Section 1 - Chapter 2: Nucleic Acids Flashcards
1
Q
What are 2 examples of nucleic acids
A
- Ribonucleic acid (RNA)
- Deoxyribonucleic acid (DNA)
2
Q
What are the 3 components that make a nucleotide
A
- A pentose sugar (called because it has 5 carbons)
- A phosphate group
- A nitrogen containing organic base. These are cytosine, thymine, uracil, adenine and guanine
3
Q
How do nucleotides join together
A
- The pentose sugar, phosphate group and organic base are joined in a condensation reaction to form a single nucleotide.
- 2 Mononucleotides can be joined by condensation reactions between the deoxyribose sugar of 1 and phospahte group of the other. This bond is called a phosphodiester bond - dinucleotide
- Continued linking - forms long chain = polynucleotide
4
Q
What is the structure of RNA (ribonucleic acid)
A
- Is a polymer made of nucleotides.
- It is single, relatively short polynucleotide chain.
- Pentose sugar = ribose
- Organic bases = adenine, guanine, cytosine and uracil.
- 1 type of RNA transfers genetic information from DNA to ribosomes. The ribosomes themselves are made up of proteins and another type of RNA. A 3rd type is involved in protein synthesis
5
Q
What is the structure of DNA
A
- In DNA the pentose sugar is deoxyribose and the organic bases are adenine, cytosine, guanine and thymine,
- DNA is made of 2 strands of nucleotides.
- Each of 2 strands is extremely long and joined by hydrogen bonds formed between certain bases.
- Phosphate and deoxyribose molecules alternate to form uprights.
6
Q
What are the base pairing in DNA
A
- The bases on the 2 strands of DNA attach to eachother by hydrogen bonds.
- Adenine pairs with Thymine (complementary)
- Cytosine pairs with Guanine
- Quantities of adenine and thymine = same, quantities of cytosine and guanine = same. However ratio of A,T and C,G vary
7
Q
How does the DNA form a double helix
A
- DNA molecule is formed from 2 separate strands wind around eachother to form a spiral (double helix)
- They form the structural backbone of the DNA molecule (sugar phosphate backbone)
8
Q
What are the differences between RNA and DNA
A
- Shape: DNA is double stranded - twisted into a double helix and held together by hydrogen bonds. RNA is single stranded
- Pentose Sugar: DNA is Deoxyribose sugar and RNA is Ribose sugar.
- Bases: RNA- A,U,C,G and DNA - A,T,C,G
- Size: RNA: relatively short and DNA: long
9
Q
How is DNA a stable molecule
A
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- Hydrogen bonds forms bridges between phosphodiester uprights. 3 hydrogen bonds between cytosine and guanine. 2 hydrogen bonds between A-T. Higher proportion of C-G = more stable
- There are other interactive forces between the base pairs that hold the molecule together (base stacking)
10
Q
How is DNA adapted to carry out its function
A
- Very stable structure - passes generation to generation. Most mutations repaired
- 2 strands joined by hydrogen bonds - allow separation for DNA replication and proteinsynthesis
- Extremely large - carries immense amount of genetic info
- Base pairs with helical cylinder (backbone) - genetic info protected by chemicals/forces
- Base pairing leads to replication and transfer info to mRNA
11
Q
What are the 4 requirements for Semi-conservative replication
A
- The 4 types of nucleotide each with their bases
- Both strands of the DNA molecule act as templates for the attachment of nucleotides
- The enzyme = DNA polymerase
- A source of chemical energy to drive the process
12
Q
How does semi-conservative replication work
A
- Enzyme DNA helicase breaks hydrogen bonds between linking base pairs
- DNA helix separates into 2 strands and unwinds
- Each exposed polynucleotide strand act as a template for complemetary free nucleotides bind by specific base pairing
- Nucleotides are joined together in a condensation reaction by DNA polymerase to form “missing” strand on both originals
- Each of the new DNA molecules contain 1 original strand. Half the original DNA has been saved and built into each of the new DNA molecules
13
Q
What is the other hypothesis called for DNA replication
A
Conservative Model
- Original DNA molecule remained intact and a separate daughter DNA copy was built up from new molecules of deoxyribose, phosphate and organic bases.
- Of the 2 molecules, one would be entirely new material and the other entirely original material
14
Q
What are the 3 facts for Meselson and Stahl’s experiment for semi-conservative replication
A
The based their work on 3 facts:
- All the bases in DNA contain nitrogen
- Nitrogen has 2 forms (isotopes) 14N and 15N (heavier)
- Bacteria will incorporate nitrogen from their growing medium into any new DNA they make
15
Q
What is the Structure of ATP
A
- Adenine
- Ribose
- Phosphates - chain of 3 phosphates
16
Q
How does ATP store enrgy
A
- Bonds between the phosphate groups are unstable and have a low activation energy
- When they break they release energy
- ATP + H20 -> ADP + P (inorganic phosphate) + E
- As water is used to convertATP to ADP - this is a hydrolysis reaction. Catalysed by enzyme ATP hydrolase
17
Q
How is ATP synthesised
A
- The conversion of ATP to ADP is a reversible reaction and energy can be used to add an inorganic phosphate to ADP to re-form ATP.
- Reaction catalysed by ATP synthase - condensation reaction.
- Water is removes - condensation reaction
18
Q
In the synthesis of ATP. The addition of a phosphate molecule to ADP. It occurs in 3 ways.
A
- In chlorophyll containing plant cells during photosynthesis (photophosphorylation).
- In plant and animal cells during respiration (oxidative phosphorylation)
- In plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate- level phosphorylation)
19
Q
Why is ATP used as an immediate energy source rather than glucose
A
- Each ATP molecule releases less energy than a glucose molecule.
- therefore the reactions are smaller/more manageable quantities than glucose
- The hydrolysis of ATP to ADP is a single reaction that releases immediate energy quicker. The breakdown of glucose is a longer series of reactions and therefore energy release takes longer
20
Q
What types of processes is ATP involved in
A
- Metabolic processes - Energy needed to build up macromolecules
- Movement - For muscle contraction
- Active Transport - Provides energy to change the shape of carrier proteins in plasma membrane
- Secretion - Form lysosomes for the secretion of cell products.
- Activation of molecules - the inorganic phosphate released can be used to phosphorylate other compounds to make them more reactive - lowering the activation energy
21
Q
What is Meselson and Stahl’s experiment
(showed DNA replicated by semi-conservative replication. Used 2 isotopes heavy and light nitrogen)
A
- 2 samples of bacteria were grown for many generations. One in nutrient broth with light nitrogen other with heavy. As bacteria reproduced they took up nitrogen.
- A sample of DNA was taken from both and spun in centrifuge. Heavy settled lower from light.
- The bacteria grown in heavy broth taken and put in broth only containing light nitrogen. The replicated and centrifuged
- It turned out DNA settled in the middle showing DNA contained a mixture of light and heavy. If conservative - heavy would be at bottom light at top.
22
Q
What is the importance of water
A
- Important for many metabolic reactions including condensation and hydrolysis reactions
- Water is a solvent, metabolic reactions take place in solution (cytoplasm)
- Helps with temperature control because it has a high latent heat of vaporisation/ specific heat capacity
- Are very cohesive - helps water transport in plants.
23
Q
What is the structure of water
A
- Made of 2 atoms of hydrogen and 1 atom of oxygen
- Oxygen has a slight negative charge while hydrogen atoms have a slight positive charge. - dipolar
- Positive pole of 1 water will be attracted to the negative pole of another water. The attractive force between molecules is a hydrogen bond. Allow water to stick together.
24
Q
Why does water have a high specific heat capacity
A
- Because water molecules stick together
- It takes more energy to separate them then would be needed if they didnt bond
- Without hydrogen bonding - water would be a gas
- It takes more energy to heat a mass of water. Water therefore acts as a buffer against sudden temperature change.
25
What are the different properties of water
* **Important metabolite** in many metabolic reactions, including condensation and hydrolysis reactions
* **Important solvent** in which metabolic reactions occur in
* **Relatively high heat capacity** - buffering change in temperature
* **Relatively large latent heat of vaporisation** - providing a cooling effect with loss of water through evaporation
* **Strong cohesion between water molecules**: supports column of water in transport in plants. Produces surface tension where water meets air.
26
Why does water have a high latent heat of vaporisation and why is this important
* Water evaporates when **hydrogen bonds are broken**
* Allows water on the surface to escape as a gas. It takes a lot of energy to break H bonds - **a lot of energy is used up when water evaporates.**
* This is useful as it means they can use **water loss through evaporation to cool down without losing too much water.** When water evaporates it carries away heat from the surface = cools down
27
What are Inorganic ions
* Ions that dont contain carbon (usually)
* There are inorganic ions in solution in the cytoplasm of cells and in the body fluids of organisms.
* Each ion has a specific role depending on its properties.
* An ions role determines if it is found in high or low concs
28
What are examples of inorganic ions
* **Iron ions in haemoglobin** - The ion binds with the oxygen and releases it to respiring cells
* **Hydrogen ions** - pH is calculated based on conc of H+. More H+, lower the pH.
* **Sodium ions** - Co-transport of glucose and amino acids.
* **Phosphate ions** - Phosphate ion is attached to another molecule its known as a phosphate group. Bond between phosphate groups that store energy in ATP. (DNA, RNA, ATP) Phosphate groups allow nucleotides to join = polynucleotides.
