nucleic acids Flashcards
(46 cards)
1
Q
what are nucleotides 2
A
- building blocks of nucleic acids such as DNA/RNA. nucleotides are monomers and can join together to form dimers (dinucleotides) and polymers (polynucleotides)
- a nucleic acid is the functional molecule made of one/more polynucleotide chains
2
Q
what are nucleotides made up of 3
A
- pentose sugar= contains 5 carbon atoms
- nitrogenous base= contains carbon and nitrogen
- phosphate group= contains phosphate
3
Q
describe polynucleotides 4
A
- nucleotides are joined together via condensation reactions to form a polynucleotide
- phosphate group of one nucleotide forms a covalent bond with the sugar of another. this forms a phosphodiester bond
- many nucleotides can join in this way to create a chain of phosphates and sugars known as the sugar-phosphate backbone
- phosphodiester bonds can be broken via hydrolysis reactions, releasing the nucleotide monomers
4
Q
whats dna
A
type of nucleic acid that contains instructions needed to make proteins
5
Q
what is dna made up of 3
A
- deoxyribose= pentose sugar
- A, T, C or G nitrogenous base = adenine, thymine, cytosine or guanine
- a phosphate group
6
Q
dna structure 2
A
- 1953, watson and crick credited with working out dna structure
- with the help of other scientists like rosalind franklin, they found that dna is made of 2 polynucleotide chains wound around each other to form a double helix
7
Q
what features of dna allow it to pass genetic info from one generation to another 6
A
- sugar phosphate backbone= protects coding bases on the inside of the helix
- double stranded= allows strands to act as templates in dna replication
- large molecule= stores lots of info
- double helix= makes the molecule compact
- complementary base pairing= allows accurate dna replication
- weak hydrogen bonds= allows strands to separate in dna replication
8
Q
define purines
A
larger bases that contain 2 carbon ring structures (A and G)
9
Q
define pyrimidines
A
smaller bases that contain one carbon ring structure (T and C)
10
Q
complementary base pairing 3
A
- adenine to thymine via 2 hydrogen bonds
- cytosine to guanine via 3 hydrogen bonds
- a smaller pyrimidine base always binds to a larger purine base. this arrangement maintains a constant distance between the 2 sugar-phosphate backbones
11
Q
define RNA
A
type of nucleic acid that uses info from dna to synthesise proteins
12
Q
what is rna made up of 3
A
- ribose= a pentose sugar
- A, U, G, C base
- phosphate group
13
Q
structure of rna 2
A
- contain ribose instead of deoxyribose and the base uracil instead of thymine
- single stranded molecule made of one polynucleotide strand, shorter than dna strands
14
Q
background on dna replication 2
A
- semi-conservative replication
- produces dna molecules consisting of one original dna strand and one newly synthesised dna strand
15
Q
stages of dna replication 4
A
- dna helicase breaks hydrogen bonds between complementary bases. unwinds the double helix and separates the strands
- each strand acts as a template as free nucleotides attract to their complementary bases
- dna polymerase joins the free nucleotides together via condensation reactions in the 5’ to 3’ direction. forms phosphodiester bonds to form the sugar-phosphate backbone of the new dna strand
- 2 identical copies of dna are made, each has one old strand and one new strand
16
Q
meselson stahl experiment
A
after dna’s structure was discovered, few theories were proposed to explain how dna replicates itself during cell division
17
Q
first theory, conservative replication 2
A
- original dna molecule stays intact while a completely new copy is built
- after a single replication one molecule has 2 original strands and the other has 2 new strands
18
Q
2nd theory, semi conservative replication 2
A
- original dna splits, and each strand acts as a template for a new strand
- after a single replication, each dna molecule has one old strand and one new strand
19
Q
what was meselsons and stahls experiment based on 3
A
- dna contains nitrogen
- 2 diff nitrogen isotopes can be used to mark dna strands and track them during replication, 14N lighter and 15N heavier
- bacteria use nitrogen from their surroundings to build new dna molecules
20
Q
experimental process of meselson and stahl experiment 5
A
- bacteria were grown in a medium containing 15N, so all their dna is heavy
- bacteria were transferred to a medium with 14N for one round of replication, so the lighter nitrogen was incorporated into any new DNA strands they made
- DNA was extracted and centrifuged
- steps 2-3 were repeated for another round of replication
- distribution of heavy and light dna were analysed to track how dna was replicating: heavier bands sink lower in the test tube, intermediate bands made of one heavy and one light strand are in the middle of the test tube, lighter bands are higher up in the test tube
- experiment showed that dna replication is semi conservative
21
Q
what happens in the first replication of semi conservative replication 4
A
- the original, heavy dna strands separate
- each heavy strand acts as a template for a new complementary strand
- new, light strands form alongside the original strands
- each resulting dna molecule consists of one old, heavy strand and one new light strand
22
Q
what happens in the 2nd replication of semi conservative replication 4
A
- both original strands and 2 new strands act as templates
- new, light strands form alongside all 4 templates
- half the new molecules have one old strand and one new strand
- other half made of completely light strands
23
Q
structure of ATP
A
nucleotide derivative consisting of ribose, adenine and 3 phosphate groups
24
Q
uses of ATP in the body 5
A
- movement, such as muscle contraction or for sperm cells to swim
- active transport of molecules against the conc gradient, such as ions entering plant roots
- synthesis of large molecules, such as dna/proteins
- secretion of substances from cells, such as releasing hormones from glands
- activate molecules by phosphorylating them. when ATP is hydrolysed, the phosphate can be added to other molecules such as enzymes to make them more reactive
25
how is ATP broken down and resynthesised 2 (examples of reversible reactions)
1. hydrolysis = addition of water to break a chemical bond between 2 molecules
2. condensation= removal of water to form a chemical bond between 2 molecules
26
hydrolysis of ATP to release energy 2
1. when water is added to ATP, it breaks down into adenine diphosphate (ADP) and inorganic phosphate (Pi)
2. this reaction is catalysed by ATP hydrolase and releases energy for use in cells
27
condensation reaction to reform ATP 3
1. when a phosphate group and ADP join, a water molecule is released
2. this reaction is catalysed by ATP synthase
3. this process requires energy and traps chemical energy in the bond
28
features of atp that allow it to work well as an immediate energy source 6
1. hydrolysis of atp releases a little bit of energy meaning less energy is lost as heat
2. atp broken down in one step, meaning energys released quickly
3. atp is rapidly re-synthesised so that its always readily available
4. inorganic phosphate from atp hydrolysis can phosphorylate other compounds making them more reactive
5. bonds between the phosphate groups are unstable, low activation energy and easily broken
6. atp is soluble so can be easily transported around cells
29
structure of water 2
1. a molecule of h2o is made up of one oxygen atom joined to 2 hydrogen atoms. atoms held together by 2 covalent bonds
2. oxygen shares one electron with each hydrogen atom while each hydrogen atom shares its one electron with oxygen
30
water is a dipolar molecule 2
1. shared electrons are pulled towards the oxygen atom, gives it a slightly negative charge. leaves hydrogen atoms with a slightly positive charge
2. water has both positive and negative poles, making it a dipolar molecule
31
water molecules can form hydrogen bonds 3
1. each water molecule consists of a partially negative oxygen end and a partially positive hydrogen end. causes water molecules to interact with each other
2. partially positive hydrogen end attracts the partially negative oxygen end of another molecule. this force of attraction is known as a hydrogen bond
3. hydrogen bonds form between many water molecules, causing them to stick together and giving water some of its useful properties
32
functions of water 6
1. solvent = many substances dissolve in water
2. temp control = water can buffer sudden temp changes
3. cooling mechanism = mammals use the evaporation of water in sweat to cool the skin
4. habitat = many organisms can survive and reproduce in water
5. metabolite = involved in condensation and hydrolysis reactions, make and break chemical bonds between molecules
6. transport = organisms can use water to move substances through osmosis
33
water as a solvent 3
1. many substances within cells are ionic compounds, they consist of positive and negative ions. when these compounds are added to water, their ions split
2. as water is polar, the slightly negative oxygens are attracted to the positive ions while the slightly positive hydrogens are attracted to the negative ions
3. each ion is surrounded by water molecules and the compound dissolves
34
whys water known as the universal solvent
dissolves more substances than any other liquid
35
how is this useful 2
1. most biological reactions take place in solution= cytoplasm of eukaryotes and prokaryotes
2. dissolved substances can be transported around the body= ions can be transported in the blood plasma
36
water as a temp buffer 3
1. water has a high specific heat capacity, means alot of energy needed to raise the temp of one gram of water by 1 degree
2. the many hydrogen bonds between water molecules can absorb alot of energy before being broken so it takes alot of energy to break the hydrogen bonds and heat the water
3. high shc means its resistant to rapid changes in temp. as many organisms are made up of water, this allows the body to remain at a stable temp
37
water as a cooling mechanism 3
1. hydrogen bonding between water molecules means that alot of energy is needed to evaporate 1 gram of water
2. this means water has a high latent heat of vaporisation (high BP). alot of energy required to break the hydrogen bonds to change it from a liquid to a gas
3. useful for organisms bc they can use evaporation of water as a cooling method without losing to much water. when water evaporates from the surface of the skin, it takes heat energy away from the surface, cooling the organism down
38
water as a habitat 3
1. since water has a high specific heat capacity and high latent heat of vaporisation, it doesnt change temp or evaporate easily. provides a stable environment for organisms to live in
2. however, at low temps, water freezes to form ice. water molecules are held further apart in ice, making it less dense then water
3. this causes ice to float, forming an insulating layer at the surface of ponds and lakes. this means the water below the layer doesnt freeze, allowing organisms within the water to move and survive
39
water as a transport medium 4
1. tendency of water molecules to stick together via hydrogen bonds is called cohesion. water also has a tendency to stick to other materials, known as adhesion
2. strong cohesion and adhesion helps water flow through organisms, carrying substances along with it
3. e.g.= cohesion and adhesion allow plants to transport water through the xylem in a continuous column
4. in the same way, when water molecules meet air they create a high surface tension. this forms a skin-like structure at the surface of the water which is strong enough to support small organisms such as pond-skaters
40
define inorganic ions 2
1. ions that dont contain carbon
2. occur in solution in the cytoplasm and body fluids in organisms, some in high conc and others in very low conc
41
define cation
positively charged ions
42
define anion
negatively charged ions
43
explain hydrogen ions 2
1. determine the pH of substances such as blood
2. the higher the conc of hydrogen ions the lower the pH
44
explain iron ions 2
1. component of haemoglobin which is an oxygen carrying molecule in red blood cells
2. haemoglobin binds with oxygen and transports it
45
explain sodium ions 4
1. co-transport of glucose/ amino acids into cells
2. bc sodium is moved out by active transport
3. creates a sodium conc gradient
4. this affects osmosis
46
explain phosphate ions 3
1. used to produce atp
2. phosphorylates other compounds making them more reactive
3. hydrophilic part of phospholipid bilayer
