IMMS Flashcards
What is the final step of mitosis?
Cytokinesis
What happens in Interphase G1?
no visible activity but the following occurs
• Rapid growth
• Normal metabolic function
• New organelles produced
• Protein synthesis of proteins involved in spindle formation
S (synthesis):
• DNA doubles through DNA replication
• Histone proteins double through protein synthesis ( 2 x as much DNA at end of S)
• Centrosome replication
What happens in Interphase G2?
- Chromosomes condense (coil up and become visible)
- Energy stores accumulate
- Mitochondria and centrioles double
What happens in Prophase?
- Chromatin condenses into chromosomes
* Centrosomes nucleate microtubules and move to opposite poles of nucleus
What happens in Prometaphase?
- Nuclear membrane breaks down
- Microtubules invade nuclear space
- Chromatids attach to microtubules
- Cell no longer has a nucleus
What happens in Metaphase?
• Chromosomes line up along equatorial plane (metaphase plate)
What happens in Anaphase?
• Sister chromatids separate, and are pushed to opposite poles of the cells, centromere
first, as spindle fibres contract
What happens in Telophase?
- Nuclear membrane reforms
- Chromosomes unfold into chromatin
- Cytokinesis begins
What happens in Cytokinesis?
Cell organelle become evenly distributed around each nucleus
• Cell divides into two daughter cells with a nucleus in each and 46 chromosomes
What is the connection between mitosis and malignancy?
Something is defined as malignant if there are too many mitotic figure i.e. lots of dark
nuclei of different sizes
- Number of mitotic figures determine how bad cancer is, the more there are, the worse
it is
What are produced by meiosis?
4 haploid (HALF number of chromosomes i.e. 23) cells produced, which are genetically distinct from each other and the parent cell
What happens in Meiosis 1?
• Chromosome number is halved
• In Prophase 1, crossing over occurs between non-sister chromatids [genes sort
independently thus if 1 gene switches over, doesn’t mean another one will], resulting
in genetic diversity
• In Metaphase 1, random assortment occurs on the metaphase plate - also resulting in
genetic diversity
What happens in Meiosis 2?
Sister chromatids separate
• Haploid cells produced
How many days does male gametogenesis take?
60-65 days
How many sperm per ejaculate?
100-200 million
How many times must a primordial germ cell mitose to become an oogonia?
30
When do Oogonia enter prophase 1?
Oogonia enter prophase 1 of meiosis 1 by 8th month of intrauterine life (in-utero)
Does the cytoplasm divide equally in female gametogenesis?
No, cytoplasm divides unequally - 1 egg & 3 polar bodies (that apoptose - go on to die)
When is Meiosis 2 completed in female gametogenesis?
At fertilisation
What is Mendel’s Second Law?
Thelawof independent assortment states that a pair of trait segregates independently ofanotherpair during gamete formation. As the individual heredity factors assort independently, different traits get equal opportunity to occur together.
What is non-disjunction?
Failure of chromosome pairs to separate in Meiosis 1 or sister chromatids to separate properly in meiosis 2.
How can non-disjunction cause Down’s Syndrome? What are the percentages involved?
Can result in downs syndrome (non-disjunction at chromosome 21 resulting in trisomy 21) ~75% maternal meiosis I ~25% maternal meiosis II ~3-5% paternal non disjunction
How does non-disjunction cause Turner’s Syndrome?
monosomy (loss of a chromosome) - Turners syndrome, only 1 X chromosome.
What is gonadal mosaicism?
Occurs when precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis)
• One cell line is normal, the other is mutated
• Incidence increases with advancing paternal age
• Parent is healthy ( since genetic change is only in the germline so all the other cells
are unaffected - have usual genetic components), but the foetus may have genetic
diseases
• More common in males
• Can be observed with any inheritance pattern, but most commonly autosomal
dominant and X - linked
• Observed in a number of conditions, including osteogenesis imperfect and duchenne muscular dystrophy
How many arms does a chromosome have and what are their names?
2, the long arm is the q arm and the short arm is the p arm
How many chromosomes do human’s have?
46 chromosomes, 22 pairs and pair
of sex chromosomes ( XY - male & XX - female)
What is the structure of DNA?
Found in the nucleus and in mitochondria (purely maternal DNA). Arranged in a
double helix with complimentary base pairing (A-T and C-G). Half genetic material from your mother and other half from your father. In cell DNA coils around proteins
(histones) and forms nucleosomes > supercoils > chromosomes
What is the function of DNA?
DNA is a template and regulator for transcription and protein synthesis. DNA is the genetic material thus the structural basic of hereditary and genetic diseases.
In which direction does DNA polymerase read and why does this occur?
DNA polymerase reads the template strand from 3’ to 5’ thus DNA is synthesised on the daughter strand from 5’ to 3’ since DNA runs antiparallel, the daughter strand is synthesised from 5’ to 3’ since phosphate at the 5’ is used by enzyme as a source of energy for reaction to occur (ACTIVATION ENERGY)
Why is DNA replication semi-conservative?
Because each resulting DNA double helix retains one strand of the original DNA, DNA replication is said to be semi-conservative
What is the role of Topoisomerase?
Unwinds the double helix by relieving the supercoils
What is the role of DNA helicase?
Separates the DNA apart by breaking hydrogen bonds between bases, exposing nucleotides
What is the role of DNA Polymerase?
Reads 3’ to 5’ and synthesises DNA on daughter strand 5’ to 3’ (this creates DNA by working in pairs to make 2 new strands of DNA, it starts at a primer)
What is a primer?
short strand of DNA that is the start point for DNA synthesis as DNA polymerases can only add nucleotides on to an existing strand of DNA
What is the role of the Single Strand Binding Protein (SSB)
keeps two strands of DNA apart whilst synthesis of new DNA occurs - prevents annealing to form double stranded DNA
What is the role of the primase enzyme?
RNA polymerase that synthesises the short RNA primers needed to start the strand replication process
What is the role of RNAse H?
Removes the RNA primers that previously began the DNA strand synthesis
What is the first step of DNA Replication?
Prior to cell division, topoisomerase unwinds DNA and DNA helicase separates DNA apart to expose two single DNA strands and create two replication forks. DNA replication takes place simultaneously at each fork.
What is the second step of DNA Replication?
SSB’s (single-strand binding protein) coat the single DNA strands to prevent re-annealing or ‘snapping back together’
What is the third step of DNA Replication?
The primase enzyme then uses the original DNA sequence on the parent strand to synthesise a short RNA primer. Primers are necessary since DNA polymerase can only extend a nucleotide chain, not start one
What is the fourth step of DNA Replication?
DNA polymerase begins to synthesise a new DNA (via complementary base pairing using free floating nucleotides) strand by extending an RNA primer in the 5’ to 3’ direction. Each parental strand is copied by one DNA polymerase.
What is the fifth step of DNA Replication?
As replication proceeds, RNAse H recognises RNA primers bound to the DNA template and removes the primers by hydrolysing the RNA
What is the sixth step of DNA Replication?
DNA polymerase can then fill the gap left by RNAse H
What is the seventh step of DNA Replication?
DNA replication process completed when the ligase enzyme joins the short DNA pieces (Okazaki fragments) together into one continuous strand.
What is the difference between DNA and RNA?
DNA is double stranded with a complementary chain. RNA is single-stranded. Three types of RNA; mRNA (messenger), rRNA (ribosomal) and tRNA
(transfer). DNA is present in cell at all times. Many mRNA species only accumulate following cell stimulation.
What is the first step of DNA Transcription?
Topoisomerase unwinds the double helix by relieving the supercoils. DNA helicase then separates the DNA apart exposing the nucleotides. SSB’s coat the single DNA strands to prevent DNA re-annealing
What is the second step of DNA Transcription?
Free mRNA nucleotides line up next to their complementary bases on the template strand/antisense strand of DNA ( U-T & C-G).
What is the third step of DNA Transcription?
RNA polymerase (specifically RNA polymerase 2) joins the mRNA nucleotides (catalysing phosphodiester bonds between them) to form and antiparallel mRNA strand( with a 5’CAP head and a 3’Poly A tail) - starting at a promoter (specific sequence that RNA polymerase binds to - initiation of transcription. Transcription is stopped at the stop codon)
What is the fourth step of DNA Transcription?
mRNA leaves the nucleus and attaches to an 80s ribosome
What is the fifth step of DNA Transcription?
At ribosome the mRNA (bases on mRNA are read in 3 - codon) sequence is used
as a template to bind to complementary tRNA molecules at their anticodon (3
bases complementary to codon on mRNA). Ribosome reads mRNA codon by codon,
one codon will code for a particular amino acid. This amino acid is brought by a specific tRNA molecule (carried on it 3’ end) since tRNA molecules are attached to specific amino acids. BASES ARE READ 5’ TO 3’
What is the sixth step of DNA Transcription?
Enzymes remove amino acid from tRNA and amino acids are linked together by a peptide bond (created by a condensation reaction), creating a polypeptide chain - a protein
What is the stop codon?
AUG
What are the three start codons?
UGA, UAG, and UAA
What process takes a gene from primary to mature?
Splicing to remove the non-coding introns
What makes the genetic code degenerate?
Many amino acids specified by more than one codon, but each codon specifies only one amino acid
Name three factors turning off expression?
- Activation of repressors (inhibitors of RNA polymerase binding)
- Enzymes no longer activated
- Transcription and processing proteins required for RNA transcription and or processing are no longer produced
Name the 9 types of DNA mutation
- Deletion
- Duplication
- Mutations of regulatory sequence
- DNA Damage
- DNA Repair Issues
- Mis-sense mutation
- Non-sense mutation
- Splice Site mutation
- Expansion of a tri-nucleotide repeat
What is a deletion mutation?
- Can be out of frame deletion which clearly disrupts the protein e.g. deletion causing the absence of dystrophin in duchenne muscular dystrophy. If C is lost, the sequence shifts to the right once meaning the reading frame of the gene is changed. Can cause quite catastrophic effects -early mortality
- Can be an in frame deletion - whereby a complete
codon is removed thus only one amino acid is lost. This
is less catastrophic. Known as in frame deletion since
the reading frame is not altered. Results is a milder
disease - later onset death typically
What is a duplication mutation?
Duplications of genes or part of a gene (of a single base or whole gene)
What is a mutation of regulatory sequence?
coding sequence still intact ,but gene itself is switched on or off
What causes DNA damage?
chemicals, UV and radiation
What are DNA repair issues?
Base or nucleotide excision, mismatch repair or transcription-coupled repair
What is a mis-sense mutation?
A point mutation in which a single nucleotide change results in a codon that codes for a different amino acid (substitution). This can have a varied affect and can result in a silent mutation and a non functional protein E.g Sickle cell disease where CAG was replaced with CTG. May or may not be pathogenic could be a polymorphism or of no functional significance
What is a non-sense mutation?
Point mutation that produces a stop codon - results in an incomplete, usually non-functional protein. E.g. Duchenne’s muscular dystrophy
What is a splice-site mutation?
- Affects the accurate removal of an intron
- Enzyme recognises CGAT as cutting site, A changes to C and then enzyme no longer recognises the sequence so excision does not occur thus sequence of intron is translated and proteins are synthesised.
What is expansion of a tri-nucleotide repeat?
- Huntington’s disease : CAG
- Triple repeat is repeated several times in the first part of the coding sequence
- The normal range of repeats is 15-20
- If the repeats are larger than 36, the patient will develop Huntington’s, if repeats
number is larger than 36 then onset of disease will be earlier. If repeats are less
than 36 than no disease
What is anticipation?
- Anticipation: in diseases such as Huntington’s, repeats get bigger when they are transmitted to the next generation resulting in earlier symptoms of greater severity
What is a karyotype?
number and appearance of chromosomes in a cell. Spreads are arranged in size order, biggest is pair 1 and smallest is pair 22, sex pair is pair 23
Define autosomal
Chromosomes 1-22, all chromosomes except the sex chromosomes(XY)
Define Locus
The position of a gene/DNA on the genetic map
Define Genotype
Genetic constitution of an individual
Define Phenotype
Appearance of an individual which results form the interaction of the environment and the genotype
Define Allele
One of several alternative forms of a gene at a specific locus;Normal allele is also referred as wild type
Disease allele carries the pathogenic mutation
Define Polymorphism
frequent hereditary variations at a locus. Doesn’t cause problems (thats mutations). Polymorphisms can be you more/less efficient or make you more/less susceptible to disease.
Define Consanguinity
reproductive union between two relatives
Define Homozygous
Both alleles are the same at a locus
Define Heterozygous
alleles at a locus are different
Define Hemizygous
Describes genes that are carried on an unpaired chromosome. Refers to a locus on an X chromosome in a male
Define Penetrance
Proportion of people with a gene/genotype who show the expected Phenotype
Complete: gene or genes for the trait are expressed in all the population
Incomplete: the genetic trait is only expressed in parts of the population
Define Variable Expression
Variation in clinical features (type and severity) of a genetic disorder between individuals with the same gene alteration
Define Sex Limitation
Expression of a particular characteristic limited to one of the sexes (BRCA gene)
Define Multifactorial Condition
Diseases due to a combination of genetic and
environmental factors. If the condition is more common in one particular sex, the relatives of an affected individual of the less frequently affected sex will be a higher risk than relatives of an affected individual or the more frequently affected sex i.e if a boy has the condition then female relatives are more at risk and vice versa.
Define Late-Onset
Condition not manifested at birth (where it does this is called
congenital). Classically adult-onset e.g Huntington’s
Define Autosomal Dominant (Mendelian)
A disease that only manifests in theheterozygous state.
• Affects both males and females in equal proportions.
• Affected
• individuals in multiple generations.
• Transmission by individuals of both sexes to
• both sexes.
• NOTE: sometimes both parents are unaffected, this can be for three
• reasons: most commonly they don’t have the genes for it, gonadal mosaicism or
• SOMETIMES the mother has REDUCED PENETRANCE or VARIABLE
• EXPRESSION i.e. disease is there but not expressed clearly. Only one defective
• gene needed. 50% chance of offspring having condition (1 affected and 1 unaffectedparent). Example. Huntington’s disease.
• ONLY WAY TO PASS ON DISEASE FROM MALE TO MALE. Thus if you see male-male transmission, MUST BE AUTOSOMAL DOMINANCE INHERITANCE
Define Autosomal Recessive (Mendelian)
A disease that manifests in the homozygous state.
Two defective genes required.
CARRIER PARENTS: 25% chance of offspring
(from 2 carrier parents) have condition. 50% chance of offspring being a carrier.
Calculations at conception. Healthy siblings have a 2/3 chance of being carriers.
Male and females affected in equal proportions. Affected individuals only in a singlegeneration.
Parents can be related e.g consanguineous (recessive disorders most
common in these types of family) Example. CYSTIC FIBROSIS:
- Most common autosomal recessive condition affecting whites in UK
- Chronic condition affecting mainly the lungs and gut, variable presentation
- Incidence of 1 in 25,000
- Population carrier frequency for cystic fibrosis is 1/25 (i.e 25% of the population
is a carrier) - NOTE, YOU ARE A 50% CHANCE OF CARRIER IF BOTH PARENTS
ARE CARRIERS
- NOTE: when looking at probabilities to see risk of being carriers etc. the already
AFFECTED CHILD is disregarded, so if you get one unaffected, 2 carriers and one
affected, the probability of being a carrier is NOT 1/2 since affected child is
disregarded, instead it is a 2/3
Define X-Linked(Sex-linked) Inheritance (Mendelian)
Caused by a mutation in genes on the X-chromosome. e.g. haemophilia and duchenne muscular dystrophy
• Males XY and Females XX.
• X-linked can never be passed from father to son (NO MALE-TO-MALE
TRANSMISSION - BECAUSE SONS ALWAYS GET THEIR X CHROMOSOME FROM
THEIR MOTHER) - all sons from affected male and unaffected female are unaffected.
• All daughters from an affected male are CARRIERS all sons are UNAFFECTED
• Males can NEVER be carriers
• Usually only males are affected
• Transmitted (usually) through unaffected females
• X-linked dominant example is Alport’s syndrome (kidneys)
• X-linked recessive example is Duchenne’s muscular dystrophy
Define Lyonisation
The process of X chromosome inactivation
• One of the two X chromosomes in every cell in a female is randomly inactivated early
in embryonic development.
• X chromosome inactivated to prevent female cels having twice as many gene
products from the X chromosome as males
• Only one functional copy of X chromosome
Define Barrbody
Inactive X chromosome since packaged in heterochromatin (cannot be transcripted)
Define Imprinting (non-mendelian)
For some genes only 1 out of the 2 alleles is
active, the other is inactive. For particular genes it is always the paternal or the maternal allele
Define Dominant Negative Effect
Dominant negative mutations (also calledantimorphicmutations) have an altered gene product that acts antagonistically to the wild-type allele. These mutations usually result in an altered molecular function (often inactive) and are characterized by a dominant orsemi-dominantphenotype.
Name the mendelian classifications of disease?
autosomal dominant/ recessive or X-linked
Name the non-traditional classifications of diseases?
Mitochondrial (ALL MITOCHONDRIA IS INHERITED FROM MOTHER -thus men cannot pass onmitochondrial mutations), imprinting, mosaicism
What are the values for dietary energy sources?
Lipids- 9kcal/g
Alcohol-7kcal/g
Protein- 4kcal/g
Carbohydrate- 4kcal/g
Define metabolism?
Metabolism refers to the sum of the chemical reactions that take place within each cell of a living organism
Define Basal Metabolic Rate?
amount of energy needed to keep the body alive in the rest state. It is the energy needed to keep the heart pumping, the brain working and the liver and kidneys functioning - BMR = 1kcal/kg body mass/hr (24kcal/kg/day), an adult requires approximately 0.8g/kg ideal body weight protein per day
Factors increasing BMR
High BMI
Hyperthyroidism
Low ambient temperature
Fever/infection
Pregnancy (due to increase in weight and thyroid hormone)
Exercise
Factors decreasing BMR
Age (as you age, BMR decreases)
Hypothyroidism
Starvation
Gender (females have lower BMR since they have less metabolically active tissues
Decreased muscle mass
Conditions for measuring BMR
• Lying still at physical and mental rest
• Thermo-neutral environment (27 – 29oC)
• No tea/coffee/nicotine/alcohol in previous 12 hours
• No heavy physical activity previous day
• Establish steady-state (~ 30 minutes)
* If any of the above conditions are not met, we may refer to Resting Energy Expenditure (REE) or Resting Metabolic rate (RMR)
What is the Daily Energy Expenditure (DEE)
- Daily energy expenditure (DEE) - Energy to support our BMR and our physical
activity + energy required to process food we eat (diet induced thermogenesis)
What are the values for storage of excess energy?
Triglycerides (excess lipid)-Approx 15kg
Glycogen (excess glucose)- Approx 200g in liver and 150g in muscle
Protein- Approx 6kg
What are anabolic and catabolic?
Anabolic – synthesise larger molecules from smaller components
Catabolic – break down larger into smaller
What are the pathways of dietary component metabolism? And are they catabolic or anabolic?
Biosynthetic anabolic
Fuel Storage Anabolic
Oxidative Catabolic
Waste Disposal Either
What is the process for fatty acid activation in the cytoplasm?
Fatty acid + ATP + CoA > Acyl-CoA + PPi (pyrophosphate) + AMP. The adenosine is
taken from ATP and used to make the Acyl-Coenzyme A (Acyl-CoA).
What is the second step of fatty acid beta oxidation?
Oxidation of fatty acids occurs in the mitochondria, however most fatty acids (that
are over 12 carbons long) cannot get through the outer-mitochondrial membrane on their own. In order to get through, the Acyl CoA must be converted: Acyl CoA > (enzyme Carnitine acyltransferase 1 (resides in the outer mitochondrial membrane))> Acyl Carnitine. In this process the Coenzyme A is removed from Acyl CoA and is recycled, as you can see, the molecule Carnitine is added. The Acyl Carnitine can then be transported into the mitochondria through the outer mitochondrial membrane.
What is the third step of fatty acid beta oxidation?
Once inside the mitochondria another enzyme Carnitine acyltransferase 2 converts Acyl carnitine back to Acyl CoA : Acyl Carnitine > (enzyme Carnitine acyltransferase 2) > Acyl CoA. In this process a Coenzyme A is re-added and the carnitine ripped off to regenerate Acyl CoA. The carnitine can then diffuse through the outer mitochondrial membrane to be used again to covert Acyl CoA to Acyl Carnitine (THIS IS KNOWN AS THE CARNITINE SHUTTLE)
What is the final step of fatty acid beta oxidation?
Now the fatty Acyl CoA can be oxidised. It is termed beta-oxidation (b-oxidation) since it occurs through the sequential removal of 2-carbon units by oxidation at the beta-carbon position of the fatty Acyl-CoA molecule. Each round of b-oxidation produces 1 mol of NADH, 1 mol of FADH2 & 1 mol of Acetyl CoA.
• The Acetyl CoA can then be used in the Kreb’s cycle (above)
• The NADH & FADH2 produced from the beta-oxidation and from the Kreb’s cycle
can then be used in oxidative phosphorylation
How many moles of ATP are produced with oxidation of one mole of Oleic Acid (18 C fatty acid)?
The net result of the oxidation of one mole of oleic acid (an 18-carbon fatty acid) will be 146 moles of ATP as compared to 38 moles of ATP produced from
1 mol of glucose
Can fatty acids pass through the blood-brain barrier?
No
What happens when acetyl coA supplies outweight the demand from the Kreb’s cycle?
one result is the synthesis of ketone
bodies - known as ketogenesis
Where are ketone bodies synthesised?
Ketone bodies (acetone, acetoacetate &
B-hydroxybutyrate) are synthesised in the
mitochondrial matrix from Acetyl CoA
generated from b-oxidation
What is the function of thiolase?
Converts 2 Acetyl coA to acetoacetyl coA
What is the function of HMG coA Synthase?
Converts acetoacetyl coA to 3-hydroxy-3-methyl glutaryl coA (HMG coA)
What is the function of HMG coA Lisase?
Converts HMG coA to Acetoacetate
What is the function of D- beta-hydroxybutyrate dehydrogenase?
Converts Acetoacetate to D-beta-Hydroxybutyrate
What can be spontanteously be formed from acetoacetate?
Acetone
What happens when carbohydrate utilisation is low or deficient?
when carbohydrate utilisation is low or deficient, the level of oxaloacetate will also be low resulting in a reduced flux through the Kreb’s cycle - leading to an increased release of ketone bodies from the liver to be used as fuel by other tissues
What is the function of Succinyl coA- acetoacetate coA transferase and in what organ is the supply low?
Acetoacetate can then be activated to Acetoacetyl CoA, the supply of this enzyme is low in the liver thus preventing ketone breakdown in the liver
What is the process of diabetic ketoacidosis?
Reduced supply of glucose (since there will be a significant decline in circulating insulin) and an increase in fatty acid oxidation (due to an increase in circulating glucagon)
The increased production of Acetyl-CoA leads to ketone body production that exceeds the ability of peripheral tissues to oxidise them.
Ketone bodies are relatively strong acids (pH 3.5), and their increase lowers the pH of blood.
This acidification of the blood can have many consequences but most critical is the fact that it IMPAIRS THE ABILITY OF HAEMOGLOBIN TO BIND TO OXYGEN - note if a patient is in diabetic ketoacidosis, the excess ketones in the blood will result in their BREATH SMELLING OF PEAR DROPS (KETONES).
What is the structure and function of the nucleus?
Structure: Double nuclear membrane
• Euchromatin-lighter areas
• Nucleolus
• Heterochromatin-darker areas
Function:
Brain of the cell
Houses DNA in the form of chromatin within the nucleolus (site of ribosomal RNA formation i.e. DNA transcription
What is the structure and function of the nucleolus?
Structure:
• 1-3 microns in diameter
• Seen using light microscope
• Contain both euchromatin and heterochromatin
• Three regions of the nucleolus can be distinguished by electron microscopy
Function:
Site of ribosomal RNA formation
• Pars amorpha(pale areas)- nuclear organiser regions with specific RNA-binding proteins, correspond to large loops of transcribing DNA containing the ribosomal RNA genes
• Pars fibrosa(dense-staining regions- correspond to transcripts of ribosomal RNA genes beginning to form ribosomes
• Pars granulosa (granular regions)- correspond to RNA-containing maturing ribosomal subunit particles
What is the structure and function of the mitochondria?
Structure:
Double membrane, inner membrane is highly folded
Function:
Site of oxidative phosphorylation
Outer membrane: lipid synthesis and fatty acid metabolism
Inner membrane: respiratory chain (electron transport) ATP production
Matrix: Kreb’s cycle
What is the structure and the function of the RER?
Structure:
Highly folded flattened membrane sheets
Function:
Site of protein synthesis
What is the structure and function of the SER?
Structure:
Highly folded flattened membrane sheets
The lipid synthetic enzymes are located on its outer(cytosolic) face with ready access to lipid precursors
Once synthesised and incorporated into the outer part of the SER membrane lipid bilayer, phospholipids are flipped over into the inner part by specific transport proteins colloquially called flipases
Function:
Site of membrane lipid synthesis
Processes and stores synthesised proteins
In addition to its functions in biosynthesis the ER has two other important roles:
• Detoxification or activation of foreign compounds, including some drugs, by ER proteins termed cytochrome P-450 proteins
• Storage of intracellular calcium
What is the structure and function of the golgi apparatus?
Structure: Parallel stacks of membrane
Located close to nucleus
Can’t be seen in most cells but prominent in plasma cells (why?)
• Hard to see on light microscopes
• Particularly prominent in plasma cells-seen as a perinuclear hoff, pale area next to nucleus
Function:
Cis (first) golgi (nuclear facing)- receives SER vesicles, protein phosphorylation occurs here
Medial golgi- Modifies products by adding sugars- forms complex oligosaccharides by adding sugars to lipids and peptides
Trans golgi network- proteolysis of peptides into active forms and sorting of molecules into vesicles which bud from the surface
What is the structure and function of vesicles?
Structure:
very small spherical membrane-bound organelles
Function:
transport and store material and exchange cell membrane between compartments
Many types: cell surface derived (pinocytotic and phagocytotic vesicles), golgi-derived transport vesicles, ER-derived transport vesicles, lysosomes and peroxisomes
What is the structure and function of lysosomes?
Structure:
Contain digestive enzymes
Lysosomes are formed by fusion of 2 hydrolase vesicles and endosomes which produces an endolysosome which lowers pH and enzyme that degrades proteins at that pH
Function:
waste disposal system and is the site of breakdown for most molecules, derived from golgi, H+-ATPase on membrane creates low pH to enable acid hydrolases to function. They also breakdown debris from dead cells and bacteria and damaged cell organelles
What is the structure and function of peroxisomes?
Structure:
small membrane-bound organelles containing enzymes which oxidise long chain fatty acids (long chain FAD- amino oxidase, catalase, and urate oxidase)
Small 0.5-1 micron
Function:
Involved in fatty acid beta oxidation.
They also produce hydrogen peroxide (by product of the breakdown of fatty acids) which can be use to destroy pathogens. But peroxisomes can destroy hydrogen peroxide thereby preventing its toxic effects and protecting the body etc
What is the structure and function of cytoskeleton?
Structure:
Filamentous proteins which brace the internal structure of the cell-helps cells maintain their shape and internal organisation
Not visible in light microscopy
Function:
Microfilaments (5nm)- actin forms a bracing mesh (cell cortex) on the inner surface of the cell membrane
Intermediate filaments (10nm and 6 types of protein)- anchored transmembrane proteins which can spread tensile force through tissues. Specific functions unknown
6 proteins:
Cytokeratins-epithelial cells (found in mant different cells)
Desmin- Myocytes
Glial fibrillary acidic protein (supports neurones in the brain)- astrocytic glial cells
Neurofilament protein-neurons
Nuclear lamina- nuclei of all cells
Vimentin-mesodermal cells
Microtubules (25nm)- Tubulin (alpha and beta, which arrange in groups of 13 to form hollow tubes). Arise from centrosome. Found in all cells except for erythrocytes
What are the storage products and inclusions?
Lipofuscin-membrane bound orange-brown pigment, peroxidations of lipids (degradation of lipids) in older cells, common in heart and liver, sign of wear and tear
Lipid-Non-membrane-bound vacuoles, appears as empty space in histology since dissolved in processing, stored in adipocytes and liver
Glycogen- CHO polymer in cytoplasm, normally only seen on electron microscopy, may accumulate in some cells and in some diseases
What are the four structures in the cell membrane and what are the functions of each?
Glycolipid:Communication and joins cells to form tissues+stability
Glycoprotein: Cell to Cell recognition and can act as a receptor
Cholesterol: Maintains fluidity of the membrane
Intrinsic Protein:
What are the 10 functions of the cell membrane?
- Communication
- Anchoring
- Occluding
- Insulation
- Adhesion
- Responding to signals
- Barrier to the outside environment (compartmentalise cells)
- Selective barrier for passage of molecules
- Transports molecules in and out
- Specific enzymatic activity
What is the process of endocytosis?
Energetic process to absorb/engulf molecules into a cell. Some extracellular fluid is
usually engulfed too along with the molecule etc. - a portion of the membrane is
invaginated to form a membrane bound vesicle called an endosome
• Occurs in neutrophils & macrophages - they implement phagocytosis (eating)
whereby they engulf entire cells/macromolecules to form a phagosome
• Pinocytosis (drinking) - bringing in dissolved solutes
• Receptor mediated - specific, found in depressed areas (coated pits) - allows the cell
to get the molecules it needs. Ligands bind to receptor, this complex is engulfed -
releasing the ligand into the cytosol (fluid portion of the cytoplasm outside the cell
organelles)
What is the process of exocytosis?
Vesicle from the golgi apparatus, fuse with the plasma cell membrane, resulting in the
expulsion of waste or the secretion of enzyme/hormones
What is the cell membrane freely permeable to and impermeable to?
Freely permeable: Water via aquaporins
Gases (CO2, N2, O2)
Small Uncharged Polar molecules (Urea, Ethanol)
Impermeable:
Ions
Charged polar molecules (ATP, Glucose-6-phosphate
Large uncharged polar molecules (Glucose)
What are the features of channels?
Narrow Aqueous Pore
Selective for size and charge
Passive
May be gated (voltage or ligand)
Usually ions (e.g. Na+, K+) or water (aquaporins)
What are the features of carriers?
Specific binding site
Carrier undergoes a conformational change
Different types:
Uniport- single substance
Symport-two substances in the same direction
Antiport- two substances in the opposite direction
Active (pumps) or passive
What are the three main forces that drive substances into a cell?
Chemical, Electrical, Electrochemical
What are the features of a chemical drive?
Based on concentration differences across the membrane
All substances have a concentration gradient
Force directly proportional to the concentration gradient
What are the features of an electrical drive?
Also known as membrane potential
Based on the distribution of charges across the membrane
Only charged substances e.g. Na+, K+
Force depends on size of membrane potential and charge of ion
What are the features of an electrochemical drive?
Combines the chemical and electrical forces
Net direction is equal to the sum of chemical and electrical forces
Only charged substances e.g. Na+, K+
What are the four types of membrane transport?
- Simple Diffusion
- Facilitated Diffusion
- Primary Active Transport
- Secondary Active Transport
Describe facilitated diffusion? Is it passive or active?
the movement of solutes from a region of their high
concentration to a region of their low concentration through protein channels (WITHOUT CARRIER PROTEINS). This continues until dynamic equilibrium is
reached. e.g. Glucose - protein assisted which is regulated by insulin. Voltage gate channels activated by action potentials
Passive
Describe primary active transport?
the movement of solutes from a region of low concentration to a region of high concentration against the concentration gradient. Both transmembrane carrier protein and ATP is required. e.g Na/K ATPase pump -going against chemical and electrical gradients
Describe secondary active transport?
the movement of solutes from a region of low concentration to a region of high concentration against the concentration gradient. Both transmembrane carrier protein and ATP is required. e.g Na/K ATPase pump -going against chemical and electrical gradients
What is an example of facilitated diffusion and an example of when it goes wrong?
Example:
• GLUT4 carrier protein:
• Expressed in skeletal muscle and adipose tissue
• Glucose uptake by facilitated diffusion
• Expression upregulated by insulin
when it goes wrong: • GLUT1 present in many cells, including the brain, where it transports glucose across the blood-brain barrier via facilitative diffusion • GLUT1 Deficiency Syndrome: • Very rare disorder • Mutations in gene that encodes GLUT1 • Less functional GLUT1 - reduces the amount of glucose available to brain cells • Symptoms include seizures, microcephaly, developmental delay
What is an example of primary active transport and an example of when it goes wrong?
- Common example is Na+/K+-ATPase:
- Pumps 3 Na+ out of the cell, 2 K+ into the cell
- Utilises the hydrolysis of ATP to ADP + Pi
When it goes wrong:
When it goes wrong:
• ATP7B protein is a Cu2+-ATPase present in the liver that transports copper into bile
• Wilson’s disease
• Rare disorder
• Mutations in ATP7B gene
• Results in deposition of copper in the liver and other tissues e.g. brain, eyes
• Symptoms include liver disease, tremor,
Kayser-Fleischer rings,
What is an example of secondary active transport and an example of when it goes wrong?
• Example is the Na+/glucose
cotransporter proteins (SGLT):
• Present in intestinal lumen
and renal tubules
• Transports glucose from low
to high concentration
• Na+/K+-ATPase generates a
sodium gradient to enable
co-transport of sodium and
glucose
When it goes wrong:
• SGLT1 transports glucose and galactose from the intestinal lumen
• Glucose-Galactose Malabsorption:
• Very rare disorder
• Mutations in SGLT1
• Less functional SGLT1 -
inability to transport
glucose and galactose,
resulting in their
malabsorption
• Symptoms include
severe, chronic diarrhoea,
dehydration, failure to thriveWhat are the four types of membrane proteins? What are their intracellular effects? What is an example of each?
Ligand-gated ion channels-Influx of ions leads to changes in membrane potential or ionic concentration within cell (Cholinergic nicotinic receptors)
G protein-coupled receptors-Protein phosphorylation (Alpha and beta adrenoreceptors)
Enzyme-linked receptors-Protein and receptor phosphorylation (Insulin receptors)
Intracellular Receptors-Protein phosphorylation and altered gene expression (Steroid receptors)
What is the definition of homeostasis?
the maintenance of a constant internal environment
• Homeostasis is the property of a system in which variables are regulated so that
internal conditions remain stable and relatively constant
• Examples: temperature, blood pressure, pH, glucose and oxygen concentration
What are the four types of communication involved in homeostasis?
- Autocrine
- Paracrine
- Endocrine
- Exocrine
What is the action of autocrine communication?
Chemical is released from cell into the
extracellular fluid and then acts upon the very cell that
secreted it
What is the action of paracrine communication?
Chemical messengers involved in the
communication between cells, released into extracellular fluid - travel short distances, local communication. E.g Acetylcholine at neuromuscular junction
What is the action of endocrine communication?
(secretion into blood): Produce and secrete
hormones, communication between cells, travel much
longer distance, systemic communication, can affect thewhole body.
Organs involved: hypothalamus
(hypothalamic hormones include dopamine) and
pituitary (anterior pituitary hormones include FSH,
LH and thyroid stimulating hormone (TSH), posterior
pituitary hormones include oxytocin (released during
child birth) and ADH/ vasopressin) (in brain, master
endocrine organs), thyroid (front of neck),
parathyroid (directly behind neck), adrenals (above
kidneys), pancreas, ovaries and testes
What is the action of exocrine communication?
Secretion into ducts then into organ
What is the key difference between endocrine and paracrine?
Hormones travel in blood in endocrine whereas in paracrine chemical messengers only travel in extracellular fluid.
Endocrine affects more things and travels further than paracrine
Define positive feedback and negative feedback?
Positive feedback loop: amplification of signal. E.g. clotting cascade & oxytocin release during childbirth
Negative feedback loop: centre of homeostasis, main way endocrine hormones
are controlled.
Define hormone?
Molecule that acts as a chemical messenger
What are the types of hormones?
Peptide, Steroid, Amino acid
What is the structure, action, and an example of a peptide hormone?
Made from short chain amino acids, vary in size from few amino acids to small proteins, some have carbohydrate side chains (glycoproteins), they are large,hydrophilic charged molecules that cannot diffuse across a membrane.
bind to receptors on membranes. Peptide hormone is pre-made and stored in cell, then released and dissolved into blood when needed. Binds to receptor on membrane then chemical reaction produces a quick response from the cell and a 2nd messenger is released in the cell - VERY FAST (minutes) (signal transduction cascade).
Insulin, growth
hormone, thyroid stimulating hormone (TSH)
and ADH/vasopressin
What is the structure, action, and an example of a steroid hormone?
Synthesised from cholesterol
Water insoluble & lipid soluble
can crossmembranes BUT requires transport
proteins in blood, targets an intracellular
receptor. Steroid hormone is made by cell and diffuses out once made (not stored), SLOW RESPONSE (hours/days) since it directly
affects DNA.
Testosterone, oestrogen and cortisol (long term stress
hormone)
What is the structure, action, and an example of an amino acid hormone?
Synthesised from tyrosine
acts in same way to peptide
adrenaline, thyroid hormones (thyroxine (T4) and triiodothyronine (T3))
Define osmosis?
net movement of solvent molecules through a semipermeable membrane to a higher solute concentration (i.e. lower water conc.)
Define osmolality?
measure of the number of dissolved particles per kg of fluid
Define osmolarity?
measure of the number of dissolved particles per L of fluid
Define osmotic pressure?
pressure applied to a solution, by a pure solvent, required to prevent inward osmosis, through a semipermeable membrane
Define oncotic pressure?
form of osmotic pressure exerted by protein that tends to pull fluid into its solution - water moves from interstitial fluid into plasma
Define hydrostastic pressure?
Pressure difference between capillary blood(plasma) and interstitial fluid- water and solutes move from plasma into interstitial fluid
What are the volumes within the ICF and ECF?
ECF:
14L (20% of body weight)
ICF:
28L (40% of body weight)
ECF breakdown:
Interstitial fluid: 10L
Plasma: 3L
Transcellular 1L
28L ICF
What are the regulating hormones of water levels?
ADH, Aldosterone & Atrial natriuretic peptide
What are components of water intake?
Drink, diet & IV fluid
What are components of water loss?
Water loss: Kidneys
Insensible losses: sweat, breath, vomiting & faeces
What happens when water is lost from the ECF?
increase in solutes or decrease in water = increase in osmolality in ECF
Change detected by osmoreceptors in the hypothalamus
- Results in ADH/vasopressin release from posterior pituitary
- ADH acts to increase water reabsorption in the collecting ducts of the kidney in
order to dilute the solute and return water in ECF to normal
• What happens when there is decreased renal blood flow:
- decrease in water in ECF = decrease in effective circulating volume = decrease in
renal blood flow
- Results in the release of renin from the juxtaglomerular kidney cells in the kidneys
- Renin converts angiotensinogen to angiotensin I, angiotensin converting enzyme (ACE) then
converts angiotensin I into angiotensin II, which in turn triggers the release of aldosterone from the adrenal cortex above the kidneys
- Angiotensin II and Aldosterone increase Na+ reabsorption in the kidneys in exchange for potassium or hydrogen excretion
- Also stimulate ADH release
- Sodium reabsorption brings water with it to return water in ECF to normal
• Osmolality (sodium) is controlled by changing water. Water is controlled by changing osmolality (sodium)
What are causes and consequences of dehydration?
Causes of dehydration: water deprivation, vomiting, diarrhoea, burns, heavy
sweating, diabetes insipidus (literally pee bucket loads since too little ADH
produced), diabetes mellitus & drugs
• Consequences of dehydration: thirst, dry mouth, inelastic skin, sunken eyes, raised
haematocrit (viscosity of blood), weight loss, confusion & hypotension
What are causes of excess water intake?
High intake/ decreased loss of water, excess ADH
What are the causes and consequences of hyponatraemia?
Causes:
Water excess,
diuresis (increase urine rate), Addison’s
disease, excess IV fluids & oedema
Consequences:
Intracellular over hydration -
hypotension since H2O goes intracellular as solute concentration increases -
Osmosis
Headaches, confusion, convulsions, and serous effusion (excess water in a body cavity)
What are the causes and consequences of hypernatraemia?
Causes:
renal failure, mineralocorticoid excess
(sodium excess), osmotic diuresis (increased urine rate due to high amount of water)
and diabetes insipidus
Consequences:
cerebral intracellular dehydration - high
sodium = low H2O which then dehydrates the brain as there is a lower water
concentration since H2O leaves intracellular to go extracellular as solute
concentration increases - osmosis
What are the causes and consequences of hypokalaemia?
Causes:
diarrhoea, vomiting, alkalosis,
hypomagnesaemia (low magnesium levels).
Consequences:
weakness & cardiac
dysrhythmia (abnormal heart beat - again since K is necessary for resting potentials
and thus action potential generation etc.)
What are the causes and consequences of hyperkalaemia?
Causes:
renal failure, diuretics/ACE inhibitors,
Addison’s, Acidosis
Consequences:
Risk of myocardial infarction since high
potassium levels mess with resting potential generated in heart for heart contraction
What are the causes and consequences of hypocalcaemia?
Causes:
Vitamin D deficiency, magnesium deficiency,
renal disease, parathyroidectomy (no parathyroid hormone released) & intestinal
malabsorption.
Consequences:
tetany (spasms of the hands, feet & voice box)
What are the causes of consequences of hypercalcaemia?
Causes:
primary hyperparathyroidism (parathyroid
gland producing too much parathyroid hormone meaning calcium is leached from
bone to increase blood calcium levels), skeletal metastases, vitamin D toxicity and
tuberculosis.
Consequences:
metastatic calcification (deposition of calcium salts in
otherwise normal tissues - resulting in stones) and kidney stones (renal calculi)
What are the four types of oedema and what are their processes?
Lymphatic: Obstruction of the lymphatic drainage by a tumour/parasite
Hypoalbuminaemic: Reduced oncotic pressure due to low albumin in the plasma therefore fluid collects in the interstitium
Venous: Due to increased venous pressure or venous obstruction, there is increased end pressure and it is therefore more difficult for fluid to move back into the ECF
Inflammatory: proteins leak out due to increased vascular permeability-they bring in water, thereby diluting the toxins - fibrinogen polymerises to form a
fibrin mesh and immunoglobulins collect
What are the properties of primary protein structure?
Linear sequence of amino acid
Held together by covalent bonds
What are the properties of secondary protein structure?
Formation of either alpha helix (H-bonds between each carbonyl group and the H attached to the N which is 4 amino acids along the chain, side chain looks outwards) or beta pleated sheets (formed by H bonds between linear regions of polypeptide chains, chains from 2 proteins or same protein, if the chain is folding back, structure is usually a 4 amino acid turn- called a hairpin loop or beta turn) due to hydrogen bonds between amino acids- determined by the local interactions between the side chains and sequence of amino acids
Super secondary structure refers to a combination of secondary structures. Structures and functional units of folded proteins often consist of combinations of alpha and beta structures
What are the properties of tertiary protein structure?
Overall 3D confirmation of a protein. Bonding involved is electrostatic, H-bonds and covalent bonds. Folding of the secondary structure into a globular structure due to bonds such as ionic bonds, disulphide bridges and Van der Waals forces. Confirmation can change with temperature or pH
What are the properties of quaternary protein structure?
3D structure of protein composed of multiple sub-units. Same non-covalent interactions as tertiary structures. 2 or more tertiary structures joined together to form a protein
What forces are present in proteins?
Van Der Waals Covalent Bonding Hydrogen Bonds Ionic Bonding Hydrophobic bonding Disulphide bonding
Define enzymes?
Enzymes provide an alternative reaction pathway with a lower activation energy
• Enzymes are proteins that work as catalysts, enable reactions to occurs that
otherwise would not be able to occur at physiological (body) temperatures and
conditions
• Enzymes bind the reactants (substrates) and convert them to products, they then
release the products and return to their original form.
How can enzymes be regulated?
Enzymes can be regulated by altering the concentration of substrates, products, inhibitors or activators, they can also be regulated by
modifying the enzyme itself by phosphorylation.
What are oxidation-reduction coenzymes?
involved in reactions where electrons are transferred from one compound to the other. E.g. NAD + transfers electrons with hydrogen and is important in energy processes including the generation of ATP.
What are activation-transfer coenzymes?
form a covalent bond and are regenerated at the end of the reaction
What are co-enzymes?
they cannot in themself catalyse a reaction but can help enzymes to do so. They can bind with the enzyme protein molecule to form the active enzyme
What is an isoenzyme?
enzymes that have a different structure and sequence but catalyse the same reaction
How does ATP provide energy?
When the phosphate bonds are broken energy is released BUT to ‘break’ bonds an input of energy
is required. As bonds reform in the products of the reaction of the hydrolysis of ATP energy is
released. The energy released making the new bonds is greater than the energy required to
hydrolyse the bonds (since they are relatively weak) thus meaning the hydrolysis of ATP gives out
energy
What are the methods for generating ATP?
Glycolysis
- Kreb’s cycle
- Oxidative phosphorylation
- Substrate level phosphorylation
- Electron transport chain
- Beta oxidation
What is the summary equation for glycolysis?
1 glucose + 2ADP + 2 NAD+ > 2x pyruvate + 4 x ATP + 2NADH + 2H+ + 2H20
SIMPLIFIED: Glucose + 2ADP + 2Pi + 2NAD+ > 2 Pyruvate + 2ATP + 2NADH + 2H+ + 2H20
What is a kinase enzyme?
enzyme that adds/removes phosphate group to things from an ATP
What is an isomerase enzyme?
enzyme that rearranges structure of substrate without changing the molecular formula. (Similar to a mutase)
What is an aldolase enzyme?
enzyme that creates or breaks carbon-carbon bonds
What is an dehydrogenase enzyme?
enzyme that moves hydride ion (H-) to an electron acceptor e.g. (NAD+ of FAD+)
What is an enolase enzyme?
enzyme that produces a carbon=carbon double bond by removing a hydroxyl group (OH)
What is step 1 of glycolysis, what is the enzyme and what goes in and out?
Process: Glucose to glucose-6-phosphate
Enzyme: Hexokinase
IN: ATP
OUT: ADP
What is step 2 of glycolysis, what is the enzyme and what goes in and out?
Process: Glucose-6-phosphate to fructose-6-phosphate
Enzyme: Phosphohexose Isomerase
IN: Nothing
OUT: Nothing
What is step 3 of glycolysis, what is the enzyme and what goes in and out?
Process: Fructose-6-phosphate to Fructose 1, 6 Bisphosphate
Enzyme: Phosphofructokinase-1 (rate limiting step)
IN: ATP
OUT: ADP
What is step 4 of glycolysis, what is the enzyme and what goes in and out?
Process: Fructose 1, 6, bisphosphate to 3-phosphogluceraldehyde (2x)
Enzyme: Fructose bisphosphate aldolase
IN: Nothing
OUT: Nothing
What is step 5 of glycolysis, what is the enzyme and what goes in and out?
Process:
Fructose 1, 6, bisphosphate to hydroxyacetone phosphate to 3 phosphoglyceraldehyde (2x)
Enzyme: Phosphate isomerase
IN: Nothing
OUT: Nothing
What is step 6 of glycolysis, what is the enzyme and what goes in and out?
Process: 3-phosphoglyceraldehyde (2x) to 1, 3- bisphosphoglycerate (2x)
Enzyme: Glyceraldehyde-3-phosphate dehydrogenase
IN: Pi, NAD+
OUT: 2xNADH +H+
What is step 7 of glycolysis, what is the enzyme and what goes in and out?
Process:
1,3- bisphosphoglycerate (2x) to 3-phosphoglycerate (2x)
Enzyme: Phosphoglycerate kinase
IN: ADP + Pi
OUT: 2xATP
What is step 8 of glycolysis, what is the enzyme and what goes in and out?
Process: 3-phosphoglycerate (2x) to 2-phosphoglycerage (2x)
Enzyme: Phosphoglycerate mutase
IN: Nothing
OUT: Nothing
What is step 9 of glycolysis, what is the enzyme and what goes in and out?
Process: 2-Phosphoglycerate (2x) to phosphoenolpyruvate (2x)
Enzyme: Enolase
What is step 10 of glycolysis, what is the enzyme and what goes in and out?
Process: Phosphoenolpyruvate (2x) to Pyruvate(2X)
Enzyme: Pyruvate kinase
IN: ADP + Pi
OUT: 2xATP
What happens in anaerobic conditions?
Process:
Pyruvate (2x) to Lactate
no enzyme
IN: NADH +H+
OUT: NAD+(X2)
Why is glycolysis inhibited by acidosis?
PHOSPHOFRUCTOKINASE-1 (PFK-1) IS PH DEPENDENT AND IS INHIBITED BY ACIDIC CONDITIONS
What are the regulators of glycolysis?
- Adenosine monophosphate (AMP) is an allosteric activator (modifies the active
site of the enzyme so that the affinity for the substrate increases) of phosphofructokinase-1 (PFK-1). AMP binds to PFK-1 resulting in a conformational
change - increasing affinity of PFK-1 for fructose-6-phosphate - Adenosine triphosphate (ATP) is an allosteric inhibitor (modifies the active site of
the enzyme so that the affinity for the substrate decreases) for PFK-1 - Thus at low ATP levels = fast reaction speed of PFK-1 > fructose 1,6 bisphosphate,
and at high ATP levels = slow reaction speed of PFK-1 > fructose 1,6 bisphosphate - NOTE: AMP opposes the allosteric inhibition by ATP
Where does Kreb’s Cycle take place?
In the mitochondrial matrix
What is the equation of the Kreb’s Cycle?
Acetyl CoA + 3NAD+ + FAD + GDP + ADP + Pi + 2H2O > 2CO2 + CoA + 3 NADH +3H+ + FADH2 + GTP + ATP
Why can the Kreb’s Cycle only occur in aerobic conditions?
the Kreb’s cycle can only take place in aerobic conditions since oxidative
phosphorylation is required to covert NADH & FADH2 back to NAD+ and FAD to be
used in the conversion of Isocitrate to a-Ketoglutarate and a-Ketoglutarate to Succinyl
coenzyme A & Succinate to Fumarate & Malate to Oxaloacetate
What is step 1 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Citrate(6C) to Isocitrate(6C)
Enzyme: Aconitase
IN: Nothing
OUT: Nothing
What is step 2 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Isocitrate(6C) to alpha ketoglutarate(5C)
Enzyme: Isocitrate dehydrogenase
IN: NAD+
OUT: NADH + H+
What is step 3 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Alpha ketoglutarate (5c) to succinyl coenzyme A (4C)
Enzyme: Alpha ketoglutarate dehydrogenase
IN: NAD+
OUT: CO2 + NADH + H+
What is step 4 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Succinyl coenzyme A (4C) to Succinate (4C)
Enzyme: Succinyl coenzyme A
IN: GDP +Pi +ADP
OUT: GTP +ATP
What is step 5 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Succinate (4C) to Fumarate (4C)
Enzyme: Succinate dehydrogenase
IN: FAD
OUT: FADH2
What is step 6 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Fumarate (4C) to Malate(4C)
Enzyme: Fumarate Hydratase
IN: H20
OUT: Nothing
What is step 7 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Malate(4C) to Oxaloacetate (4C)
Enzyme: Malate dehydrogenase
IN: NAD
OUT: NADH + H+
What is step 8 of Kreb’s cycle, the enzyme, and what goes in and out?
Process: Oxaloacetate (4C) to Citrate (6C)
Enzyme: Citrate synthase
IN: acetyl coA + CO2 +H20
OUT: Coenzyme A
How much ATP is generated by respiration?
There is debate as to how much ATP is produced from glycolysis, Kreb’s cycle and Oxidative phosphorylation but its roughly between 34-38 ATP molecules (the
number 38 is theoretical and assumes all of the NADH produced in glycolysis & the Kreb’s cycle enter into oxidative phosphorylation AND all the free hydrogen ions are used in the chemiosmosis for ATP)
What is embedded in the inner mitochondrial membrane surface?
Cytochromes (contain iron and copper co-factors, structure resembles the red iron-
congaing haemoglobin) and associated proteins embedded in the inner mitochondrial
membrane surface form the components of the electron transport chain
How does oxidative phosphorylation regenerate coenzymes for Kreb’s and Glycolysis?
Two electrons from hydrogen atoms are initially transferred either from NADH + H+ or
FADH2 to one of the protein in the electron transport chain.
These electrons are then successively transferred to other compounds in the chain redox reactions, until the electrons are finally transferred to molecular oxygen, which then combines with hydrogen ions (protons) to form water.
in addition to transferring the coenzyme hydrogens to water, this
process also regenerates the hydrogen-free forms of the coenzymes (NAD+ &
FAD), which can then become available to accept two more hydrogens from
intermediates in the Kreb’s cycle, glycolysis or beta-oxidation.
What enzyme is embedded in the inner mitochondrial membrane and what is its role?
Embedded in the inner mitochondrial membrane are enzymes called ATP synthase.
This enzyme forms a channel in the membrane, allowing hydrogen ion to flow back
into the matrix via chemiosmosis - moving from an area of high concentration of
hydrogen ions to an area of low concentration. During this process, the energy of the
concentration gradient is converted into chemical bond energy by ATP synthase,
which then catalyses the formation of ATP from ADP and Pi
How many molecules of ATP are produced per round of oxidative phosphorylation?
The transfer of electrons to oxygen produces on average around 2.5 and 1.5
molecules of ATP for each molecule of NADH + H+ & FADH2 respectively
Quick summary of respiratory acidosis?
Slow down, retain CO2
Quick summary of respiratory alkalosis?
hyperventilate and blow off CO2
Quick summary of metabolic acidosis?
retain H+, excrete HCO3-
Quick summary of metabolic alkalosis?
Excrete H+, retain HCO3-
What is the anion gap?
the difference in serum concentration of cations (positive) and anions
(negative) e.g. Cl-, HCO3 -, Na+, K+ - Equation: (Na+ + K+) - (HCO3- + Cl-)
- Not all ions are included e.g. K+, PO4 -, SO4 -
- Normal value is between 3-11mEq/mol
- Can be used to help diagnose cause of metabolic acidosis - if there is a high
anion gap or normal anion gap - can be used to see if cause is excessive loss of
bicarbonate or excess H+ production etc.
What are the four reactions of the Haber-Weiss Cycle?
- Fe2+ + H2O2 > Fe3+ + OH- + OH• [Fenton reaction]
- OH• + H2O2 > H2O + O2•– + H+
- O2•– + H+ + H2O2 > O2 + OH• + H2O [Haber-weiss reaction]
- Fe2+ + OH• + H+ > Fe3+ + H2O
Which ROS is the most potent?
Hydroxyl Radical
What can be damaged by free radicals?
Free radicals damage; proteins, lipids, carbohydrates & nucleic acids
- They damage membranes of; cells, nucleus, mitochondria & endoplasmic reticulum.
This cell membrane damage results in the increased permeability of the membrane
resulting in an influx of calcium, water & sodium
- DNA can also be damaged by the hydroxyl radical - this results in strand breaks &
base alterations - MUTATIONS
What diseases are associated with free radical damage?
Emphysema, Parkinson’s, Acute renal
failure & Diabetes
What is the respiratory burst?
- Immune system defence against bacteria
- Sudden release of ROS by immune cells (neutrophils, macrophages & monocytes)
during phagocytosis. - Immune cells utilise NADPH oxidase to reduce oxygen to superoxide
- Superoxide is released (which is then reduced to hydrogen peroxide, which in turn can be reduced to hydroxyl radical etc.), which then generates other reactive oxygen species
- Neutrophils & monocytes use myeloperoxidase to
further combine H2O2 with Cl- to produce hypochlorite
(ClO-) [H2O2 + Cl- > H2O + Cl-] which plays a role in
destroying bacteria by damaging bacterial cell
What are the characteristics of the superoxide radical?
Produced by electron transport chain
Generates other radicals locally
What are the characteristics of hydrogen peroxide?
H2O2 Generates radicals with transition metals
Lipid soluble
What is the consequence of an impairment to NADPH oxidase?
prevents the formation of ROS
and causes chronic granulomatous disease (X-linked) (build up of pathogens in
phagocytes since they can engulf but NOT kill them - leads to severe skin
infections with bacteria or fungi)
What protections are available against ROS?
- Antioxidant enzymes:
• Superoxide dismutase - converts superoxide to hydrogen peroxide (non toxic unless
converted to another ROS) & oxygen
• Catalase - catalyses conversion of hydrogen peroxide to water & oxygen and protects
white blood cells against own respiratory burst
• Glutathione Peroxidase - catalyses the reduction of hydrogen peroxide to water
and a disulphide (GSSG) - Antioxidant vitamins: Vitamin E - found in liver, free radical scavenger, protects
against lipid peroxidation and terminates free radical propagation in
membranes, Vitamin C - e.g ascorbic acid, reacts with superoxide & hydroxyl
radical and regenerates reduced vitamin E - Cellular compartmentalisation - respiratory burst taking place in phagosomes so
harmful chemicals don’t get out and damage healthy tissue
What is the rate limiting step in Kreb’s Cycle?
Therate-limiting stepof thecitric acid cycleis catalyzed by theenzyme, isocitrate dehydrogenase
