Cell Organelle Structures and Functions

Task 1:

Question 1:

Question 2:

The following phases mentioned are parts of interphase during which the cell prepares to divide.

G0 phase: The G0 phase is called the resting phase of the cell in which the cell remains in a quiescent state and it is regarded as the extension of the G1 phase. The cells remain in this phase until a signal is received by them for involving in cell division (Kashyap et al. 2016).

G1 phase: The G1 phase is regarded as the growth phase in which the synthesis of different enzymes and nutrients occurs after the cell receives signal to divide (Liu et al. 2016).

S phase: The S (synthesis) phase is referred to the step in the cell cycle in which replication of the DNA starts in the cell occurs so that the genetic material in the cell can be doubled to form two sister chromatids (Kim et al. 2015).

G2 phase: The cell at the end of S phase enters the G2 (gap2) phase in which the cell continues its production of protein and replication (Jones et al. 2018).

M phase: The cell on entering the M phase divides into two cells where each cell receives copied DNA and the cytoplasm (Jones et al. 2018). In case the cells are found to be damaged at this stage, they are sent back to the G0 phase.

Question 3:

The role of the checkpoint before the G1/S phase is to check the proper DNA formation of the cells so that it produces healthy daughter cells and undamaged DNA to maintain cell integrity (Liu et al. 2016). Thus, at this point it is decided whether or not the cell is to enter division. In case the start checkpoint of the cell is kept in ON position on permanent basis, then it would lead damaged cell to enter the multiplication phase leading to the formation of damaged organisms (Liu et al. 2016).

Question 4:

The mitosis is referred to the cellular process which occurs to develop two daughter cells from a single cell. The following phases of mitosis:

Question 5:

The three general properties of stem cells are that they are able to divide and renew them for longer time (self-renewal), unspecialised in nature and is able to give rise to any nature of specialised cell in the body (potency) (Conde et al. 2016). The four key types of stem cells are embryonic stem cell, mesenchymal stem cell, tissue-specific stem cell and induced pluripotent stem cell. The role of embryonic stem cells on proper signalling is to mature into any specialised cells to function as muscles, blood, bone, neurons and other types of cells. They are regarded as pluripotent (Ouyang et al. 2016). The role of tissue-specific stem cells is to replace damaged cells from tissues (skin, the inner lining of gut and blood) that are lost due to normal process or day to injury (Visvader and Clevers, 2016). The induced pluripotent stem cells which are developed from the blood or skin cells have the role to develop unlimited source of any nature of human cell required for the therapeutic process (Hockemeyer and Jaenisch, 2016). The role of mesenchymal stem cell is to repair and make skeletal tissues such as bone, cartilage and fat in the bone marrow as well as acts in immune-modulation function (Spees et al. 2016). In the current era, the stem cells are used as transplants to replace damaged cells of the body in chemotherapy that is provided to cancer patients. They are also used for fighting some of the diseases such as lymphoma, multiple myeloma, neuroblastoma and leukaemia of the donor. In future, the stem cells are planned to be used cloning and formation of functional organs to replace them with the damaged organ in the body of humans. However, the process is regarded to be complicated in nature and will need international and interdisciplinary collaboration. The impact of stem cell in future would be that people can be able to experience less harm from Parkinson, Alzheimer, heart disease, diabetes and others as the stem cells are to be used for repairing neurons and brain cells to ensure healthy living of the individuals (Dragu et al. 2015).

Question 6:

The stem cell decision to form any type of cell that is the fate of the cell is signalled through chemicals, hormones, an extracellular protein, the physical environment and others. The embryonic stem cells become specialised through proper gene expression. The gene expression is regarded as the process in which protein through the cellular process is created that is directed by the DNA sequence in the gene. In embryonic cells, there are different DNA sequences and they are found to have the ability to give rise to different set of proteins based on the nature of cellular signal and environment provided to them. The gene through transcription initially produces an mRNA and it travels to the nucleus of the cell in dictating the specific proteins to be developed in making the specialised cell (von Erlach et al. 2018). For example, stem cells which are present in the bone marrow are called hamocytoblasts which through genetic expression and cell signalling decides to either develop into a myeloid stem cell or lymphoid stem cell. The myeloid stem cell gives rise to myeloblast and red blood cells along with blood platelets (Giani et al. 2016).

Question 7:

In cell biology, the active transport is the process in which molecules passes through the cell membrane from lower concentration to higher concentration that is against the concentration gradient and this process needs energy in the ATP (Shih et al. 2019). One of the examples of active transport is the transportation of glucose in the small intestine. In this process, the microvilli present in the inner lumen of the small intestine which is made up of epithelial cells absorb glucose through the sodium-potassium pump by using ATP (Adenosine Tri-phosphate) as an energy source. The sodium-potassium pump leads the intestinal cells to lose three Na+ ions for two K+ ions creating a loss of positive charge within the cell. This leads the cell to receive glucose and 2 positive Na ions to manage the inner electric charge of the lumen (Kiela and Ghishan, 2016). The passive transport is referred to the process in which ions, as well as other atomic substances and molecules, moves from an area of high concentration to an area with low concentration which means acting with the gradient (Vermaas et al. 2019). One of the examples of passive diffusion is when alcohol enters the body it immediately hits the bloodstream making the person feels drunk. This is because the molecules in the alcohol are more concentrated than the molecules in the blood which leads them immediately enter the bloodstream to maintain a stable environment (Paton and McCune, 2015).

Task 2:

Question 1:

The semi-conservative DNA replication is referred to as the mechanism through which replication of DNA occurs in all individuals. The first step of this replication includes replicated fork formation which means that the double-stranded DNA is unzipped into single strands of two indicating each strand has four bases which as adenine (A), thymine(T), guanine (G) and cytosine (C). It is to be considered that A only forms pairs with T by using two hydrogen bonds and C only bind with T by using three hydrogen bonds. The unwinding of the DNA is done through DNA helicase which acts to break the hydrogen bond present between the mentioned base pairs. One of the unwinded strands of DNA contains a 5' to 3' direction and another contains 3' to 5' direction (3' has hydroxyl group and 5' has phosphate group) (Takikawa et al. 2016). In the second stage, a short RNA known as primer binds at the 3' end of each of the two strands of DNA and the generation of primer occurs through the help of DNA primase. The third step includes elongation in which with the help of DNA polymerase the new strand is formed on each unwinded strand of original DNA. The DNA polymerase III has the key function to replicate whereas DNA polymerase I, II, IV and V have the function to check error in replication and repair (Lai and Pugh, 2017). The lagging strand initiates to replicate by binding many primers and DNA polymerase adds pieces of DNA known as Okazaki fragments in between the strand and the polymer. The newly formed strand is not continuous and is fragmented. The fourth step includes termination in which the enzyme known as exonuclease acts to remove primer of RNA from the original DNA strands so that they can be replaced with proper bases. The DNA ligase acts to link the Okazaki fragments to form a continuous DNA strand. Thus, it leads the formation of two copies of DNA in which one strand is original and another is newly formed strand (Kaempfer, 2017).

Question 2:

The central dogma of molecular biology is referred to as the flow of sequential genetic information in a biological system between information carrying biopolymer that is DNA makes RNA and protein are made from RNA. The information can be transported back from the protein or to the nucleic acid (Duncan et al. 2016). Thus, it informs that three major classes of biopolymer are protein, RNA (Ribonucleic Acid) and DNA (Deoxy- Ribonucleic Acid). The central dogma classes these biopolymers into three groups that are three special transfers, three general transfers and three unknown transfers. The special transfers include DNA synthesis occurs through the use of RNA template, RNA is able to be replicated from RNA and protein synthesis occurs by using information in the DNA and not requiring the use of mRNA. The general transfers are referred as the process in which normal flow of biological information occurs that is DNA is able to be copied into another DNA through replication, protein is able to be produced by using information stored in the mRNA and mRNA is able to copy the information present in DNA. The unknown transfers include synthesis of DNA and RNA by use of primary protein structure as well a protein is able to be copied from another protein (Koonin, 2015; Marshall, 2017).

Question 3:

The DNA (Deoxy-Ribonucleic Acid) which is the universal genetic code is present in all organisms that are living. The DNA is mainly made up of 4 nucleotides which are Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). Among the organisms who are living on the earth, it is seen that they have the same sequence of genetic code present be it animal or human. This indicates that the codons which are mentioning the amino acids present in the cell are the same in humans as well as the bacteria which is living in the hydrothermal vents. In few organisms, a small difference is the code is seen such as change in the amino acid that is encoded by a certain codon (Koonin and Novozhilov, 2017). Thus, the code is present in the same manner among all individual on earth so it is regarded as the universal code. The code is important to gather evidence and proof of common origin of any life on earth as the code is significant to cell functioning and change in the code would result in key alterations within organisms making them unsuitable to live on earth. Moreover, the universal code can be able to explain the key similarity of the genetic codes present across organisms in the current era (Keeling, 2016).

Question 4:

The first step of genetic expression is transcription and it occurs within the nucleus of the cell. The first stage of transcription is known as the pre-initiation stage in which a bubble is formed by unwinding the DNA strands with the help of RNA polymerase enzyme and its co-factors. In approx, 14 bases are usually exposed each time. In the initiation stage, the RNA polymerase enzyme is seen to binds with the promoter region of DNA. The binding signals unwinding of the DNA strands to make complementary strands of mRNA. In the promoter clearance stage, the promoter on the DNA strand is cleared by the RNA polymerase after the first bond is established. In the elongation stage, the nucleotides are added to the mRNA (messenger RNA) strand with the RNA polymerase reading the DNA strands. In this stage, there is time when Adenine of DNA strands binds with Uracil of RNA strand. The third stage includes termination in which the RNA polymerase stops formation of sequence and the mRNA formed is detached from DNA (Nogales et al. 2016; Venkatesh and Workman, 2015). Thus, it is the process in which information from the DNA strand is copied to new molecule of messenger RNA (mRNA).

Question 5:

In cell biology, translation is referred to the process that leads the ribosome present in the endoplasmic reticulum or cytoplasm to synthesise protein after DNA or RNA transcription within the nucleus of the cell (Ingolia, 2016). The first step of translation is initiation in which the ribosomes are seen to bind with the mRNA at the initial codon that is AUG which is recognised as the only initiator tRNA. The next step is elongation and in this phases, the ribosomes proceed to execute protein synthesis. This is done by forming complexes made up of amino acid that is linked with the tRNA (Zarai et al. 2016; Ingolia, 2016) which are then sequentially bound to the proper codon in the mRNA through the formation of complementary base pairs with the anticodon of tRNA. The process progress with ribosome moving from one codon to another with mRNA and the addition of amino acid occurs that are translated into polypeptide sequence directed by DNA and represented by the mRNA. The termination stage is the last stage in which a release factor attaches with the stop codon resulting to terminate translation and releasing completely formed polypeptide from the ribosome (Brar and Weissman, 2015).

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