Cell - Khan Academy Flashcards
1
Q
What is a gamete?
A
A sex cell, either a sperm or an egg cell (ovum).
2
Q
How many chromosomes are there in a human gamete?
A
23 - half of the number of chromosomes in a somatic human cell.
3
Q
How many chromosomes are there in a somatic human cell?
A
46 - 23 pairs
4
Q
What are homologous chromosomes?
A
A pair of chromosomes - one from the father, one from the mother, that code for the same proteins.
5
Q
What is a haploid number?
A
Half of the number of chromosomes. In people, 23. Also: ‘n’ chromosomes.
6
Q
What is a diploid number
A
Full set of chromosomes. In people, 46. Also ‘2n’ chromosomes.
7
Q
What is mitosis?
A
Cell division - replication. Original and divided cells are identical and each has the diploid number of chromosomes.
8
Q
What are germ cells?
A
Cells in the gonads - either ovaries or testes.
9
Q
What is meiosis?
A
Cell division where the original cell is diploid, but produces a haploid cell.
10
Q
How are gametes produced?
A
They are produced by germ cells through meiosis.
11
Q
What are corresponding base pairs?
A
A-T G-C
12
Q
What is DNA replication?
A
When DNA copies itself to make more cells.
13
Q
How does DNA replication work?
A
Two strands separate to become template for each other.
14
Q
How does DNA replication work?
A
Two strands separate to become template for each other.
15
Q
What is DNA transcription?
A
A step in protein production where DNA produces mRNA.
16
Q
What is mRNA?
A
Messenger RNA. A type of single-stranded RNA which is recognized by cell machinery to assemble amino acids into proteins.
17
Q
What is DNA translation?
A
A step where mRNA produces proteins.
18
Q
What is chromatin?
A
A double helix wrapped around structural proteins, e.g. histones.
19
Q
What is a chromosome?
A
A long chains of DNA wrapped around each other.
20
Q
When is DNA shaped into chromosomes?
A
Before cell division. All other time, DNA is working and doesn’t form chromosomes.
21
Q
What are histones?
A
Protein which DNA double helix is wrapped around and which give DNA structure.
22
Q
What is a centromere?
A
When cell divides, each chromosome copies itself, and the resulting pair is connected in the center. The central connection point is called centromere.
23
Q
What is a chromatid?
A
When cell divices, each chromosome copies itself and the resulting pair is connected. The pair is still called a chromosome. Cromatid is one half of that chromosome.
24
Q
What are nucleotides?
A
Basic building block of the nucleic acids - DNA and RNA (in DNA - A, T, C, and G)
25
Where is DNA located in eucaryotes?
In nucleus, mitochondrium, and chloroplasts.
26
Where is DNA located in bacteria?
In nucleoid, which functions similarily to a nucleus, but isn't surrounded by a membrane.
27
What is genome?
A cell's set of DNA.
28
What does it mean that chromatin is decondensed?
For most of the life of the cell, its DNA is not packed into a chromosome, but it forms loose strings.
29
When does chromatin condense?
Condensation takes place when cell is about to divide. It separates to form chromosomes.
30
Which chromosomes are exception to the homologue rule?
Sex chromosomes - X and Y. They are different and carry different genes.
31
What are autosomes?
The 44 non-sex chromosomes.
32
What is a cohesin?
It is a protein that connects sister chromatids.
33
What is interphase?
The major part of a cell's life where it grows and duplicates its DNA.
34
What is cytosol?
The aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.
35
What is the G1 phase?
First gap phase - a phase in the life of a cell where it grows physically larger.
36
What is centrosome?
The main microtubule organising centre (MTOC) in animal cells which plays an important role in cellular function and regulating cell division.
37
What is the S phase?
The phase in the life of a cell where DNA and centrosome are duplicating. (S for synthesis)
38
What is the G2 phase?
The second gap phase - the second growth phase in the life of a cell - after the S phase. It grows, makes protein and organelles, and reorganize its contents in preparation for division.
39
What are the phases in the life of a cell?
1. interphase: G1, S, G2,
2. mitosis or meiosos
40
What is the mitotic phase?
Phase in the life of a cell where it separates its DNA into two sets and divides its cytoplasm, forming two new cells.
41
How does mitosis occur?
The nuclear DNA is duplicated, condenses into chromosomes and is pulled apart by the mitotic spindle, other organelles duplicate, and the cell divides.
42
What is cytokinesis?
Last part of the mitotic phase, starting in anaphase or telophase, where cytoplasm of the cell is split in two and the cell membrane forms.
It happens differently in animal and plant cells.
43
What is a G0 phase?
The resting phase of a cell (not all undergo this phase, eg. rapidly dividing cell in an embryo or a cancer do not). The cell doesn't prepare for division but lives and does its job (e.g. a neuron).
44
What happens in mitotic prophase?
Nuclear membrane starts to disappear, DNA compreses into chromosomes, cytosomes go to opposite sides of the cell and mitotic spindle starts to form, nucleolus disappears.
45
What happens in mitotic metaphase?
Chromosomes are lined up at the metaphase plane, and centromeres start pulling apart at sister chromatids using microtubules.
46
What happens in mitotic anaphase?
Chromatids are pulled apart and migrate to opposite ends of a cell.
47
What happens in mitotic telophase?
Two nuclear membranes start to form around a little bit decondensed chromatids.
48
What is nucleolus.
A part of a cell nucleus, where ribosomes are formed.
49
How does cytokinesis differ in animal and plant cells?
In animal cells, cytokinesis is contractile, and the cell is pinched in two.
Plant cells have a cell wall which is stiff and cannot divide that way. Instead a cell plate is formed in the middle of the two daughter cells.
50
What is cleavage furrow?
The pinch made between two animal daughter cells.
51
What is metaphase plate?
A plane (theoretical, not an actual structure) where all chromosomes are lined up before splitting.
52
What is binary fission?
The process by which bacteria carry out cell division.
53
What are the parts of mitosis - in order?
1. prophase (preprophase and prometaphase)
2. metaphase
3. anaphase
4. telophase
cytokinesis - happens in anaphase/telophase
54
What are the stages of meiosis?
meiosis I
- prophase I
- metaphase I
- anaphase I
- telophase I
meiosis II
55
What is a tetrad?
A homologous pair of chromosomes where each has 2 chromatids.
56
In which phase does the chromosomal crossover (recombination) happen?
In prophase I of meiosis.
57
What is a chiasma?
It's the cross-shaped structure that links homologues together. This is the location where these non-sister chromatids can trade their genetic information.
58
What is chromosomal recombination?
When chromosomes in a homologous pair break up and swap (homologous) sections of DNA between each other.
59
What happens in meiotic anaphase I?
The homologous chromosome pairs separate into two sets.
60
How does mitotic anaphase differ from meiotic anaphase I?
In mitosis, it's the sister chromatids that separate, and in meiosis, it's the homologous pairs.
61
What is interphase II?
A rest period between two phases of meiosis. It doesn't occur in all cells.
62
What are the types of sexual life-cycles?
haploid-dominant
diploid-dominant
alteration of generations
63
Explain diploid-dominant lifecycle.
Somatic cells are diploid, and only sex cells are haploid.
Special diploid cells - germ cells - are made in the gonads early in the embryonic stage. Germ cells undergo mitosis to produce more germ cells, but some undergo meiosis to make haploid gametes. Fertilization restores the diploid state.
Nearly all animals have diploid-dominant lifecycle.
64
Explain haploid-dominant lifecycle.
Mature organisms are haploid. They produce haploid hyphae, which fuse to form zygosporangium whose cells are diploid and are called zygospores.
Under right conditions, zygospores undergo meiosis to make spores - haploid single cells that are released.
Most fungi and some protists have haploid-dominant lifecycle.
65
Explain alteration of generations.
Haploid plants - gametophytes - make gametes using specialized cells. Fertilization creates a diploid zygote.
Zygote undergoes many rounds of mitosis to form a diploid multicellular plant - sporophyte. Specialized cells of the sporophyte will undergo meiosis and produce haploid spores which will develop into gametophytes.
Some algae and all plants have this lifecycle.
66
What are zygospores?
Diploid cells in the haploid-dominant lifecycle, produced by fusing haploid cells of mature organisms.
67
What is zygosporangium
Product of fusing haploid hyphae in haploid-dominant lifecycle.
68
What are spores?
In haploid-dominant lifecycle, spores are haploid single cells created from zygospores by meiosis. They develop into haploid mature organisms.
In alteration of generations, spores are haploid cells which develop into gametophytes.
69
What are gametophytes?
In the alteration of generations lifecycle, these are haploid organisms.
70
What are sporophytes?
In the alteration of generations lifecycle, these are diploid organisms. They produce haploid spores.
71
What is a cell cycle checkpoint?
A stage in the eucaryotic cell cycle at which the cell examines external and internal cues and decides whether or not go forward with division.
72
What is G1 checkpoint?
The main checpoint. A point at the G1 phase, before the S phase, at which the cell decides whether to divide. Entering the S phase means irreversible committment to division.
Checkpoint checks for: cell size, nutrients, growth factors (molecular signals from other cells), DNA damage.
If the checkpoint is not passed, the cell goes into G0 phase.
73
What is G2 checkpoint?
A checkpoint before entering into the M phase.
Checking for: DNA integrity - if DNA isn't damaged, DNA replication - was the DNA copied completely during the S phase.
If there is any damage or errors, the cell will pause G2 to allow for repairs.
If the damage is irreparable, the cell self destructs.
74
What is the spindle checkpoint?
Also known as the M checkpoint. Here the cell checks whether all sister chromatids are correctly attached to the spindle microtubules.
If there is a stray chromosome, the cell witll pause mitosis and wait for the cromosome to be captured.
75
What are cyclins?
They are cell cycle regulators, a group of four basic proteins which promote events for each phase: G1, G1/S, S, M.
76
What are cyclin-dependent kinases? (Cdks)
These are enzymes which are by itself inactive, but are activated by cyclins. The kinases target specific proteins and activate them by attaching a phosphate groups which act like a switch.
77
What is p53?
It is a protein called the guardian of the genome. It works on multiple levels.
It stops the cell cycle at G1 checkpoint by triggering the prodiction of the Cdk inhibitor proteins (CKI).
p53 also activates DNA repair enzymes.
If DNA is not fixable, p53 triggers programmed cell death.
78
What is contact inhibition?
When cells recognize that there are many cells surrounding them and stop mitosis.
79
What is apoptosis?
Cell death.
80
What is a neoplasm?
A group of mutated cells reproducing by mitosis and often forming a tumor.
81
How are cancer cells different from healthy cells?
- they grow without growth factors or trick neighboring cells to produce growth factors for them
- they are not sensitive to contact inhibition
- they display replicative immortality, i.e. replicate more times than is normal (40-60 times for a typical cell)
- they have the ability to metastasise
- they promote angiogenesis - i.e. blood vessel growth
- fail to undergo apoptosis
82
What are oncogenes?
Genes coding positive cell cycle regulators are oncogenes when they're in a version that make the regulators overactive and cancer-promoting.
83
Cancer development stages.
First there are mutations which cause faster cell division. Then, in those rapidly dividing cells, a mutation occurs which inactivates genome stability factor.
84
What are tumor suppressors?
Genes that normally block cell cycle progression in the case of DNA mutations.
85
What is necrosis?
Cell death in response to damage, e.g. injury. Not great, messy, the cell bursts and spills its content. It can cause inflammation.
86
How does apoptosis occur?
Cell gets cues to undergo apoptosis. It shrinks and develops blebs - bubble like protrusions on the surface. The DNA and some organelles get chopped up into small pieces. Entire cell splits into chunks enclosed in a package of membrane.
87
What happens to the remains of a cell which underwent apoptosis?
They release signals which attract phagocytes (type of immune cell) and are eaten by them.
88
What are the reasons for apoptosis?
- Development, e.g. spliting hand into fingers in an embryo.
- Eliminating sick cells, e.g. those with viral infections or with DNA damage.
- Maintaining balance - to make way for new cells or when they no longer have purpose - e.g. immune cells after an infection has been stopped.
89
What are the three differences between prokaryotic and eyukaryotic cells?
1. Eukaryotic cells have a nucleus - a membrane-bound chamber where DNA is stored - while prokaryotic cells don't.
2. Eukatyotic cells usualy have other membrane-bound organelles, while prokaryiotes don't.
3. Prokaryotic cells are much smaller.
90
Prokaryotes: What is a capsule?
It's a sticky outermost layer usually made of polysaccharides.
91
What is the role of capsule in prokaryotes?
It helps prokaryotes cling to each other and to various surfaces in their environment, helps prevent the cell from drying out, and may also protect a pathogen against a host organism's immune system.
92
What is the role of prokaryotic cell wall?
It maintains the cell's shape, protects the cell interior and allow it to take up water.
93
What is the difference between bacteria cell walls and those in plants or fungi?
Plant cell walls are made of cellulose, fungi cell wall - from chitin, while prokaryotic walls are made of sugar-polypeptide polymer named peptidoglycan.
94
What are the outer elements of prokaryotic cells?
From inside to outside:
- plasma membrane
- cell wall
- capsule (optional)
- appendages (usually)
95
What is the role of appendages in prokaryotes?
They allow the cell to stick to surfaces, move around, or transfer DNA to other cells.
96
What are fimbriae?
A type of a prokaryotic appendage - filaments that help cells stick to objects and surfaces.
97
What are pili? What are their roles?
Appendages longer than fimbriae which come in several types:
- sex pilus - holds two cells together and allows DNA to be transfered
- type IV pili - help the bacterium move around its environment
98
What is conjnugation in prokaryotes?
Process of transferring DNA between two bacteria cells.
99
What is a flagellum?
It's a tail-like structure which allows bacteria to move.
100
What is the characteristic of prokaryotic chromosomes?
Most prokaryotes have one circular chromosome.
101
What is a nucleoid?
The part of the cytoplasm in a prokaryotic cell where the chromosome is located.
102
What are plasmids?
Small rings of double-stranded extra-chromosomal DNA that are copied independently of the chromosome.
103
What are R genes?
Genes that make bacteria resistant to antibiotics.
104
What is the role of internal compartments in prokaryotic cells?
They sometimes play a role similar to eukaryotic organelles, e.g. they concentrate a substrate around its enzyme.
They can also increase membrane surface area for reactions, e.g. photosynthesis.
