Chapter 2 - Nucleic Acids Flashcards
1
Q
What is a diploid
A
A cell/organism that has a pair of homologous chromosomes (it has 2 alleles of each gene)
2
Q
What is a gene
A
A sequence of DNA that codes for a protein and therefore a phenotype
Eg blood type
3
Q
What is an allele
A
A different form of a gene
Eg A, B or O
4
Q
What is a genotype
A
The combination of alleles that an organism has
Eg AA, BB etc
5
Q
What is a phenotype
A
The physical expression of the genotype and it’s interaction with the environment
Eg skin colour
6
Q
What is meant by a dominant allele
A
An allele that is always expressed in the phenotype
Eg functional proteins
7
Q
What is meant by a recessive allele
A
Alleles that are only expressed when homozygous
Eg non-functional proteins
8
Q
What is meant by a co-dominant allele
A
Where both alleles are expressed in the phenotype (so phenotype is intermediate)
9
Q
What is meant by homozygous
A
When both alleles are the same
10
Q
What is meant by heterozygous
A
When alleles are not the same
11
Q
What is meant by the locus
A
The position of a gene on a chromosome
12
Q
Where are alleles of a gene placed on a chromosome
A
On the same locus
13
Q
What is meant by monohybrid inherited
A
Inheritance of a characteristic is controlled by only one gene
14
Q
What is meiosis
A
Cell division to form gametes
15
Q
What are gametes
A
Haploid sex cells (sperm and eggs)
16
Q
What is meant by haploid
A
A cell with a single set of unpaired chromosomes
Or
A cell with one of each homologous pair
17
Q
What is meant by diploid
A
A cell with 2 complete sets of chromosomes
Both homologous pairs, one from each parent
18
Q
What is mitosis
A
Cell division for growth and repair
19
Q
How are the number of divisions different in meiosis and mitosis
A
There are 2 in meiosis and 1 in mitosis
20
Q
What are the 2 divisions in meiosis called
A
Meiosis I
Meiosis II
21
Q
How many daughter cells are produced in meiosis
A
4
22
Q
How many daughter cells are produced in mitosis
A
2
23
Q
How can the daughter cells from meiosis be explained
A
They are genetically different to each other
24
Q
Why are daughter cells in meiosis genetically different to each other
A
- Crossing over
- Independent segregation
25
What is meant by crossing over
The exchange of alleles between homologous chromosomes, resulting in a different combination of alleles
26
What is meant by independent segregation
Formation of random combinations of chromosomes in metaphase, instead of homologous pairs
27
How can daughter cells from mitosis be explained
Genetically identical
28
What happens before meiosis takes place
Interphase
29
What happens in interphase
DNA replicates, so rather than just single chromosomes there are now x shaped chromosomes
30
What are sister chromatids
Two parts to a chromosome, that are chromosomes if they are on their one
Identical to each other
31
What is the centromere
The point that joins the sister chromatids in a chromosome
32
What are the stages of meiosis
Prophase
Metaphase
Anaphase
Telophase
33
How many times does each stage of meiosis occur
Twice
34
What happens in prophase I in meiosis
- Chromosomes condense so become visible
| - Nuclear membrane breaks down
35
What happens in metaphase I in meiosis
- Homologous pairs line up next to each other
- Spindle fibres form
- spindle fibres attach centromeres to centrioles
36
What happens in anaphase I
- Homologous pairs are seperated
| - They ate pulled apart to opposite poles as spindle fibres contract
37
What happens in telophase I
- Nuclear membranes form (around each side of chromosomes)
| - Cell divides
38
What happens in prophase II
Nuclear membrane break down
39
What happens in metaphase II
- Chromosomes line up on equator
| - Spindle fibres form, attaching to centromeres and centrioles
40
What happens in anaphase II
- Chromatids separate
| - Pulled towards opposite poles
41
What happens in telophase II
- Nuclear membrane reform
| - 2 Cells divides into 4 daughter cells all together
42
What is a characteristic of daughter cells at the end of meiosis
The are not genetically identical to each other
43
What are nucleotides
The monomers that make up polynucleotides
44
What are examples of polynucleotides
DNA and RNA
45
What does a nucleotide of DNA consist of
Phosphate group
Deoxyribose
Nitrogen containing base
46
Draw a nucleotide of DNA
Circle
Line down to pentagon
Line across to rectangle
47
What are the bases of DNA
Adenine
Thymine
Cytosine
Guanine
48
What are the characteristics of DNA
- It is double stranded (double helix)
- A long polynucleotide
- Carries genetic information which codes for proteins
- Relatively simple structure
49
Draw a nucleotide of RNA
Phosphate group as circle
Ribose sugar (Pentagon)
Rectangular base
50
What does DNA stand for
Deoxyribonucleic acid
51
What does RNA stand for
Ribonucleic acid
52
What are the characteristics of RNA
- Single stranded
- Short polynucleotides
- Transfer genetic codes from DNA in nucleus to ribosomes in cytoplasm
53
What are the bonds between DNA nucleotides
Phosphodiester bonds
54
What are the phosphate group and pentode sugar parts of DNA nucleotides known as in a strand of DNA
Sugar-phosphate backbone
55
How can the structure of DNA be described
Antiparallel
56
What does antiparallel mean
The strands of DNA run in opposite directions
57
What are the bonds between bases called in DNA
Hydrogen bonds
58
What does adenine bond to and how many bonds are there
Thymine
| 2
59
What does cytosine bond to and how many bonds are there
Guanine
| 3
60
What does semi-conservative DNA replication mean
That DNA contains one new strand and one original strand
61
Explain semi conservative DNA replication
- DNA helicase unzips DNA by breaking hydrogen bonds
- Both strands act as templates
- Free DNA nucleotides attach by complementary base pairing
- DNA polymerase joins nucleotides forming phosphodiester bonds (condensation reaction)
- Hydrogen bonds reform
62
What enzyme unzips DNA
DNA helicase
63
What enzyme joins nucleotides together
DNA polymerase
64
What reaction takes place for phosphodiester bonds to form
Condensation reaction
65
Why can DNA polymerase work continuously in just one direction
- DNA is antiparallel
- Nucleotides son each strand are arranged differently
- Active site of DNA polymerase has a specific tertiary structure
- Only substrates with complementary shape/orientation can bind to active site to form enzyme-substrate complex
66
What is a leading strand
A new strand of DNA formed continuously in semi-conservative replication
67
What is a lagging strand
A new strand of DNA formed in segments
68
What is DNA ligase
Enzyme that connects segments together in a lagging strand
69
Describe the method used to prove semi-conservative DNA replication
- Place cultured bacteria in heavy nitrogen (15N)
- Centrifuge this
- Transfer bacteria into light nitrogen (14N), so that new nitrogenous bases cultured show up different to original
- Centrifuge
- Replicate again in light nitrogen
70
How do the method for proving semi-conservative replication actually prove it?
- Starting population is cultured in a growth medium containing heavy nitrogen (nitrogen is in nitrogenous bases)
- when centrifuged one band can be observed
- Cells are transferred to a medium with only light nitrogen (14N)
- After one replication, the DNA was intermediate between 14N and 15N
- This is twice the thickness due to new DNA
- After 2 replications in 14N, intermediate and light bands can be observed
This proves that DNA replication is semi-conservative
71
What is meant by the DNA antisense strand
- The strand of DNA that acts as a template for mRNA
72
What is meant by the DNA sense strand
The strand of DNA that is complementary to the antisense strand and is not used as a template
73
What enzyme is used to unwind DNA
DNA helicase
74
What is created using the antisense strand as a template
Pre-mRNA
75
How will Pre-mRNA be different to the DNA sense strand
It will have uracil instead of thymine
76
What is used to catalyse the addition of a nucleotide on Pre-mRNA (create a phosphodiester bond)
RNA polymerase
77
What happens to the Pre-mRNA polynucleotide after it has been made
Splicing
78
What is splicing
The removal of introns
79
Why are introns removed?
They are non-coding regions
80
What Pre-mRNA is spliced, what is created
mRNA
81
What does ATP stand for
Adenosine triphosphate
82
What is ATP used for
The main energy source to carry out processes in cells
83
Why is ATP useful
- It releases energy in small amounts
- It is broken down in a single reaction so also releases energy quickly
- Can add phosphate to other molecules do they are more reactive
- Is easily resynthesised (reversible reaction)
84
How is ATP formed
ADP + Pi
85
What reaction takes place when ATL is formed
A condensation reaction
86
What enzyme is used form ATP
ATP synthase
87
What reaction takes place when ATP is broken down
Hydrolysis
88
What enzyme is used when ATP is broken down
ATP hydrolase
89
What is ATP made up of
3 phosphate groups
A ribose sugar
Adenine
90
What is ADP made up of
2 phosphate groups
A ribose sugar
Adenine
91
How can hydrolysis of ATP be useful
It can be used to release energy for other reactions in a cell
92
How does hydrolysis of ATP help to provide energy for other reactions in cells
An inorganic phosphate is released to phosphorylase other compounds
- this makes them more reactive
93
What is meant by an inorganic phosphate
It contains no carbon
94
What is meant by phosprylation
Adding phosphate to
95
What is a water molecule made up of
2 hydrogens atoms and one oxygen
96
Water is a _____ molecule
Polar
97
What makes water a polar molecule
It has a positive and negative end
98
Why does water have a negative end
Impaired electrons on the oxygen have a negative charge
99
Why does water have a positive end
Hydrogens‘ electrons is closer to oxygen so has a slightly positive charge
100
Why are water molecules attracted to each other
There are intermolecular forces between molecules formed by poles of the molecules (oxygen of one molecule being attracted to hydrogen of another)
101
What are the main properties of water
- Good solvent
- Metabolite
- Cohesion
- Temperature Control
- High specific heat capacity
- Ice floats on water
102
What is a solvent
A liquid that other substances can dissolve in
103
How is water a good solvent
- Ionic compounds such as sodium chloride are made from positive and negative ions
- Water is polar
- Positive charges of water will add up for negative ions, and vice versa
- Ions will become neutral so leave compound and dissolves
104
What is the importance of water being a solvent
It allows substances to be transported in animals and plants
105
What is meant by a metabolite
It is involved in reactions either as a reactant or a product
106
How is water a metabolite
It is involved in condensation and hydrolysis reactions
107
What is the importance of water being a metabolite to hydrolysis reactions
This allows digestion of large molecules
108
What is the importance of water being a metabolite to condensation reactions
This allows synthesis of important molecules such as proteins
109
What is meant by cohesion of water
The property that makes its molecules attracted to each other
110
How does water have strong cohesion
Due to its polarity, strong hydrogen bonds hold water together, so that mass flow occurs
111
What is meant by mass flow (of water due to cohesion)
It flows as a continuous stream
112
What is the importance of water having strong cohesion
- Transport of substances eg xylem
| - surface tension of water
113
How is water good for temperature control of organisms
It’s has a large latent heat of vaporisation
114
How does the large latent heat of vaporisation of water helps temperature control
- It takes a lot of energy to break hydrogen bonds between the molecules
- Evaporation occurs when water molecules have high kinetic energy
- They take this energy with them as water vapour
- Causing body of water to cool as it has less energy (eg sweating)
115
What is meant by the heat capacity of water
The amount of heat energy needed to increase the temperature of 1kg of water by 1°C
116
How does water have a high specific heat capacity
- Hydrogen bonds between water molecules take high energy to be broken apart
- Meaning water can absorb large amounts of heat before temperature rises significantly
117
What is the importance of water having a high specific heat capacity
- Organisms made up of water increase body temperature slowly
- Aquatic environments remain a stable temperature
118
How does ice float on water
It is less dense than water
119
What is the importance of ice floating in water
- Provide habitat
| - Reflect heat
120
What is an inorganic ion
A compound not containing carbon
121
Where do inorganic ions occur in organisms
- In cytoplasm
| - In body fluids
122
What is an ion
An atom that has lost or gained electrons (has a charge)
123
What are positive ions called
Cations
124
What are negative ions called
Anions
125
What is pH a measure of
Hydrogen ions in a solution
126
What does hydrogen ions effect
- They are very reactive
- So react with proteins
- change tertiary structure
- Change active site
- No enzyme-substrate complex’s
127
Where are iron ions important
In haemoglobin
128
Why is haemoglobin important
Carries oxygen in red blood cells
129
What is haemoglobin
A protein with a quaternary structure (4 polypeptide chains)
130
What are sodium ions crucial for
Co-transport
131
How are sodium ions useful for co-transport
Help other molecules move across membranes eg glucose
132
What are phosphate ions useful for
- Phosphate In ATL, so provide energy
| - Condensation reactions between phosphate groups to form polynucleotides
