DNA Flashcards
1
Q
How is a dinucleotide joined?
A
Two monomers joined as a result of a condensation reaction between the DEOXYRIBOSE sugar of one and the PHOSPHATE group of the other.
(the bond formed is a phosphodiester bond)
2
Q
What is ribonucleic acid (RNA)?
A
A polymer made up of nucleotides.
3
Q
In RNA, what is the pentose sugar?
A
Ribose.
4
Q
Which 3 individual components are individual nucleotides made from?
A
- pentose sugar
- phosphate group
- nitrogen containing organic base (adenine, cytosine, guanine, or thymine)
5
Q
What are the organic bases in RNA?
A
Adenine, cytosine, guanine and uracil.
6
Q
What is DNA made from?
A
Two very long strands of nucleotides joined together by hydrogen bonds formed between certain bases.
7
Q
Adenine always pairs with…
A
Thymine.
8
Q
Cytosine always pairs with…
A
Guanine.
9
Q
What is said to be the ‘structural backbone’ of DNA?
A
The double helix structure.
10
Q
How is the double helix formed?
A
The phosphate and deoxyribose wound around one another.
11
Q
Does the ratio of A:T and C:G always stay the same or change from species to species?
A
It changes depending on the species.
12
Q
Why is DNA a stable molecule?
A
Because…
• the phosphodiester backbone protects the more chemically reactive organic bases
• as there are 3 hydrogen bonds between C and G, the higher the proportion of C-G pairings, the more stable the DNA molecule
13
Q
What is the function of DNA?
A
DNA is the hereditary material responsible for passing genetic information from cell to cell and generation to generation.
14
Q
How is the DNA molecule adapted to carry out its function? (4)
A
- it is a very stable structure which normally passes from generation to generation without change. only rarely does it mutate
- its two separate strands are joined only by hydrogen, which allow them to separate during DNA replication protein synthesis
- it is an extremely large molecule and therefore carries an immense amount of genetic material
- base pairing leads to DNA being able to replicate and transfer information as mRNA
15
Q
What are the two main stages that DNA replication occurs in?
A
- nuclear division: the process by which the nucleus divides. two main types (meiosis and mitosis)
- cytokines: follows nuclear division and is the process by which the whole cell divides
16
Q
What are the 4 requirements needed for semi conservative replication to take place?
A
- a source of chemical energy
- the enzyme DNA polymerase
- both strands of the DNA molecule to act as a template for the attachment of these nucleotides
- the four types of nucleotide, each with their bases of A, C, G or T present
17
Q
Who discovered the structure of DNA?
A
James Watson and Francis Crick
18
Q
How many hydrogen bonds are there between cytosine and guanine? So what does this mean?
A
- This means that the higher the proportion of C-G pairings, the more stable the DNA molecule is.
19
Q
What is mitosis?
A
The process produces two daughter cells that have the same number of chromosomes as the parent cell and each other.
20
Q
What four stages is mitosis split up into?
A
Prophase, metaphase, anaphase, telophase (PMAT)
21
Q
What three stages is interphase split into?
A
G1, S, G2.
22
Q
What happens during G1?
A
Protein synthesis (cell grows)
Most organelles produced
Volume of cytoplasm increases
Cell differentiation
DNA content: 20 arbitrary
(If cell isn’t going to divide again, it remains in this stage)
23
Q
What happens during S?
A
DNA replication
(the cell only enters this phase if cell division is to take place)
DNA content = 40 arbitrary
24
Q
What happens during G2?
A
Cytoskeleton of cells break down
Protein microtubule components begin to reassemble into spindle fibres - required for cell division
DNA content = 40
25
Where does an increase in mitosis occur?
Wherever an increase in the number of cells is needed.
26
All cells in multicellular organisms originate from...
Stem cells
27
What are neurones (nerve cells) specialised for?
The transmission of electrical nerve impulses.
28
What are stem cells?
Unspecialised cells that divide to become new cells, which then differentiate to become specialised into different cell types.
29
What are red blood cells specialised for?
The carriage of oxygen around the body.
30
What are vascular tissue (xylem and phloem) specialised for?
Transport
31
How are the pentose sugar, phosphate group and organic base joined?
As a result of condensation reactions. This forms a single nucleotide (mononucleotide)
32
What does DNA helicase do?
Breaks the hydrogen bonds linking the base pairs of DNA.
33
Which enzyme allows nucleotides to join together in a condensation reaction?
DNA polymerase.
34
What is nuclear division?
The process by which the nucleus divides.
35
What are the 2 types of nuclear division?
Mitosis and meiosis.
36
What is cytokinesis?
It follows nuclear division and is the process by which the whole cell divides.
37
Before a nucleus divides, why must a cell be replicated (copied)?
To ensure that all the daughter cells have the genetic information to produce the enzymes and other proteins that they need.
38
What are the four requirements for semi-conservative replication to take place?
- the four types of nucleotide
- both strands of the DNA molecule act as a template for the attachment of these nucleotides
- the enzyme DNA polymerase
- a source of chemical energy to drive the process.
39
Three differences between the structure of DNA and RNA?
DNA:
- double structure
- four nitrogen containing nucleobases (adenine, THYMINE, cytosine, guanine)
- long chain of nucleotides
RNA:
- single stranded
- four nitrogen containing nucleobases (adenine, URACIL, guanine, cytosine)
- shorter chain of nucleotides
40
In the cell cycle, where does DNA replication occur?
S (synthesis)
41
What reaction takes place to join a pentose sugar, phosphate group and organic base together? (And what is this called)
A condensation reaction
| A nucleotide
42
What is RNA?
A polymer made up of nucleotides
43
In RNA, what is the pentose sugar?
Ribose
44
What are the organic bases in RNA?
Adenine, cytosine, guanine and uracil
45
What is DNA?
The hereditary material which is responsible for passing genetic material from cell to cell.
46
Why is DNA a stable molecule?
- the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- hydrogen bonds link the organic base pairs, forming bridges between the phosphodiester uprights
47
How does AZTs structure helps?
Because of the similar shape between a thymine containing nucleotide and AZT, the AZT molecule can pair up with the adenine base on the parent strand of DNA.
This stops the replication process by blocking the action of the enzyme controlling the process.
By stoping the viral production, the drug slows down the process of the disease.
48
What does DNA need for replication?
- DNA template
- DNA helicase
- DNA polymerase
- a source of chemical energy
49
What is the structure of DNA vs. RNA?
DNA:
- double stranded
- thymine
- long chain of nucleotides
RNA:
- single stranded
- uracil
- shorter chain of nucleotides
50
How does the cell ensure that it makes the exact copy of the DNA molecule?
Replicating the DNA before the nucleus divides
51
Why is DNA replication known as semi conservative?
Because half of the original DNA strand is converted in the replication process
(A new strand of DNA forms with half of the original strand of DNA matched with a new, copied strand).
52
What is a single nucleotide called?
A mononucleotide
53
What are 2 mononucleotide son joined together called?
A dinucleotide
54
How is a dinucleotide formed?
Two mononucleotides joined as a result of a condensation between deoxyribose sugar of one mononucleotide and phosphate group of the other (forming a phosphodiester bond and a new structure)
55
Difference between DNA and proteins?
DNA is a sequence of bases,
| Protein is a sequence of amino acids.
56
What do amino acids join together to form?
Polypeptide
57
What do DNA join together to form?
Polynucleotide
58
What is the pentose sugar in DNA?
Deoxyribose
59
Who worked on the structure of DNA and when?
1953 - James Watson and Francis Crick
60
Who did the pioneering work for DNA?
Rosalind Franklin
61
How are the two strands of DNA joined together?
Hydrogen bonds formed between certain bases
62
What is nuclear division?
The process by which the nucleus divides
63
What are the types of nuclear division?
Meiosis and mitosis
64
What are the two main stages in which cell division occurs?
Nuclear division and cytokinesis
65
Outline cytokinesis.
It follows nuclear division and is the process by which the whole cell divides.
66
What must happen before the nucleus divides?
It must be replicated (copied)
67
What are the 4 requirements for semi conservative replication to take place?
- the 4 types of nucleotides
- DNA polymerase (enzyme)
- source of chemical energy to drive process
- both strands of DNA molecule to act as the plate for nucleotides
68
Briefly outline the semi-conservative model.
It proposes that the original DNA molecule is split into 2 separate strands, each of which then replicated its mirror image (the missing half). Each of the 2 nucleotides would therefore have one strand of new material and one strand of original material.
69
How many chromosomes are in a human?
There are 46 chromosomes in every human cell (except a sperm cell)
70
Outline the role of mRNA
It transfers the DNA code from the nucleus to the cytoplasm
71
How is the mRNA adapted to its function?
It is small enough to leave the nucleus via the nuclear pore
And it possesses information in the form of codons. The sequence of codons determines the amino acid sequence of a specific polypeptide that will be made.
72
What does 'codon' refer to?
The sequence of three bases on mRNA that codes for a single amino acid.
73
What is the double helix?
Two nucleotide chains would around each other
74
What is a genome?
The complete set of genes in a cell, including those in mitochondria & chloroplasts
75
Define proteome
The full range of proteins produced by the genome
76
In protein synthesis, what are the two types of RNA that are important?
mRNA and tRNA
77
Where does mRNA act as a template for protein synthesis?
In the ribosomes
78
What does tRNA look like?
A single stranded chain folded into a clover leaf shape, with one end if the chain extending beyond the other.
79
In a tRNA molecule, why does one end of the chain extend beyond the other?
Because the longer chain is where the amino acid can easily attach.
80
What are the 4 requirements for semi conservative replication to take place?
- the 4 types of nucleotides
- DNA polymerase (enzyme)
- source of chemical energy to drive process
- both strands of DNA molecule to act as the plate for nucleotides
81
Briefly outline the semi-conservative model.
It proposes that the original DNA molecule is split into 2 separate strands, each of which then replicated its mirror image (the missing half). Each of the 2 nucleotides would therefore have one strand of new material and one strand of original material.
82
How many chromosomes are in a human?
There are 46 chromosomes in every human cell (except a sperm cell)
83
Outline the role of mRNA
It transfers the DNA code from the nucleus to the cytoplasm
84
How is the mRNA adapted to its function?
It is small enough to leave the nucleus via the nuclear pore
And it possesses information in the form of codons. The sequence of codons determines the amino acid sequence of a specific polypeptide that will be made.
85
What does 'codon' refer to?
The sequence of three bases on mRNA that codes for a single amino acid.
86
What is the double helix?
Two nucleotide chains would around each other
87
What is a genome?
The complete set of genes in a cell, including those in mitochondria & chloroplasts
88
Define proteome
The full range of proteins produced by the genome
89
In protein synthesis, what are the two types of RNA that are important?
mRNA and tRNA
90
Where does mRNA act as a template for protein synthesis?
In the ribosomes
91
About what is the side of tRNA?
Relatively small - around 80 nucleotides
92
Briefly say what transcription is.
When a complementary section of DNA that provides the instructions in the form of long sequence bases is made in the form of pre-mRNA
93
How does pre-mRNA change to mRNA?
The pre-mRNA is spliced.
94
Briefly say the idea of translation.
mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked reform a polypeptide.
95
What stage is a cell in if it isn't going to divide?
G
96
In the cell cycle, where does DNA replication occur?
S (synthesis)
97
How does one he cell ensure that it makes an exact copy of the DNA molecule?
By replicating the DNA before the nucleus divides.
98
Why is the process of DNA replication known as semi-conservative?
Because half of the original strand of DNA is conserved in the replication process: q new strand of DNA forms with half of the original strand of DNA matched with a new, copied strand.
99
The AZT molecule might become incorporated into the DNA during replication by pairing up with the adenine base on the parent strand of DNA (due to its similar shape to thymine. What does this do?
This stops the replication process because it blocks the action of the enzyme controlling the process.
100
What does transcription do in prokaryotic cells?
Transcription in prokaryotic cells results directly in the production of mRNA from DNA.
101
In eukaryotic cells, what does transcription result in?
The production of pre-mRNA which is then spliced to form mRNA.
102
Why is splicing of prokaryotic cells unnecessary?
Because they don't have introns.
103
What is contained within the DNA of a gene eukaryotic cell?
Exons that code for proteins and codons (that don't)
104
What do the intervening introns do?
Prevent the synthesis of a polypeptide.
105
What happens in splicing?
The base sequences corresponding to the introns are removed and the functional introns and the functional exons are joined together.
106
Once the mRNA has been spliced, why do they leave via nuclear pores?
Because they are too large to leave via diffusing out of the nucleus.
107
What is a gene?
A section of DNA that contains the coded information for the amino acid sequence of a polypeptide and functional RNA.
108
In genes, what is coded information in the form of?
A specific sequence of bases along the DNA molecule.
109
What polypeptides make up?
Proteins
110
Enzymes are...
Proteins
111
In genes, what do enzymes control?
Chemical reactions
112
Because enzymes control chemical reactions in genes, what are they responsible for?
An organism's development and activities.
113
What is the name of where a gene is located?
Locus
114
What does DNA code for?
Amino acids
115
Why did scientists suggest that there must be a minimum of 3 bases to code for each amino acid?
* only 20 different amino acids that regularly occur in proteins
* using a pair of bases, 16 (4 squared) different codes are possible (but inadequate)
* using three bases, 64 (4 cubed) different codes possible - more than enough to satisfy requirements of 20 amino acids
* only 4 bases (A, C, G, T) present in DNA
* if each base coded for an amino acid, only 4 amino acids could be coded for
116
What is a triplet?
Three bases that code for an amino acid.
117
In the genetic code, how many possible triplets are there?
64
118
In the genetic code, how many amino acids are there?
20
119
What does the 'non overlapping genetic code mean'?
Each base in the sequence is read only once.
120
What from the genetic code is indirect evidence for evolution?
The fact that the code is universal with a few minor exceptions that each triplet codes for the same amino acid in all organisms.
121
What does the term 'codon' refer to?
The sequence of three bases on mRNA that codes fora single amino acid.
122
What is a genome?
The complete set of genes in a cell, including those in mitochondria and / or chloroplasts
123
What is a proteome?
The full range of proteins produced by the genome.
124
Describe the role of RNA polymerase in transcription.
It moves along the strand and joins the nucleotides to form a pre mRNA molecule.
125
Describe the role of DNA helicase in transcription.
To separate out the hydrogen bonds.
126
What is cancer?
An uncontrolled cell division which causes malignant tumours.
127
What are the four types of treatments for cancer?
Chemotherapy, radiotherapy, hormone therapy and biological therapy.
128
What's metastatis?
When some of the tumour cells break free from the tumour and start flowing through the body and circulate in the blood stream. This can cause a secondary tumour and is harder to treat.
129
Why are bacteria slimy?
They have it as protection from being damaged by other organisms.
130
State the differences between parent and daughter cells in mitosis.
There aren't any - they're identical.
131
If you started with 1, how many cells would you have after 2 round of mitosis?
4
132
What is a carcinogen?
Something that increases the risk of cancer / damages DNA.
133
What about a virus makes you feel ill?
The cell damage.
134
How can you prove that viruses are not alive?
Use MRS GREN
135
How does down syndrome develop?
There is an imbalance in chromosomes. So, the chromatic will move to the pole on one side, meaning there will be one too many chromosomes on one pole and too little on the other - leading to down syndrome.
136
DNA is a sequence of...
Bases
137
Proteins are a sequence of...
Amino acids
138
Amino acids join to form...
A polypeptide
139
What is the cell cycle affected by?
The availability of nutrients.
140
What is the cell cycle?
The process by which all body cells from multi cellular organisms use to grow and divide.
141
What do "proof reading" enzymes do?
Check the copied chromosomes for any mutations (mistakes).
142
What happens if the proof reading enzymes detect mutations?
The cell may kill itself (commit suicide) in a process called apoptosis.
143
What stages occur in interphase?
G1, S, G2
144
If a cell is not going to divide again, what stage will it remain in?
G1
145
What is the longest stage of interphase?
G1
146
What happens in G1?
Protein synthesis - cell grows
Most organelles produced
Volume of cytoplasm increases
Cell differentiation
147
What happens in S?
DNA replication
148
What happens in G2?
Short gap before mitosis
Cytoskeleton of cell breaks down and protein microtubule components begin to reassemble into spindle fibres - required for cell division.
149
When does mitosis occur?
Wherever an increase in the number of cells is needed.
150
What kind of reproduction does mitosis occur?
Asexual
151
How is differentiation achieved?
Due to the switching on and off of certain genes
152
Using an example, explain non-overlapping.
Six bases numbered 123456 are read as triplets 123 and 456, rather than 123, 234, 345, 456.
153
Three triplets don't code for any amino acid. What are these?
Stop codons.
154
What do stop codons do?
Mark the end of a polypeptide chain.
155
What are exons?
Coding sequences
156
What is a codon?
Three bases (for example ACG) that codes for an amino acid.
157
Name the process that remixes base sequences from pre-mRNA to form mRNA
Splicing
158
Cells lining the human intestine complete the cell in a short time. Explain the advantage of these cells completing the cell cycle in a short time.
More cells are reproduced in a shorter space of time.
159
How do nucleotides join together?
By a condensation reaction.
160
What is DNA made from?
2 polynucleotide strands held together by hydrogen bonds between complementary base pairs.
161
2 important enzymes in semi-conservative replication?
DNA helicase and DNA polymerase
162
In semi-conservative replication, what does DNA helicase do?
It breaks the (h)ydrogen bonds between the bases on the 2 DNA strands. This makes the helix unwind into 2 single strands.
163
In semi-conservative replication, what does DNA polymerase do?
Catalyse the condensation reactions which join the new nucleotides tigether.
164
What is the end product of semi-conservative replication?
One strand of the original DNA molecule and one new strand. (x2)
165
Name the purine bases.
Adenine
| Guanine
166
Name the pyramids bases.
Thymine
| Cytosine
167
On a DNA strand, the two strands run in opposite directions. What is this known as?
Anti parallel strands
168
How is DNA stored in eukaryotic cells?
Each DNA molecule is linear and wrapped around histones (which are proteins) and forms a chromosome.
169
Difference between prokaryotic and eukaryotic cells in DNA?
EUKARYOTIC:
- long molecule (ie many genes)
- linear shape, forming part of a chromosome
- more than one different molecules per cell
- associated with proteins (histones)
- has non-coding DNA within genes (introns) and as non-coding multiple repeats between genes
PROKARYOTIC:
- short cell (few genes)
- circular (forming closed loop)
- one kind of molecule per cell
- not associated with proteins
- no non-coding DNA
170
What are the two stages of protein synthesis?
1. Transcription
| 2. Translation
171
The first stage of protein synthesis is transcription. Explain the main steps.
1. RNA polymerase attaches to the DNA double helix at the beginning of a gene.
2. The hydrogen bond between the DNA strands in the gene break, separating the strands and the DNA molecule uncoils - exposing bases.
3. One of the strand is then used as a template to make a mRNA copy.
4. I don't know abs I don't understand
172
Outline semi-conservative replication.
1. DNA helicase breaks the hydrogen bonds between the bases on the 2 DNA strands. This makes the helix unwind to form 2 single strands.
2. Each original strand acts as a template for a new strand. Complementary base pairing means that free floating DNA nucleotides are attracted to their complementary exposed bases on each template strand.
3. Condensation reactions join the nucleotides of the new strands together - catalysed by DNA polymerase.
4. Hydrogen bonds form between the bases on the original and new strands.
5. Now, each new DNA molecule contains 1 strand from the original molecule and 1 new strand.
173
Why is the genetic code described as being universal?
Because in all organisms, the same triplet codes for the same amino acid.
174
The genetic code uses 4 different DNA bases. What is the maximum number of different DNA triplets that can be made using these four bases?
64
175
The genetic code is described as being degenerate. What does this mean?
An amino acid can be coded for by more than one triplet.
176
What is a codon?
A codon is 3 bases (eg ACG) that codes for an amino acid.
177
mRNA. An be converted to cDNA. Name the enzyme used in this process.
Reverse transcriptase.
178
DNA helicase is important in DNA replication. Explain why.
In semi-conservative replication, there's a strand of DNA and DNA helicase breaks the hydrogen bonds between the nucleotide bases. This creates 2 separate strands of DNA so that free nucleotides can join onto each other to create 2 identical strands.
179
Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cell completing the cell cycle in a short time.
More cells are reproduced in a shorter space of time.
180
In which stage of the cell cycle are mutations most likely?
Interphase 1
(Not interphase 2 because in that stage, DNA is not replicated.
181
What can DNA code for?
Either a polypeptide or functional RNA.
182
What is functional RNA?
RNA that isn't translated into proteins.
183
Non-coding sections of DNA might be...
- between genes. these sections include genes that are repeated over and over again; often called non-coding repeats.
- within genes. these non-coding sections of DNA are called introns and they separate the coding sequences called exons.
184
What is splicing?
In eukaryotic cells, and in pre-mRNA, the base sequences corresponding to the introns are removed and the functional exons are joined.
This happens, then the mRNA leaves the nucleus.
185
Does splicing occur in...
- eukaryotes
- prokaryotes
Eukaryotes
186
Why doesn't splicing occur in prokaryotes?
Because most prokaryotes don't have introns; so splicing would be unnecessary.
187
Difference between ribose and deoxyribose?
Deoxyribose is the sugar ribose but with one oxygen atom missing
188
What kind of charge does the phosphate group in a nucleotide have?
The phosphate group has a negative charge, which makes DNA a highly charged molecule.
This negative charge enables us to separate fragments of DNA by a technique called 'electrophoresis'.
189
Difference between DNA and proteins?
Proteins are a sequence of amino acids, whereas DNA aims a sequence of bases.
190
What does it means that the genetic code is non-overlapping?
Base triplets don't share their bases.
191
What does it mean that the genetic code is degenerate?
There are more possible combinations of triplets than there are amino acids (20 amino acids but a possible 64 triplets).
192
What does it mean that the genetic code is universal?
The same specific base triplets code for the same amino acids in all living things.
193
Outline the differences in the outcomes of mitosis and meiosis.
Meiosis produces 4 daughter cells. Mitosis produces 2 daughter cells.
Meiosis produces HALF the number of chromosomes as the parent cell, whereas mitosis produces the SAME number of chromosomes.
Meiosis produces genetically different cells. Mitosis produces genetically identical cells to parent cells and each other.
194
What are chromosome mutations caused by?
Errors in meiosis
195
Define gene mutation.
Gene mutation involve a random change in the DNA base sequence of chromosomes.
196
What are the two types of errors in mutation?
Substitution / deletion.
197
Why do not all substitutions (mutations) lead to a change in amino acid sequence?
Because of the degenerate nature of DNA, meaning some codons are coded for by more than one DNA triplets.
So some substations will code for the same amino acid.
198
What affects the rate of mutation?
Mutagenic agents (eg ionising radiation, ultraviolet radiation).
199
What are the three things that the genetic code is said to be?
Non-overlapping, degenerate, universal
200
How many amino acids are there?
20
201
How many triplets are there?
64 (4^3)
202
The genetic code is said to be degenerate. What does this mean?
Most AAs are coded for by more than one triplet.
203
The genetic code is said to be universal. What does this mean?
The same specific base triplets code for the same AAs in all living things.
204
In what way is the genetic code indirect evolution for evolution?
Because the genetic code is universal.
205
The genetic code is said to be non-overlapping. What does this mean?
Each base in the sequence is only read once.
(Eg base triplets not share bases - six bases numbered 123456, are read as 123, 456 rather than 123, 345, 567 etc.
206
Coding sequences are called ________.
Non-coding sequences are called __________.
Coding - exons
Non-coding - introns
207
What is the genetic code?
The sequence of base triplets (codons) which code for specific AAs.
208
What is a nucleotide made from?
- pentose sugar
- nitrogen containing organic base
- phosphate group
209
How are polynucleotides joined?
The nucleotides join via a condensation reaction between phosphate group of on nucleotide and sugar of another.
This forms phosphodiester bond. (Consisting of the phosphate group and two ester bond)
210
Outline semi-conservative replication.
1. DNA Helicase breaks H bonds between two polynucleotide chains, making helix unwind into single strands.
2. Each original strand acts as a template. Complementary base pairing means free floating nucleotides are attracted to their complementary exposed bases (A-T, C-G).
3. Condensation reactions join the nucleotides together; catalysed by DNA polymerase. H bonds form.
4. Each new strand has one new, one old strand.
211
Why are DNA strands always antiparallel?
- the active site of DNA polymerase is only complementary to the 3' end of the newly forming DNA, so can only add nucleotides here.
- this means the template strand goes in a 3' to 5' direction, and new strand goes in 5' to 3' direction.
- because the strands are antiparallel, the DAN polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.
212
What does mitosis produce?
Two genetically identical daughter cells.
213
What is the purpose of mitosis?
Needed for the growth of multicellular organisms.
And repairing damaged tissues.
214
What happens in prophase?
- chromosome become visible. They condense, getting shorter and fatter (chode).
- centrioles move to poles of cells.
- from each of the centrioles, spindles develop.
- nucleolus disappears.
- nuclear envelope breaks down, leaving chromosomes free in cytoplasm.
215
What happens in metaphase?
- chromosomes seen to be make up of 2 chromatids.
- chromatids joined by centromere.
- chromatids line up along the equator (joined by spindle)
216
What happens in anaphase?
- centromere ➗ into 2, separating each pair of sister chromatids
- spindles contract, pulling chromatids to opposite poles of spindle, making chromatids appear V shaped.
- energy for this provided by mitochondria.
217
What happens in telophase?
- chromatids reach opposite poles on the spindle
- chromatids become longer and thinner and are now chromosomes again
- nuclear envelope forms around each group of chromosomes, so now two nuclei
- cytoplasm ➗ (cytokinesis)
218
Give one example of how cancer treatment can target the cell cycle.
Chemo prevents the synthesis of enzymes needed for DNA replication (in G1). If these aren't produced, the cell can't enter the S phase - disrupting the cell cycle and forcing it to kill itself.
219
How can you calculate mitotic index?
Number of cells with visible chromosomes ➗ total number of cells observed.
220
Why do you need to squash the tissue when preparing a slide of plant root tips?
To make the tissue thinner and allow light to pass through.
