Final Exam Part 3 Flashcards
1
Q
Bacterial cell division
A
- Bacteria divide by binary fission. One cell dividing into two. The cells grow, elongate and pinch off in the middle. Exponential process.
- Copy DNA. Chromosomes duplicate themselves.
- When DNA is replicated the machinery starts at the origin of replication where the DNA is copied.
- In bacteria the origin of application gets stuck at one end of the cell. As the chromosome is copied, one stays anchored and one is moved to the other end of the cell.
- So we have one chromosome in one new cell and one chromosome in the other new cell.
- Then the membrane pinches off down the middle to make two new cells. Then has to make new cell wall where the site is divided.
- The protein FtsZ forms a ring around the cells pinching them off. It also divides plastids and mitochondria
2
Q
How does the bacterial cell make sure that the organelles have divided?
A
Bacterial cells have no organelles
3
Q
Eukaryotic cell cycle
A
- There are 4 different phases
- Interphase - 3 sub phases
- G1 phase – growth phase one – growing making more lipids, carbs. Then the cell decides if it will go to the cell cycle or not. Increase in cell size and organelles
- S phase – synthesis phase – synthesis of DNA. DNA has to be duplicated, happens before halfway in the cell cycle. DNA has to be tightly packed and only in its most compact form just before the cell divides. DNA is copied.
- Followed by G2 phase – growth phase 2. Makes the cell larger. Growth phases take up most of the cell cycle.
- M phase – mitotic phase – made up of two different processes – overlapping – mitosis and cytokinesis.
- G1, G2 , S phase = interphase.
4
Q
Eukaryotic cell cycle control/regulation
A
- checkpoints occur in the cell cycle and if the correct “go ahead” signal is missing the cycle does not proceed.
- there are G1, G2 and M checkpoints
- Checkpoint p G1 – is the environment favourable
End of G2 phase – is the cell grown enough, ahs the DNA been copied properly. Any mutations?
In the idle of mitosis – are the DNA ready to be divided?
- Mainly about checking the DNA. Why is DNA most important? Because it codes for everything else, if we make mutations in DNA it may be functioning wrong and then the cell could become a cancerous cell.
5
Q
S phase
A
- Duplication of DNA
- Chromosome is duplicated to make 2 chromosomes. Joined at the centromere. Chromatids, two copies of the same DNA – sister chromatids.
6
Q
Chromatids and centromere definition
A
- chromatids are single copies of a chromosome
- centromere - the specialised region of a chromosome where two sister chromatids are most closely attached
- chromatid - after DNA replication, a chromosome consists of two sister chromatids connected along their entire length.
7
Q
Mitosis
A
- splitting the nucleus and DNA
- mitosis is a nuclear division where two daughter cells gain genetic information
- asexual reproduction
- produces genetically identital offspring with no mechanisms of diversity
- mitosis is a process common to all eukaryotes.
8
Q
Phases of mitosis
A
- I.P.M.A.T
- interphase
- prophase
- metaphase
- anaphase
- telophase
9
Q
Phases of mitosis: interphase
A
interphase - cell is in G2 phase
- chromosomes have replicated - two copies of DNA. everything is duplicated
- nuclear envelope still complete
- centrosomes found together
- no mitotic spindle
- pre-mitotic phase
10
Q
Cytokinesis defintion
A
- The division of the cell is cytokinesis
- division of the cytoplasm
11
Q
Phases of mitosis - prophase
A
The first stage of mitosis. envelopes start ot break apart, the chromosomes are condensing in shape. the mitotic spindles beign to form, pushing the centrosomes to the edge of the cell
changes in cytoplasm
- mitotic spindle begins to form at centrosomes
- centrosomes begin to seperate to opposite poles of cell
changes to nucleus
- chromatin condenses in discrete chromosomes
- nuclear envelope breaks down
- membrane absorbed into the ER
12
Q
Phases of mitosis: metaphase
A
- chromosomes align on metaphase plate
- kinetochores attached to microtubules
- no nuclear envelople.
- centrosomes on opposite ends of the cells.
- the microtubules have connected to the chromosomes to the centromere and the protein complex forms
- chromosomes align in the middle of the cell still stuck together.
13
Q
Phases of mitosis: anaphase
A
- chromatids move to opposite poles
- moved by microtubules and microtubule motors (dyenin and kinesin)
- the chromosomes become detached. the chromatids go to opposite ends of the cell.
14
Q
Phases of mitosis: telophase
A
- chromatin decondenses
- nuclei reform
- spindle disassembles
- nuclear envelope begins to reform
- cytokinesis (cell division) begins during telophase
- telophase is an anti-prophase - everything that happened in prophase is reversed in telophase
15
Q
Formation of mitotic spindle
A
- The microtubules grow from the minus to the plus end. Between the two centrosomes we have a region where the microtubules overlap each other and that where the kinesin and motor proteins. kinesins will walk along the microtubule with cargo., the cargo is also attached to a microtubule. When ATP is added it will move to the plus end, away from the centrosome, slides the microtubules away from each other. Push the centrosomes away from each other.
At the same time dynein, the cargo is the call membrane. It starts walking towards to centrosome, it attaches to the plasma membrane and it will depolymerise at that end and will pull the centrosome towards the plasma membrane. Happens in prophase.
16
Q
Formation of mitotic spindle - metaphase
A
- Attach chromosomes to mitotic spindle. Still pushing but other microtubules will connect on to the chromosomes, one microtubule form one centrosome attached to one chromatid and another microtubule from the other centrosome attached to the other chromatid. During metaphase the chromatids are still stuck together. In anaphase they come apart and they get pulled towards the centrosome. Getting shorter at the microtubule.
- Motor protein going towards the centrosome – dynein, pulling the chromosome towards the centrosome and separates the chromatids.
17
Q
DNA in the stages of cell division
A
- Interphase – nucleolus, doesn’t contain DNA, but does contain RNA
- Prophase – still have a nuclear envelope but chromosomes are starting to condense
- Metaphase – not nuclear envelope, chromosomes are free in the cytoplasm – line up in the middle of the cell. The centromere lines up in the middle. The arms are not attached to the microtubules.
- Anaphase – chromosomes pull apart into two separate collections.
- Telophase – start to condense the chromosomes and the nuclear envelope starts to reform.
18
Q
Microtubules in the stages of cell division
A
- Interphase – microtubules but not in the mitotic spindle.
Prophase – mitotic spindles are forming
Metaphase – no nucleus and lots of microtubules. Thick bundles connected to chromosomes
Anaphase – the bundles of microtubules are gone because they are pulling the chromosomes to each end.
Telophase – lose the spindle arrangement.
19
Q
Animal cytokinesis
A
- animal cells use a cleavage furrow to complete cytokinesis
- occurs at the site of the metaphase plate
- cell divides from outwards inwards
- uses actin microfilaments and myosin
- In animal cells: the cells pinch off in the middle, there’s actin microfilaments (small filaments in the cytoskeleton) – they form a ring between the two cells just under the membrane and it contracts In (myosin walks along the microfilaments using actin as cargo to slide them past each other and make the cell smaller and smaller until it pinches off to make a new cells).
20
Q
Plant cytokinesis
A
- needs to make a new cell wall too
- vesicles from the golgi apparatus fuse to form a cell plate
- cell divides from inside outwards
- uses microtubules and kinesin
- Microtubules left over from the mitotic spindle and they will transport vesicles from the golgi apparatus to the place between the two new cells – the cell plate and they will fuse with each other to form the new plasma membrane forming between the two cells.
- The vesicles contain cargo that will be used – carbs – to use pectin (a component of the cell wall). Contain cellulose synthase – protein that takes sucrose to make cellulose to build a new cell wall. The vesicles make the new plasma membrane and build the new cell wall.
- Vesicles move along microtubule tracks carrying cargo using the motor protein kinesin.
21
Q
Asexual vs. sexual reproduction
A
- Asexual reproduction
- one parent required
- produces genetically identical offspring
- involves mitosis
- sexual reproduction
- two parents required
- produces genetically different offpspring
- involves meiosis
22
Q
mitosis vs. meiosis
A
- mitosis was the division of DNA and nuclei in order to give two full copies of DNA to each daughter cell
- meiosis is division of DNA and nuclei to half copies of DNA to each daughter cell (gametes)
- results in 4 new cells, each cell is genetically different from the parent and each other.
23
Q
Chromosomes of sexual organisms come in…
A
- Chromosomes of sexual organisms come in pairs
- condensed chromosomes can be distinguished by size, banding, centromere position
- pairs = homologus chromosomes
- homologus chromosomes carry the same genes
- exception is the sex chromosomes.
- In mitosis the chromosomes are duplicated/copied resulting into two identical chromatids. You’ll fid another one similar to this one. We call those homologous chromosomes. They are similar but not identical.
- Some might have the same genes coding for eye colour but they have different alleles “variants of gene”. Where one chromosome has the coding for blue eye colour and the other has the coding for brown eye colour – so the chromosomes are similar but not identical. Base pairs are different to give different results of the genes. Not a copy of the chromosomes – these are “sets of chromosomes”
- Homologous chromosomes – sister chromatids are identical copies of the genes.
- The one exception is the sex chromosomes. X chromosome – when counting all the chromosomes in the cell they missed the Y chromosomes because it is so small so they didn’t know what it was so they called the X chromosome. And then they found the Y chromosome and names it the Y chromosome because that’s the next letter after X.
- Y chromosome has its centromere towards one end, once the DNA is duplicated all the way down the length.
24
Q
What is meant by a copy of a chromosome?
A
- Homologus chromosomes - contain the same genes but not identical
- Sister chromatids - identical copies of each chromosome, attached at centromere.
25
Haploid vs. diploid
* Haploid (n) - one set of chromosomes
* Diploid (2n) - two sets of chromosomes
for humans
n = 23
2n = 46
26
Why is meiosis necessary?
* fertilisation doubles the number of chromosomes.
* if we used mitosis the amount of chromosomes would continue to double which wouldn't fit inside a cell.
27
Meiosis in animals vs. plants
* in animals, meiosis produces haploid gametes (sperms and eggs). these fuse to generate diploid offspring that grow through mitosis
* in plants, meiosis produces haploid psores. these spores can divide by mitosis before producing gametes that undergo fertilisation.
* only gametes are haploid in animals
* in bees, the female are diploid and the males are haploid.
28
Phases of Meiosis I
* Prophase I
* Matephase I
* Anaphase I
* Telophase I
29
Phases of Meiosis I: **Prophase I**
* chromosomes condense
* spindle formation - the mitotic spindle forms pushing the centrosomes to opposite sides of the cell. Nuclear envelope breaks down to release the chromosomes.
* A difference to mitosis:
* the homologus chromosomes join together
* The homologous find each other and physically connect to each other and joined at regions calls the chiasmata and a process occurs called crossing over.
* The red switches and becomes the other one so sections of the DNA swap places with each other.
30
Phases of Meiosis I: **metaphase I**
* Chromosomes attach to the mitotic spindle at the kinetochores. Chromosomes align in the middle of the cell at the metaphase plate. But the pairs of homologus chromosomes line up at the middle of the cell. One is attached to one spindle and the other attached at the other.
* A difference to mitosis - homologus chromosomes aligned together.
31
Phases of meiosis I: **anaphase I**
* chromosomes move to the poles
* A difference to mitosis
* homologus chromosomes seperate
* sister chromatids remain attached at centromere
* The chromatids stay attached and instead the two homologous chromosomes separate from each other. They get pulled in opposite directions into the new cells that are forming. Random assortment of chromosomes.
32
Phases of meiosis I: **telophase I**
* Reassembly of the nuclear envelope and disassembly of the mitotic spindle.
* Halving of chromosomes. 3 – 6 chromosomes.
* two haploid cells form, each chromatid is still paired with its sister chromatid.
33
Meiosis II
* Two cells undergo meiosis 2.
* Results in 4 cells with different DNA from the beginning cell, each with half the number of chromosomes form the original starting cell. Non are identical in regards to DNA.
* A difference to mitosis - four haploid cells produce
34
Origins of genetic diversity: **early in prophase I**
* duplicated chromosomes condense
* homologus chromosomes pair in a process called synapsis
* held together by proteins
* In some places they get stitched together by proteins. By synapsis.
35
Why do we need to exchange DNA?
Switching genes switches the combination of phenotypes an individual can obtain. Generates new allele combinations that may be useful in an environment.
36
Crossing over definition
Crossing over = a process where homologus chromosomes pair up during meiosis and exchange segments.
37
Origins of genetic diversity: **middle of prophase I**
* crossing over occurs
* The proteins come and cut the backbone of the DNA and switch it over with the other one and re seal it. Shuffling up the genes, randomly.
* This results in new combinations of genes in each chromatid
* Sister chromatids no longer identical
38
Origins of genetic diversity: **late in prophase I**
* synapsis complex disassembles
* homologues held together at the site of crossing over (chisma, pl. chismata)
* sister chromatids held together at centromere.
39
Origins of genetic diversity: independant assortment
* independant assortment of chromosomes
* The cell doesn't know which chromosomes is from the mother or the father and random assortment results in diversity.
* For a single individual with 46 different chromosomes they have 8.4 million different combinations of chromosomes
40
Summary of origins of diversity
* crossing over - **meiosis**
* independant assortment of chromosomes - **meiosis**
* random fertilisation - **fertilisation**
