Cell Functions - AP Biology

ATP synthase, the enzyme responsible for ATP production on the inner mitochondrial membrane, depends on the proton gradient produced by the electron transport chain (ETC). If the proton gradient is disrupted, not as many ATP can be produced.

NADH and FADH2 are essential to the function of the electron transport chain as electron donors, and are produced during glycolysis and the Krebs cycle to facilitate this process. Electron donation from these compounds is what fuels the formation of the proton gradient, while decreases in these compounds can cause uncoupling.

Remember that NADH and FADH2 are electron carriers and do not directly create any energy. The movement of the electrons through the electron transport chain also does not create energy directly, but does create a proton gradient that is later used to create energy. The movement of protons down its proton gradient through ATP synthase does, however, generate energy. It actually generates around 30 ATP molecules per one glucose.

In both cellular respiration and photosynthesis, chemiosmosis occurs. Chemiosmosis is the process in which the creation of a proton gradient leads to the transport of proton down its concentration gradient to produce ATP. This occurs in the electron transport chain in both mitochondrias and chloroplast. In the photosynthesis it occurs when the electron is transported from photosystem II to photosystem I.

The laws of inheritance include the laws of segregation (each gamete receives only one copy of each gene from its parent), dominance (in a heterozygote individual, only the dominant allele will influence the phenotype), and independent assortment (inheritance of one gene does not influence inheritance of another gene)

The law of independent assortment states that inheritance of one gene does not influence inheritance of another gene. Thus, inheritance of seed color does not affect the inheritance of seed shape.

According to the Law of Segregation, each gamete receives one allele for each gene from each parent. During Meiosis, each parent’s two copies of each allele are separated from each other, then the gamete receives one copy of each allele from each parent (for a total of two alleles).

This is the definition of the law of independent assortment; during meiosis, the inheritance of one gene does not influence whether another, separate gene will also be inherited by that gamete.

According to the Law of Dominance, each individual has two alleles for each trait and only the dominant allele contributes to the phenotype.

According to the Law of Segregation, during Meiosis, homologous chromosomes segregate into different gametes.

Recombination or crossing over happens primarily in Prophase I. In anaphase and telophase, the DNA strands are separated and cannot recombine. In metaphase, homologous chromosomes line up with each other, but do not recombine.

Mitosis and meiosis share many procedural similarities, however, it is important to remember that mitosis makes identical cells while meiosis allows genetic variability between cells.

Meiosis takes place in sex cells, which are capable of creating millions of different variations of offspring. Mitosis takes place in normal cells involved in growth and regeneration within a single, uniform organism.

Meiosis includes two divisions, resulting in two pairs of haploid cells, while mitosis only involves a single division.

Both meiotic and mitotic divisions share the same phases, though there are some differences in the activity of these phases. Mutation can, and does, occur in both mitosis and meiosis. Crossing over, however, is unique to meiosis.

Crossing over ensures genetic variability as it results in daughter cells with different genetic material than their parent cells. This occurs during meiosis I, but is not seen in mitosis or meiosis II.

Both mitosis and meiosis occur in humans. Somatic cells (body cells) divide via mitosis, while gametes (sex cells) divide via meiosis. Because of actions such as crossing over, meiosis results in a higher genetic variability than mitosis.

Prokaryotes, such as bacteria, reproduce asexually, and are incapable of meiosis.

Turner syndrome occurs when a person is missing one sex chromosome, and only has one X-chromosome. As a result, they will be female, and may suffer a variety of symptoms. This is an example of monosomy, in which a person only has one chromosome, when they should have two.

The other three choices are examples of trisomy. Klinefelter is an instance of sex-linked trisomy, with a karyotype of XXY. Down syndrome is cause by trisomy 21, and Edwards syndrome is caused by trisomy 18.

Non-disjunction occurs when sister chromatids fail to separate during meiosis, leading subsequent daughter cells to have an unequal number of chromosomes. This can result in a cell having one extra chromosome (trisomy), or missing one chromosome (monosomy).

The following shows non-disjuction occuring in metaphase II of meiosis. "X" represents a chromosome, "|" represents a cell membrane, and "\" and "/" represent chromatids. When a sperm cell fuses with the egg formed to the left of the membrane (|), it will result in trisomy. When a sperm fuses with the egg to the right of the membrane (|), it will result in monosomy.

Metaphase I: X X

Telophase I: X | X

Metaphase II: / \

Telophase II: / \ |

The most acidic environment, or the lowest pH, would be found in the intermembrane space. This is because as and pass their electrons to the enzymes in the electron transport chain, protons are pumped into the intermembrane space. This is where a high concentration protons is generated, which is considered acidic. The low concentration of protons is generated in the mitochondrial matrix rendering it basic.

The final electron acceptor in the electron transport chain is oxygen. It gets reduced by accepting two electrons and two protons from the ATP synthase to form water via the following equation:

Each produces 3 molecules in the electron transport chain while each produces 2 molecules. Each glucose molecule results in the formation of 10 molecules, which go on to produce 30 . Each glucose molecule results in the formation of 2 molecules, which go on to produce 4 . Note that some references may indicate that each produces 2.5 , while each produces 1.5 . These are theoretical maximums and depend on the organism, cell type, and cellular environment.