Writing in Biology

Lucy's skeleton was found by Donald Johanson and Tom Gray in 1974 in Ethiopia. An ulna was spotted that was identifued as a hominid, a long period of excavation began which presented them with forty percent of a single hominid skeleton. This skeleton is a member of the family Hominidae which encompasses all species originating after humans and ape's split. A defining characteristic of all hominids is that they are able to walk upright and have bipedal locomotion. There legs lie directly underneath their pelvis. Lucy showed key characteristics that pointing to bipedality. Her skeleton is approximately 3.2 million years old.

Gene therapy is known as the ability for gene improvement by altering genes usually for the purpose of treating a disease. A normal gene is inserted into a genome which then replaces an abnormal gene. There are multiple gene therapy protocols that have been approved for clinical use although some have been successful there is still a lot left to understand. Two specific types of gene therapy are germline gene therapy and gene therapy of somatic cells, the key difference being that using somatic cells so future generations can’t inherit it, which is not the case for germline gene therapy. Some difficulties that arise with gene therapy is that a vector is needed in order to release the gene into the stem cell. This vector is a very specific one which cannot elicit a response from the immune system and has to be able to be produced in a large scale. The vector has to express the gene for the patient’s entire life.

Phloem is like plant’s version of blood-it transports nutrients up and down the plant. Extra phloem is sent to the roots for storage. Force is generated at the source-where the nutrients are going (also by where they are coming from). Phloem forces are positive pressure. The destination generates pressure lower than source-all positive pressures, no tension. Phloem cells are much smaller and have thinner cell walls than xylem. The outer part of phloem gives structure-bundle sheath. The primary phloem is the first phloem-first formed.  The secondary phloem is made after primary a d comes after vascular cambium. In between shoot meristem and root meristems are primary tissues, xylem and phloem differentiate after these points. In a tree, a new meristem differentiates in the trunk-this is the cambium which makes new cells (trees).

Sieve cells are called this because the tubes act as one continuous cell and are a collection of sieve tube elements. They tend to look empty, have very prominent joints, are very long and don’t have a nucleus (like xylem, but are living cells). They don’t have a cytoskeleton, have very few organelles (probably no Golgi, plastids or lignin; some ER, few mitochondria, have plasma membrane). Companion cells, ordinary cells that feed sieve cells and keep them alive, are next to sieve cells. A ‘sieve plate’ is the wall in between each sieve cell. Sieve plates contain special clotting proteins and polysaccharides which should only be released when the phloem is damaged. They are like slime and are very prominent; these are phloem clots that stop the flow of nutrients if the phloem is damaged. 

Gymnosperm phloem does not have sieve tubes, only single cells. Sieve plates are on the side of the cell-works like a network rather than a pipe. These are called sieve areas. It is not understood how this works because sieve areas are filled with endoplasmic reticulum which blocks flow. The presence of membranes would mean that there can’t be a bulk flow, but it doesn’t seem to be possible in gymnosperms.

The conclusion of the study was that soil temperatures at or above 23 degrees C inhibit root growth and respiration both long and short term in A. stolonifera,and the specific maintenance respiration rates of A. stoloniferawere significantly higher than A. scabraat higher temperatures. Increased soil temperatures actually caused A. scabrato thrive and it can survive higher temperatures. The original hypothesis was supported.

The purpose of this study was to determine how rising temperatures (due to climate change) are affecting root growth, plant survival, carbohydrate metabolism, and root respiration rate in environments where plants are very temperature sensitive, and to better understand how roots maintain growth and function under high soil temperature conditions. The hypothesis was that A. stoloniferawould have lower root respiration responses than A. scabraat higher temperatures.

It is important to understand how roots respond to temperature because it can affect root and relative growth rate, and in species with roots sensitive to temperature change, growth can be affected negatively. In this study, two species of grass were tested, one whose roots were more heat-sensitive and one whose roots were not. This was to see if species with heat sensitive roots would be affected greater than species whose roots are not heat sensitive. A. scabrais a known grass that thrives at very high soil temperatures, while A. stoloniferais a high-temperature sensitive grass grown in cool climates.

In class, we learned about different types of cytoskeletal filaments. We covered intermediate, actin, and microtubules. Intermediate filaments are only found in some animals, have a high tension capacity, and are made up of 8 tetramers stacked on top of each other. They have no directional polarity. Since they do not have polarity, they do not have any motor proteins. They also have no DNA triphosphate on them, so they are not dynamic filaments.

Actin filaments are highly dynamic and easily reorganized. They are 9 nanometers in diameter. Their subunits are called G actin and when in a polymer it is called F actin. A free actin subunit is bound to ATP while in the polymer it is bound to ADP instead. It also goes under a conformational change when incorporated into a filament. Actin has directional polarity where new subunits can be added or taken from each side. The plus end grows and shrinks faster than the minus end in that respect. 

Microtubules themselves have a negative charge and are 25-30 nanometers in diameter, forming hollow tubes, The subunit is a heterodimer of alpha tubulin and beta tubulin. It has directional polarity where the beta tubulin faces the plus end and alpha tubulin faces the minus end. Microtubules are dynamic and rearrange into mitotic spindle during mitosis or can form cilia for cell movement. With its polarity, it also has motor proteins going along it. Dyenin is a minus end motor protein and kinesis is a plus end motor protein. 

For proteins to get into the nucleus, it requires a Nuclear Localization Sequence (NLS). This NLS has a chain of positive amino acids in the sequence that the nuclear pore complex can recognize and let the protein through to the inside of the nucleus. To let it in, the protein with the NLS, importin Alpha and Beta bind to it. Once in the nucleus, RAN GTP binds to importin and importin Beta leaves the protein with the NLS. Some proteins that are less than 50kDa to pass through the nuclear membrane through diffusion. Also, in the nuclear import, the signal sequence is not removed and the protein does not need to be unfolded. 

For the transport into the ER, a long sequence of hydrophobic amino acids are required. When the protein travels to the ER for import, the signal sequence is cleaved off and the protein unfolds. Once in the ER lumen, it refolds but the protein is shorter since the signal was clipped off.