Cellular Respiration Flashcards
how do cells release energy energy
Catabolic pathways release energy by breaking down complex molecules
Aerobic respiration:
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP/heat, ∆G = -2870
Fermentation:
Anaerobically produced ATP
what are Redox reactions
Redox reaction: Reduction-oxidation reactions
Reduction: addition of electron to another substance
Reduced the amount of positive Charge
Oxidation: loss of electron from one substance
Increases amount of positive charge
Xe^- + Y –> X + Ye-
X becomes oxidized, Y becomes reduced
how would a C6H12O6 + 6O2 –> 6CO2 + 6H2O reaction be a redox reaction
In respiration
C6H12O6 becomes oxidized when turned into 6CO2
6O2 becomes reduced to form 6H2O
how do cells process glucose as a redox reaction
Redox Reactions: reduction-oxidation reactions
Oxidation of glucose takes many small steps
Electrons travel with H+ → H, passed on to electron carrier:
what is NAD+ and NADH
NAD+ = Nicotinamide (oxidized form)
NADH = Nicotinamide (reduced form)
$NAD^+ +2H<–>NADH +H^+$
Uses Dehydrogenase as enzyme
how do electrons from NADH reach O2
How do the electrons from NADH finally reach O2?
- Electron transport chain: series of redox reactions
- Controlled release of energy for synthesis of ATP
- Turns 2H + 0.5O2 → H2O
what are the two phases of Glycolysis
Energy Investment Phase:
- 1 Glucose in
- 2 ATP → 2 ADP + 2P
Energy payoff phase:
- 4ADP + 4P → 4ATP
- 2 NAD+ + 4e- + 4H+ → 2 NADH + 2H+
- 2 Pyruvate + 2 H2O out
What are steps 1-3 of Glycolysis
Glucose: C6
- Hexokinase
Add Phosphate
Glucose 6-phosphate: C6-P
- Phosphoglucoisomerase
Convert
Fructose 6-phosphate: C6-P
- Phosphofructokinase
Add phosphate
Fructose 1,6-bisphosphate: C6-PP
what are steps 4-6 of Glycolysis
Fructose 1,6-bisphosphate: C6-PP
- Aldolase
Cleave in two
Glyceraldehyde 3-phosphate ← → Dihydroxyacetone phosphate (DHAP): 2 C3-P
- Isomerase
Convert to only
Glyceraldehyde 3-phosphate (G3P): 2 C3-P
- Triose Phosphate dehydrogenase
transfer e-, add P: 2NAD+ → 2 NADH + 2H+
1,3-Bisphosphoglycerate: 2 C3-PP
what are steps 7-10 of Glycolysis
1,3-Bisphosphoglycerate: 2 C3-PP
- Phosphoglycerokinase
transfer P to ADP, forms ATP
3-phosphoglycerate: 2 C3-P
- Phosphoglyceromutase
Relocate P
2-Phosphoglycerate: 2 C3-P
- Enolase
Forming double bond
Phosphoenol pyruvate (PEP): 2 C3-P
- Pyruvate Kinase
Transfer P to ADP, forms ATP
Pyruvate: 2 C3
describe the Krebs cycle
- Oxaloacetate + Acetyl CoA → Citrate
- Citrate → Isocitrate
- Isocitrate + NAD+ → a-Ketoglutarate + NADH + H+ + CO2
- a-Ketoglutarate + NAD+ + CoA-SH → CO2 + NADH + H+ + Succinyl Coa
- Succinyl Coa + P + GDP* → Succinate + CoA-SH + GTP
- GTP + ADP → GDP + ATP
- Succinate + FAD → Fumarate + FADH2
- Femarate + H2O → Malate
- Malate + NAD+ → Oxaloacetate + NADH + H+
Redox reactions in steps 3, 4, 6, 8
CO2 relased in steps 3, 4
ATP regenerated at step 5
what does the Krebs cycle do
From one Pyruvate molecules you get:
- 3 CO2
- 1 ATP
- 4 NADH
- 1 FADH2
These go into the electron transport chain
what happens in the Krebs Cycle
→ C2 → 2 CO2
→ recycling of C2 acceptor
how does the electron transport chain work
Electron transport chain:
- Proteins organized in multiprotein complexes I-IV
- Organized on inner mitochondrial membrane
- Series of Redox reactions passing down the electrons and H+
- Transport of e- and H+
→ H+ gradient (proton-motive force)
what does chemiosmosis do
Chemiosmosis: after e- transport chain
- ATP synthase uses H+ gradient to produce ATP
how efficient is respiration
Glucose oxidation ∆G = - 2870 KJ/mol
ADP + P → ATP = 30.5 KJ/mol
This results in 34% efficiency when 32 ATP are produced per glucose
what happens to starch, proteins, and fats
Are we only consuming glucose?
- Starch, Glycogen:
- broken down to glucose
- Proteins: amino acids to build new proteins
- Fats: glycerol + fatty acids
how is glycolysis regulated
Glycolysis is regulated by feedback mechanism.
ATP and citrate inhibit Phosphofructokinase , Stimulated by AMP
how does Anaerobic respiration and fermentation work
Anaerobic respiration: final electron acceptor e.g. SO4 2-
Fermentation: no electron transport chain
- Needed sufficient supply of NAD+
what is alcohol fermentation
Alcohol Fermentation
2 Pyruvate from Glycolysis lose CO2 and turn into 2 Acetaldehyde. Which then turns NADH + H+ back into 2 NAD+, and becomes 2 Ethanol. The new NAD+ allows more glycolysis to form 2 ATP
what is lactic acid fermentation
Lactic acid fermentation
2 Pyruvate from Glycolysis regenerate NAD+ and turn into 2 Lactate. The new NAD+ allows more glycolysis to form 2 ATP
who was Rosalind Franklin
DNA structure was uncovered using X-ray diffraction with the aid of Rosalind Franklin, however Franklin is often left out of the history of our understanding of DNA.
describe the structure of DNA
DNA has the structure of a Sugar-phosphate backbone attached to a number of Nitrogenous bases. There are two chains which run antiparallel to each other, and the nitrogenous bases connected via hydrogen bonds.
The bases Cytosine, Thymine, and Uracil and Pyrimidines with one ring.
Adenine and Guanine are Purines with two rings.
A and T have two hydrogen bonds between them, G and C have three.
what affects DNA helix stability
DNA double helix stability is affected by:
- Temperature
- denaturation or melting of the helix
- Cations
- stabilize the helix; reduce charge repulsion of the two strands
- Base mismatched
- destabilize the helix
- Length of the helix
- longer helices are more stable
- Proteins
- histones - positively charge proteins
More H bonds can also make a chain more stable, so more GC pairs
how is DNA organized in eukaryotes
- complex of DNA double helix and proteins called histones
- Loosely packed form of DNA
- DNA replication and gene expression
- the DNA helix is 2nm wide, Nucleosomes are 10 nm wide.
Nucleosomes coil into a 30 nm wide fibre, then looped into a 300 nm wide fibre, which forms a chromosome 1,400 nm wide.
how is DNA organized in prokaryotes
- circular
- supercoiled
what, where, and when is DNA replicated
- what: the copying of DNA sequence
- when: before the cell divides (S phase)some repair-associated DNA replication can go on throughout the cell cycle
- Where: nucleus, mitochondrion, chloroplastand also in test tubesDNA replication in the mitochondrion and chloroplast is not usually tied to cell division
what are the non material requirements for DNA replication
- Requirements
- it must be coordinated with cell cycle
- fidelity of replication must be very highMistakes are mutations
what are the principles of DNA replication
- replication is semi-conservative. Each daughter helix has one old strand, one newly synthesized strand
- new nucleotides are added according to the Watson-Crick pairing rules. Adenine binds to Thymine, and Cytosine binds to Guanine forming base-pairs thorugh hydrogen bonds.
what are the 7 materials needed for DNA replication
- Helicase: unwind parental double helix
- Single-strand binding protein: maintains ssDNA
- Topoisomerase: prevents ‘overwinding’ ahead of replication fork
- Primase: synthesizes RNA primer
- DNA polymerase III: elongates DNA by adding to primer
- DNA polymerase I: removes RNA primer from 5’ end and replaced it with DNA
- DNA ligase: joins strands of DNA
what are the steps of DNA replication
- the helix is unwound
- the helicase unwinds helix ahead of the fork
- Initiates at the origin of replication- short RNA primers are made
- the primers are extended by DNA polymerase
- the region where replication is going on is called a replication fork
- on the leading strand, synthesis is continuous
- on the lagging strand, synthesis is discontinuous
- Okazaki fragments
- Helicase unwinds more helix ahead of the fork
- overwinding is resolved by topoisomerase
how does DNA polymerase work
- DNA polymerase has directionality
- can synthesize new DNA only in the 5’ → 3’ direction (on the new strand)
- must have a 3’ - OH on which to attach a new nucleotide
how are errors in DNA corrected
- errors are mispairings (potential mutations)
- non-Watson/Crick pairings
- . an uncorrecte base-pairing error through another replication cycle
- DNA polymerase corrects mispairings before proceeding
- this is the proofreading function
- it explains why DNA polymerase needs an end to work with - it needs an end of a correctly-paired nucleotide residue
- paired bases that do not fit the active site, that do not have the common geometry of AT and CG pairs are fixed
- the finished helix is scanned for mispairings
what are two examples of mutations in humans
- Sickle cell anemia
- point mutation in gene encoding for hemoglobin
- Huntington’s disease
- (CAG)n repeat in protein-coding region of gene
what is PCR
- Polymerase chain reaction (PCR)
you take an original double stranded DNA segment, heat it to 90º C to separate the DNA strands, the cooled to 50º C to allow primers and DNA polymerase to bind. New DNA strands are synthesized at 70º C.
what are some genetically modified crops
- Nutrition, disease resistance and pharmaceuticals
- “golden” rice or plants with genetically-engineered resistance to diseases, or containing Vitamin A, edible vaccines
- Herbicide resistance
- Allows farmers to spray crop to kill only the weeds
- Pesticide resistance
- kills insects that feed on crops
- Faster growth rate
what is the genetically modified salmon
- first genetically modified animal
- Recently received FNA and Health Canada approval for human consumption
how are proteins made
DNA undergoes transcription to make mRNA, which is translated to make a protein
what and where is DNA turned to protein
What: transcription of DNA to RNA; translation of RNA to protein\
Where: nucleus, cytoplasm, ER, golgi in eukaryotes; cytoplasm in bacteria
what is important for a gene to turn into a protein
- fidelity of mRNA transcript must be very high, mistakes are mutations
- fidelity of protein sequence must be very high
what are the principles of gene expression
- principles
- information in DNA, RNA and protein is colinearlinear sequence of nucleotides in the coding portion of a gene
- linear sequence of nucleotides in mRNA
- linear sequence of amino acids in a polypeptide
- information in DNA, RNA and protein is colinearlinear sequence of nucleotides in the coding portion of a gene
what materials are needed for gene expression
- Materials needed
- RNA polymerase: joins complimentary RNA nucleotides to the 3’ end of RNA transcript
- mRNA: synthesized by RNA polymerase, codes for protein sequence
what are the events in transcription
- Initiation, Elongation, termination
- the helix is unwound
- RNA nucelotides are extended by RNA polymerase
- assembled in the 5’ to 3’ directon
- mRNA transcription is created
how does transcription initiate
- In bacteria
- RNA polymerase binds to promoter
- In eukaryotes
- RNA polymerase binds to transcription factors that are bound to the promoter
how does elongation work in transcription
Elongation of transcript
- 10-20 DNA nucleotides are exposed at one time
- DNA nucleotides pair with RNA nucleotides
- Progresses at a rate of 40 nucelotides/second in eukaryotes
how is transcription terminated
Transcript termination
- In bacteria:
- proceeds through terminator sequence in the DNA and signals the end of transcription
- In eukaryotes
- proceeds through the polyadenylation signal in the pre-mRNA; this is later cleaved off
describe mRNA
- mRNA: synthesized by RNA polymerase, codes for protein sequence
- the genetic code is a triplet code
- Codon: three-nucleotide sequence that specifies a particular amino acid; basic unit of the genetic code
- Linear: bases of mRNA = letters
- unambiguous: each codon specifies only 1 amino acid
- redundant: 18 of 20 amino acids encoded by more than one codon
- universal: same code used by all organisms, with few differences
- AUG = met
- UAA, UAG, UGA = stop
- Codon: three-nucleotide sequence that specifies a particular amino acid; basic unit of the genetic code
- the genetic code is a triplet code
describe tRNA
- tRNA: molecules containing anticodon and amino acid
- anticodons: specific sequence of three nucleotides on tRNA; complementary to a codon triplet on mRNA
describe rRNA
- rRNA: together with protein makes up ribosome
- Ribosome: facilitates coupling of tRNA anticodons with mRNA
what is needed to make a protein from mRNA
mRNA
tRNA
rRNA
ribosome
how does translation initiate
- a tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming a pre-initiation complex
- the large ribosomal subunit binds to the small subunit. The methionine tRNA binds to the first tRNA site on the large subunit.
how does elongation work in translation
- During the elongation stage, amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain.
- Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation.
- Translation proceeds along the mRNA in a 5’ to 3’ direction.
how is translation terminated
- Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
- The A site accepts a protein called a release factor
- The release factor causes the addition of a water molecule instead of an amino acid
- This reaction releases the polypeptide, and the translation assembly then comes apart.
