This is how proteins are manufactured and secreted in cells.
Amino acids pass through the plasma membrane by diffusion down a concentration gradient or by active transport. They then combine with their specific tRNA. They are then transported to ribosomes attached to the rough endoplasmic reticulum, where they are incorporated into a polypeptide via protein synthesis. The protein molecule is then packaged into a transport vesicle, which pinches off from the rough endoplasmic reticulum. The vesicle transports the protein molecule to the Golgi apparatus where it fuses wiht the cis face of the Golgi apparatus. Protein is chemically modified as it moves through the Golgi apparatus, undergoing post-translational modification. Trans face gives rise to vesicles containing the inactive form of the protein. The secretory vesicle eventually buds off from the secreting face of the Golgi apparatus. When vesicles reach the cell surface, it fuses with the plasma membrane, and releases the inactive protein by exocytosis, using ATP in the process.
Tuesday, November 4, 2008
Respiration
Respiration is the breakdown of large glucose molecules into simple molecules such as carbon dioxide and water with the simultaneous release of energy inside living cells. It is an enzyme mediated process.
Main processes:
Glycolysis (glucose to pyruvate, occurs in cytosol)
Link Reactions (pyruvate to acetyl CoA, occurs in intermembranal space)
Krebs cycle (acetyl CoA to carbon dioxide, occurs in the matrix)
Oxidative phosphorylation (occurs in the inner membrane)
Main processes:
Glycolysis (glucose to pyruvate, occurs in cytosol)
Link Reactions (pyruvate to acetyl CoA, occurs in intermembranal space)
Krebs cycle (acetyl CoA to carbon dioxide, occurs in the matrix)
Oxidative phosphorylation (occurs in the inner membrane)
Calvin Cycle
The Calvin cycle is also known as the light independent reactions, as they can occur in the dark. It occurs inside the stroma of the chloroplasts. There are three stages: carbon dioxide fixation, reduction of carbon dioxide, and regeneration of ribulose biphosphate.
Carbon dioxide is initially accepted by ribulose biphosphate to become a 6 carbon unstable intermediate, which breaks down to form two molecules of 3 phosphoglycerate. This reaction is catalysed by RuBP carboxylase, or Rubisco. 3-phosphoglycerate is later phosphorylated by a molecule of ATP to form 1,3-biphosphoglycerate and ADP. 1,3-biphosphoglycerate is later reduced by NADPH to form phosphoglyceraldehyde (GALP) and NADP. 1/6 of all GALP formed is channelled to form sugars and other useful substances for the plant. The remaining 5/6 of GALP undergoes a series of chemical reactions and is phosphorylated by ATP again to regenerate RuBP.
Carbon dioxide is initially accepted by ribulose biphosphate to become a 6 carbon unstable intermediate, which breaks down to form two molecules of 3 phosphoglycerate. This reaction is catalysed by RuBP carboxylase, or Rubisco. 3-phosphoglycerate is later phosphorylated by a molecule of ATP to form 1,3-biphosphoglycerate and ADP. 1,3-biphosphoglycerate is later reduced by NADPH to form phosphoglyceraldehyde (GALP) and NADP. 1/6 of all GALP formed is channelled to form sugars and other useful substances for the plant. The remaining 5/6 of GALP undergoes a series of chemical reactions and is phosphorylated by ATP again to regenerate RuBP.
Q: Describe semi-conservative replication
A segment of DNA is unwound by helicase. H-bonds between both strands are broken. Primers are laid down by primase in the 5' to 3' direction. DNA polymerase III adds complementary free nucleotides to 3' growing end.
Link Reactions
The Link Reaction is a process of respiration and occurs in the intermembranal space of mitochondria. It involves the oxidative decarboxylation of pyruvate to form acetyl CoA. NAD is reduced to form NADH and a proton.
Genetic terms
Genotype is the genetic composition of an organism.
Phenotype is the set of characteristic manifested by an organism.
An individual has a heterozygous condition if he has 2 different alleles of the same gene
An individual has a homozygous condition if he has 2 identical alleles of the same gene.
Codominance is a genetic interaction where the codominant alleles of a gene express themselves equally in the phenotype
Dominance is a genetic interaction where 1 allele of a gene masks the expression of another allele in the heterozygote.
Locus is the position of a gene in a DNA molecule of a chromosome
A gene is the functional unit of inheritance
An allele is an alternative form of a gene.
Phenotype is the set of characteristic manifested by an organism.
An individual has a heterozygous condition if he has 2 different alleles of the same gene
An individual has a homozygous condition if he has 2 identical alleles of the same gene.
Codominance is a genetic interaction where the codominant alleles of a gene express themselves equally in the phenotype
Dominance is a genetic interaction where 1 allele of a gene masks the expression of another allele in the heterozygote.
Locus is the position of a gene in a DNA molecule of a chromosome
A gene is the functional unit of inheritance
An allele is an alternative form of a gene.
Stem cells
Stems cells are unspecialized cells that are capable of continually renewing and dividing through cell division for long periods. They are also capable of differentiating into specialized cell types under appropriate conditions. Therefore the two normal functions are to reproduce and give rise to more cells indefinitely (in the case of 3 to 5 day old blastocyst), and to regenerate multiple types of cells to replace those that have died or were damaged (where there is a local infection/injury).
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