Major Processes Flashcards
1
Q
Describe what happens in DNA replication
A
- DNA replication is the synthesis of daughter DNA from parental DNA
- Semiconservative process
- Complementary base pairing
- Occurs during the S phase of interphase
- Helicase separates the DNA strands
- Helicase uses ATP to break hydrogen bonds between complementary base pairs
- Unpaired nucleotides on each strand are used as a template to create two double-stranded DNA molecules identical to the original
- Free-floating nucleotides attach to the single strand
- Nucleotides are covalently bonded together (catalysed by DNA polymerases)
- DNA polymerase catalyses the covalent phosphodiester bonds between sugars and phosphate groups
- DNA polymerase III adds DNA nucleotide triphosphates to RNA primer sequence in 5’ to 3’ direction
- Replication on leading strand is continuous
- Replication on the lagging strand is more complex as DNA polymerase III moves in the opposite direction to helicase
- RNA primers are used to mark positions
- DNA polymerase I moves along the replication fork and removes the primers
- DNA ligase attaches the Okazaki fragments together
- DNA gyrase moves in advance of helicase and relieves strain and prevents supercoiling
- Primase synthesizes RNA primer
2
Q
Describe what happens in transcription
A
- Transcription is the synthesis of RNA using DNA as a template
- Occurs in the nucleus
- RNA polymerase binds to a site on the DNA at the start of the gene
- Transcription occurs in a 5’ to 3’ direction
- RNA polymerase add the 5’ end of the free RNA nucleotide to the 3’ end of the growing pre-mRNA molecule by covalently bonding ribonucleoside triphosphates
- There are 3 steps; initiation, elongation, termination
- Initiation: RNA polymerase attaches to DNA at the promoter
- Promoters are non-coding sections of DNA
- The DNA opens and a transcription bubble forms
- Elongation: RNA polymerase synthesizes a RNA strand in a 5’ to 3’ direction
- Creates RNA anti-parallel to template DNA strand
- The transcribes strand is called the anti-sense strand
- Termination: RNA polymerase reaches the transcription terminator signal on the DAN which dislodges the growing RNA strand and RNA polymerase
- Double helix reforms
- RNA molecules can be transcribed from the same gene simultaneously
3
Q
Describe what happens in translation
A
- Protein synthesis using mRNA molecules as a template
- Initiation: mature mRNA binds to the small subunit of the ribosome
- 5’ to 3’ direction until it reaches a start codon
- A molecule of tRNA binds to the p site of the ribosome
- Elongation: a second tRNA molecule then binds to the A site
- The amino acid carried by the tRNA in the P site is transferred to the amino acid in the A site
- A peptide bond forms between the two amino acids
- The tRNA in the P site moves to the E site and is released
- The tRNA in the A site moves to the P site
- Another tRNA complementary to the next codon on the mRNA binds to the A site
- Translocation occurs during elongation
- When as stop codon is reached, translation terminates
- A release factor binds to the A site
- The polypeptide chain is released
- The ribosome complex dissembles
4
Q
Outline photosynthesis
A
- Transformation of light energy into chemical energy
- Photosystems are protein complexes involved where chlorophyll absorbs light energy from photosynthesis
- Found in thylakoid membranes
- Photosystem 1: reaction centre activated by light of wavelength 700 (P700)
- Photosystem 2: reaction centre activated by wavelength of 680 (P680)
5
Q
What happens in the light dependent reaction
A
- Light energy is converted to chemical energy in form of ATP and reduced NADP
- A photon of light is absorbed by a pigment in photosystem 2
- Energy is passed between pigment molecules until it reaches chlorophyll a (P680) in the reaction centre
- The photon excites one of the chlorophyll a electron to a higher energy state
- Two electrons are boosted out of two chlorophyll molecules in the reaction centre
- First electron carrier accepts the two energised electrons
- Electrons pass through ETC
- Energy released from ETC is used to pump H+ into thylakoid lumen from the stroma
- The H+ concentration gradient used to drive ATP synthesis
- A photon of light is absorbed by a pigment in photosystem 1
- Energy is passed between pigment molecules until it reaches chlorophyll a (P700) in the reaction centre
- Two higher energy electrons are boosted out of two chlorophyll molecules in the reaction centre
- Electrons lost in PS1 replaced by electrons in PS2
- NADP+ and H+ combine to form NADPH
- H+ obtained from splitting of water which maintains the flow of electrons through the photosystem
6
Q
What happens in the light independent reaction
A
- ATP and NADPH produced in light dependent reaction are used in light independent reaction
- Occurs in stroma of chloroplasts
- Rubisco catalyses attachment of CO2 to RuBP
- Forms an unstable 6C compound
- 6C splits into 2 G3P
- Each G3P receives one phosphate from ATP
- Each phosphorylated G3P is reduced by NADPH
- 2 molecules of triose phosphate (TP)
- For every 6 molecules of TP one goes to form glucose
- The 5 remaining molecules of TP are used to regenerate RuBP (requires ATP)
7
Q
What is cell respiration
A
- Set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients to ATP, and then release waste products
- glycolysis
- link reaction
- Krebs cycle
- ETC
- Chemiosmosis
8
Q
What occurs during glycolysis
A
- Starts with 2 ATP molecules
- Occurs in cytoplasm
- A hexose sugar is phosphorylated using ATP and split into two triose phosphates
- Oxidation occurs removing hydrogen
- Hydrogen is used to reduce NAD to NADH
- 2 NADH produced
- Net gain of 2 ATP
- 2 pyruvate molecules are produced
9
Q
What happens during the link reaction
A
- Pyruvate enters mitochondrion matrix
- Enzymes remove one carbon dioxide and hydrogen from pyruvate
- Hydrogen is accepted by NAD+ to form NADH
- Oxidative decarboxylation
- Product is an acetyl group which reacts with coenzyme A
- Acetyl CoA enters Krebs cycle
10
Q
Describe the Krebs cycle
A
- Acetyl CoA enters Krebs cycle
- Acetyl group joins 4C to from 6C sugar
- Oxidative decarboxylation of 6C forms a 5C and releases CO2
- Oxidative decarboxylation of 5C forms a 4C and releases CO2
- NAD+ and FAD are reduced by the addition of hydrogen
- Two CO2 produced for each pyruvate
- 3 NADH + H+ and one FADH2 for each pyruvate
- One ATP for each pyruvate per cycle
- NADH and FADH2 produce electrons of ETC
11
Q
Outline the vents that occur during the electron transport chain
A
- Inner membrane of mitochondria and membrane of cristae
- Produces up to 34 molecules of ATP
- First stage of aerobic respiration that requires oxygen
- Series of redox reactions that occur via electron carriers
- Electron carriers are positioned close together which allows electrons to pass from carrier to carrier
- Cristae of mitochondria are impermeable to protons, so electron carriers are needed to pump them across the membrane to establish a proton concentration gradient
- Electrons that enter ETC come from reduced NAD and FAD
- Protons are released when electrons are lost
- Returning protons down the concentration gradient to the matrix gives energy required for synthesis of ATP
12
Q
Outline Chemiosmosis
A
- Energy from ETC allows the addition of a phosphate to ADP to produce ATP
- Involves movement of protons to provide energy so phosphorylation can occur
- Oxidative phosphorylation
- H+ ions accumulate in the inter-membrane space creating a concentration gradient
- H+ moves back into matrix through ATP synthase down the electrochemical conc gradient
- Oxygen is the final electron acceptor
- Oxygen combines with H+ ions and electrons to produce water
13
Q
What occurs during interphase in meiosis
A
DNA is replicated to produce chromosomes consisting of two sister chromatids
14
Q
Outline events that occur in meiosis 1
A
The first meiotic division is a reduction division (diploid → haploid) in which homologous chromosomes are separated
- P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
- M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
- A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
- T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
15
Q
Outline events in meiosis 2
A
The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I)
- P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
- M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
- A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
- T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
16
Q
What happens in the carbon cycle
A
- Carbon is found in biosphere
- Carbon is found in the lithosphere
- Sinks: atmosphere, fossil fuels, carbon compounds in consumers, dead organic matter, producers
- Flux: combustion, incomplete decomposition, death, cell respiration, feeding, photosynthesis, egestion
