossing over of chromatids in meiosis I means
that each of the four daughter cells formed from
meiosis contains chromatids with different alleles:
47
What happens in independent assortment?
2 Independent assortment of chromosomes
1) Each homologous pair of chromosomes in your cells is made up of one chromosome from your mum (maternal) and one chromosome from your dad (paternal).
2) When the homologous pairs line up in metaphase I and are separated in anaphase I, it’s completely random which chromosome from each pair ends up in which daughter cell.
3) So the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.
4) This is called independent assortment (separation) of the chromosomes.
5) This ‘shuffling’ of chromosomes leads to genetic
variation in any potential offspring.
48
What are stem cells?
specialized cells
49
What are stem cells?
1) Multicellular organisms are made up from many different cell types that are specialised for their function, e.g. liver cells, muscle cells, white blood cells.
2) All these specialised cell types originally came from stem cells.
3) Stem cells are unspecialised cells — they can develop into different types of cell.
4) All multicellular organisms have some form of stem cell.
5) In humans, stem cells are found in early embryos and in a few places in adults. Stem cells in early embryos
can develop into any type of human cell. Stem cells in adults can only develop into a limited range of cells.
50
What does stem cells differentiate into?
specialised cells
51
what is a differentiation?
2) The process by which a cell becomes specialised for its job is called differentiation.
52
In Animals what are adult stem cells used for?
3) In animals, adult stem cells are used to replace damaged cells, e.g. to make new skin or blood cells (see below).
53
Why do plants need stem cells?
4) Plants are always growing, so stem cells are needed to make new shoots and roots throughout their lives.
Stem cells in plants can differentiate into various plant tissues including xylem and phloem (see below).
5) Stem cells are also able to divide to produce more undifferentiated stem cells, i.e. they can renew themselves
54
How do Cells in the Bone Marrow Differentiate into Blood Cells
Cells in the Bone Marrow Differentiate into Blood Cells
Neutrophil (white blood cell)
1) Bones are living organs, containing nerves and blood vessels.
2) The main bones of the body have marrow in the centres.
3) Here, adult stem cells divide and differentiate to replace
worn out blood cells — erythrocytes (red blood cells) and
neutrophils (white blood cells that help to fight infection).
55
How do Cells in the Meristems Differentiate into Xylem and Phloem
Cells in the Meristems Differentiate into Xylem and Phloem
1) In plants, stem cells are found in the meristems
(parts of the plant where growth can take place).
2) In the root and stem, stem cells of the vascular cambium
divide and differentiate to become xylem vessels and
phloem sieve tubes.
56
How might Stem cells cure diseases like Parkinson's?
1) Stem cells can develop into different specialised cell types, so scientists think they could be used to replace
damaged tissues in a range of diseases. For example, it might be possible to use stem cells to treat neurological
disorders like Alzheimer’s and Parkinson’s:
With Alzheimer’s, nerve cells in the brain
die in increasing numbers. This results
in severe memory loss. Researchers are
hoping to use stem cells to regrow healthy
nerve cells in people with Alzheimer’s.
Patients with Parkinson’s suffer from tremors that
they can’t control. The disease causes the loss of a
particular type of nerve cell found in the brain. These
cells release a chemical called dopamine, which is
needed to control movement. Transplanted stem cells
may help to regenerate the dopamine-producing cells.
2) Stem cells are also used by scientists researching developmental biology, i.e. how organisms grow and develop.
Studying stem cells can help us to understand more about things like developmental disorders and cancer.
57
What are examples of specialised animal cells?
Neutrophills
Erythrocytes
epithelial cells
sperm cells
58
What are examples of specialised plant cells?
Palisade mesophyll cells
root hair cells
guard cells
59
How are neutrophils specialized?
1) Neutrophils (a type of white blood cell) defend the body against disease. Their flexible shape allows them to engulf foreign particles or pathogens The many lysosomes in their cytoplasm
contain to the engulfed particles.
60
How are Erythrocytes specialized?
2) Erythrocytes (red blood cells) carry oxygen in
the blood. The biconcave disc shape provides a
large surface area for gas exchange. They have
no nucleus so there’s more room for haemoglobin
(see p. 86), the protein that carries oxygen.
61
how are Epithelial cells specialized?
3) Epithelial cells cover the surfaces of organs.
The cells are joined by interlinking cell membranes
and a membrane at their base. Ciliated epithelia
(e.g. in the airways) have cilia that beat to move
particles away. Squamous epithelia (e.g. in the lungs)
are very thin to allow efficient diffusion of gases.
62
how are sperm cells specialized?
4) Sperm cells (male sex cells) have a flagellum (tail) so they can swim to the egg (female sex cell). They also have lots of mitochondria to provide the energy to swim. The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg.
63
how are Palisade mesophyll cells specialized?
1) Palisade mesophyll cells in leaves do most of the photosynthesis.
They contain many chloroplasts, so they can absorb a lot of sunlight.
The walls are thin, so carbon dioxide can easily diffuse into the cell.
64
how are root hair cells specialized?
2) Root hair cells absorb water and mineral ions from the soil.
They have a large surface area for absorption and a thin,
permeable cell wall, for entry of water and ions.
The cytoplasm contains extra mitochondria to provide
the energy needed for active transport
65
How are Guard cells specialized?
Guard cells are found in pairs, with a gap between them to
form a stoma. This is one of the tiny pores in the surface
of the leaf used for gas exchange. In the light, guard cells
take up water and become turgid. Their thin outer walls and
thickened inner walls force them to bend outwards, opening
the stomata. This allows the leaf to exchange gases for photosynthesis.
66
What is a tissue?
A tissue is a group of cells (plus any extracellular material secreted by them) that are specialised to work
together to carry out a particular function. A tissue can contain more than one cell type.
67
What are four types of animal tissues?
Squamous epithelium cilliated epithelium muscle tissue and cartilage
68
what is squamous epithelial tissue?
1) Squamous epithelium is a single layer of
flat cells lining a surface. It’s found in many
places, including the alveoli in the lungs.
69
what is ciliated epithelium?
2) Ciliated epithelium is a layer of cells covered in
cilia (see page 13). It’s found on surfaces where
things need to be moved — in the trachea for
instance, where the cilia waft mucus along.
70
what is muscle tissue?
3) Muscle tissue is made up of bundles of
elongated cells called muscle fibres. There
are three different types of muscle tissue:
smooth (e.g. found lining the stomach wall),
cardiac (found in the heart) and skeletal
(which you use to move). They’re all slightly
different in structure.
71
What is cartilage?
4) Cartilage is a type of connective tissue found in the joints. It also shapes and supports the ears, nose and windpipe. It’s formed when cells called chondroblasts secrete an extracellular matrix(a jelly-like substance containing protein fibres),which they become trapped inside.
72
What are two types of plant tissues?
Xylem and phloem
73
what is xylem tissues?
1) Xylem tissue is a plant tissue with two jobs
— it transports water around the plant,
and it supports the plant. It contains
hollow xylem vessel cells, which are dead,
and living parenchyma cells.
74
What is phloem tissue?
2) Phloem tissue transports sugars around the plant.
It’s arranged in tubes and is made up of sieve cells,
companion cells, and some ordinary plant cells.
Each sieve cell has end walls with holes in them,
so that sap can move easily through them.
These end walls are called sieve plates.
75
What is an organ?
An organ is a group of different tissues that work together to perform a particular function. Examples include:
76
What do the lungs contain?
• The lungs — they contain squamous epithelial tissue (in the alveoli) and ciliated epithelial tissue
(in the bronchi, etc.(. They also have elastic connective tissue and vascular tissue (in the blood vessels).
77
What do leaves contain?
• Leaves — they contain palisade tissue for photosynthesis, as well as epidermal tissue (to prevent water
loss from the leaf), and xylem and phloem tissues in the veins.
78
What is the respiratory system made up of?
1) The respiratory system is made up of all the organs, tissues and cells involved in breathing.
The lungs, trachea, larynx, nose, mouth and diaphragm are all part of the respiratory system.
79
What is the circulatory system made up of?
2) The circulatory system is made up of the organs involved in blood supply.
The heart, arteries, veins and capillaries are all parts of this system.
