Cell Biology Essay by Meera Patel PDF

Preview

Summary

Download Cell Biology Essay by Meera Patel PDF

Description

Cell Biology Essay by Meera Patel Cell structure Cells are known as the basic unit of life for all living organism, from the simplest microorganism to complex plants and animals are all made of cells. The cells in these organisms have similar characteristics that are needed for function and survival. The main characteristics include:  Movement- so that they can move and change position.  Reproduction to produce the same organisms.  Sensitivity to detect and sense stimuli and to respond to them.  Respiration to produce chemical reactions which break down molecules in the cells and release energy.  Nutrition to take in and absorb nutrients for example ions that contain raw materials needed for growth and repair.  Excretion to remove toxic materials and waste products (Characteristics of living organisms - Variety of living organisms - GCSE Biology (Single Science) Revision BBC Bitesize, 2020)

Image 1: Animal cell structure.

Image 2: Plant cell structure    Prokaryotic and Eukaryotic cells Single cell structures are known as Eukaryotic or Prokaryotic cells. The difference between the two is that Eukaryotic cells have a nucleus and are multicellular organisms such as plants, animals and fungi. Prokaryotic cells are organisms such as bacteria are unicellular. The structure of prokaryotic cells are surrounded by a plasma membrane and do not have internal membrane bound organelles in the cytoplasm. The DNA in prokaryotic cells includes no histones or chromosomes and are contained within a nucleotide. Prokaryotes includes smaller DNA molecules called plasmids. Eukaryotic cells are complex structures of plants, animals and fungi. Eukaryotic cells have a nucleus and is where DNA is contained. The DNA in eukaryotic cells include proteins called histones which are sorted into chromosomes.

   Image 3: Shown in the diagram is the difference between Prokaryotic and Eukaryotic cells. Viruses are defined as microorganisms that infect living organisms. Viruses lack the characteristics present in eukaryotic and prokaryotic cells such as they have no cells, are unable to reproduce and have no metabolism or stimulus response. Two ways that Viruses reproduce by either lytic and lysogenic cycle. In lytic cycle the virus binds to the surface of the host cell and inserts its genetic material into the cell. The Lytic cycle takes place when the host cell bursts and they then infect other cells. In lysogenic cycle the viral binds to the surface of the cell and inserts its DNA into the host cell, the virus DNA replicates every time the cell replicates.

Image 4: Virus structure

In conclusion eukaryotic and prokaryotic cells are similar as both contain a plasma membrane which contain cytoplasm and ribosomes. Both contain DNA which have the same genetic code, however some materials that are present in eukaryotic cells are not present in prokaryotic cells for example mitochondria, lysosomes and nucleus this is because eukaryotic cells are complex.

Eukaryotic sub-cellular structure and organelles Eukaryotic cells contain membrane bound organelles; these organelles have different roles within the cell. Eu k a r y ot i cc e l l si n c l u demi t o c h o nd r i aa n dt h en umb e rv a r i e sa c c o r d i n gt ot h e s i z ea n dt y p eo ft h ec e l l .Mi t o c h o n d r i af u n c t i o ni st os u p p o r tt h epr o t e i nsi nt h ee l e c t r o t r a n s p o r tc h a i no ft h ea e r o b i cr e s p i r a t i o nb ys u pp l yi n gt hec e l lwi t hATP .Th ee nd o p l a s mi c r e t i c u l um i n c l u d es mo ot ha n dr o u g h . Rou g h En d o p l a s mi cr e t i c ul um i n c l u de a t t a c h e d r i b o s o me sa n dt h er o l ei st oc o mp a r t me n t a l i s et h ec e l la ndt r a n s p o r tp r o t e i n sa n dl i p i d s . Smo o t he n d o p l a s mi nr e t i c u l u mr o l ei st op r o du c en e wl a y e r sofg o l g ib o d i e st h e i rr o l ei s p r oc e s s ma t e r i a l s wh i c ha r ep r o du c e db yt h ec e l la nd t h e s eg ol gib o di e sa r es t a c k s o fs c a c skn o wna sCi s t e r n a e . Pr o k a r y o t i ca n de u ka r y o t i cc e l l sh a v ema n y r i b o s o me s ,  b u tt h er i b o s o me so ft h ee uk a r y o t i c c e l l sa r el a r g e ra n dmor ec omp l e xt ha nt h o s eo ft hep r o ka r y o t i cc e l l .Ri b o s o me sa r ema d eup o fs p e c i a l i s e dRNA mol e c ul e sa n das p e c i ficc o l l e c t i o no fd i ffe r e n tp r o t e i n s .Eu k a r y o t i c r i b o s o mei sma d eupo ffiv et y p e so fr RNAa nda p p r o xi ma t e l ye i g h t yt y p e so fp r o t e i n s .   Th ec y t o p l a s mo fe u k a r y o t i cc e l l sc o n t a i nsac o mp l e xc o l l e c t i o no fo r g a n e l l e sa n dma n yo f t h eo r g a ne l l e sa r ee n c l o s e di nt he i ro wn me mb r a n e s .  Th ep r o ka r y o t i cc e l lc on t a i n sn o me mb r a ne b o un do r g a n e l l e st h a ta r ei n d e p e n d e n to ft h ep l a s mame mb r a n e .   A p r o k a r y o t i c c e l lc o n t a i n s  s p e c i a l i s e d c o mp o un d s i n t h e f o r m o fg r a n u l e s o r d r op l e t s .  Al t h o u g h e u k a r y o t i c c e l l s t or e s g l y c o g e n , s t a r c h , l i p i d a nd i n s o me c a s e s  s p e c i a l i s e d ma t e r i a l so fo r g a n i s ms .  Pr o k a r y ot i cc e l l sa r ef o u n di nba c t e r i aa n db l u egr e e n a l g a e , e u k a r y o t i cc e l l sa r ef o un di nf u n g ip l a n t sa n da n i ma l s . To s u mma r i s e ,p r o ka r y o t i ca n de uk a r y o t i cc e l l sa r es i mi l a ri nt h ef a c tt h a tt he yb o t ha r e c o n t a i n e db yp l a s mame mbr a n e s ,fil l e dwi t hc y t o p l a s ma n dc o n t a i nr i b os o me s .Ho we v e r ,  t h e y h a v ema n yma t e r i a l sp r e s e n ti nae u ka r y o t i cc e l lwhi c ha r en o tp r e s e n ti nap r o k a r y o t i cc e l l . Th i si sb e c a u s eae u k a r y o t i cc e l li smuc hmor ec ompl e xa n dh a v ema n ymo r ef u n c t i o n st o c o mp l e t e .     

The role of the cell membrane in regulating how nutrients are gained and waste products lost. The cell membrane is defined as a biological membrane that separates the interior of the cell for example the cytoplasm from the exterior environment and protects the cell from the environment. It is known to be selectively permeable and is made up of phospholipid bilayers a double layered membrane by placing fatty hydrophobic tails in the inside and hydrophilic phosphate heads placed outwards.

Image 5: The structure of the cell membrane (Cell membrane - Wikipedia 2008) The movement of substances across the cell can be either passive transport which requires no energy or active transport which requires energy for transport of molecules. There are many different transport mechanisms which are used by the membrane to transport molecules and are determined on the concentration, size and their charge. For example, water can diffuse through the cell membrane. However large and charged molecules cannot take place through simple diffusion, the charged molecules need to be transported through passive transport by electro chemical gradient, they move through a high concentration to a low concentration which involves proteins but no energy is required. (BBC Bitesize, page 2)

I mage6:Act i veandpassi vet r anspor t .

Passive transport can be made possible by carrier proteins which transport specific molecules such as amino acids down concentration gradients without using energy. In Passive transport the channels create water-filled pores and generate a hydrophilic path that allows ions to move through hydrophobic membrane. The channels allow downhill movement of ions, down an electrochemical gradient. The amino acids lining the pores are hydrophilic and the charge control positive or negative ions pass through for example Ca2+ is positive so the amino acids lining the pore would carry a negative charge. (Khan Academy.Org, Simple diffusion and passive transport, 2020) Active transport moves molecules against a concentration gradient and move from a low concentration to a high concentration, which requires energy and is gained from ATP (adenosine triphosphate) hydrolysis from light or electro chemical gradient of an ion for example Na+ or H+ from the same transport mechanism. An example of active transport is that it transfers small molecules through the membrane. A large particle cannot pass through the membrane, even with energy supplied by the cell. (CK-12.org, 2020). Secondary active transport requires an ion electrochemical gradient to push the uphill transport of another solute. Since the concentration of Na+ is higher outside the cell and inside the cell it is negatively charged therefore allowing the Na+ to travel down the electrochemical gradient, the transporters can move the glucose uphill, against its electrochemical gradient known as symport where both types of molecule or ion travel across the membrane in the same direction. Antiport is a method in which the two molecules are transported in the opposite directions against the electrochemical gradient.

Image 7: Symport and Antiport

Endocytosis is the process where cells absorb molecules by engulfing them in the vesicle, these can be nutrient which are needed to support the cell or pathogens that immune cells absorb and destroy. Endocytosis need energy and is a form of active transport, there are two types phagocytosis known as ‘cell eating’ and is how cells engulf and destroy microorganisms and pinocytosis the cells take is molecules from the outside which it requires to function such as water and nutrients. (Thoughtco.com, what is endocytosis, 2020)

Image 8: Endocytosis (Endocytosis - Wikipedia) Exocytosis is the process by which cells move materials from within the cell into the extracellular fluid. Exocytosis takes place when a vesicle merges with the plasma membrane, allowing its contents to be released outside the cell. The function of Exocytosis is to remove toxins or waste products from the cells interior to maintain homeostasis. For example, in aerobic respiration, cells produce the waste products carbon dioxide and water during ATP and then removed from these cells via exocytosis. Cells create signalling molecules like hormones and neurotransmitters. They are delivered to other cells following their release from the cells. When cells absorb materials from outside the cell during endocytosis, they use lipids and proteins from the plasma membrane to create vesicles. When certain exocytotic vesicles fuse with the cellular membrane, they fill the cell membrane with these materials. (thoughtco.com, what is excocytosis 2020)

Image 9: Exocytosis (Endocytosis and Exocytosis: Differences and Similarities | Technology Networks 2020) All living cells need an energy source for growth, movement, maintaining homeostasis and their involvement in cell division. The cells release the energy stored in food molecules through a method called oxidation reactions. Oxidation is a chemical reaction where electrons are moved from one molecule to another. Simultaneously the electron acceptors molecules store some energy which is released form food molecules during oxidation reactions. Cells do

not use the energy from an oxidation reaction as soon as it is released, instead is it broken down into small molecules such as ATP and nicotinamide adenine dinucleotide (NADH), which can be used for metabolism and produce cellular components.

. Image 10: An ATP molecule (An ATP molecule | Learn Science at Scitable (nature.com)) ATP is formed of an adenosine base, a ribose sugar and a phosphate chain. The high-energy phosphate bond in the phosphate chain is the key to ATP's energy storage potential. The first process in the eukaryotic energy pathway is called glycolysis where molecules of glucose are split and changed to two molecules called pyruvate and each glucose is made up of six carbon atoms and each pyruvate include three carbons. Glycolysis has ten chemical reactions including two ATP molecules which is used to produce four ATP molecules this results in glycolysis gaining Two ATP molecules in addition two NADH molecules are also yielded and are used as electron carriers. Glycolysis take place in the cytoplasm and does not require oxygen. When oxygen is present the pyruvate formed from glycolysis move from cytoplasm to the mitochondria where it is turned into Acetyl CoA (energy carrier) and another Acetyl CoA attaches to oxygen forming carbon dioxide and NADH is also produced. (Cell Energy, Cell Functions | Learn Science at Scitable (nature.com) 2010)

Image 11: Metabolism in a eukaryotic cell: Glycolysis, the citric acid cycle, and oxidative phosphorylation The electron transport chain takes place in the mitochondria inner membrane and requires several proteins the process is called oxidative phosphorylation which transports electrons found in NADH and FADH2 through the membrane proteins and oxygen which then forms water. The role of nucleic acids in the nucleus and cytoplasm.

Nucleic acids are macromolecules and provide genetic information, they are long molecules formed of linked units called nucleotides. Nucleotides are formed of a phosphoric acid, Pentose sugar (5-carbon molecules which include two types called ribose and deoxyribose) and nitrogenous base which are made up of nitrogen consisting of 5 bases called adenine, guanine, cyrosine, thymine and uracil. Nucleic acids are of two types called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is a double stranded polymer of nucleotides in the nucleus. The bases of DNA are adenine (A), guanine (G), thymine (T) and cytosine (C). DNA is broken down into chromosomes which provide instruction for protein synthesis. RNA is involved in protein synthesis and is a single stranded polymer found in the cytoplasm. The bases of RNA are cytosine (C), adening (A), guaning (G) and uracil (U). There are three types called messenger RNA (mRNA) which communicates with the cell, ribosomal RNA (rRNA) part of the ribosomes at the site of protein synthesis and transfer RNa (tRNA) that carries amino acids to the site where protein synthesis takes place. (DNA vs. RNA – 5 Key Differences and Comparison | Technology Networks)

Image 12: DNA and RNA structure (Mackenzie, 2020)

Image 13: Nucleotide structure

Protein synthesis Proteins are molecules made up of one or more chains of amino acids which are linked together by peptide binds. The proteins are small molecules in a specific order which is determined by the base sequence of nucleotides in the DNA coding for the protein. Peptide bonds are formed by removal of water molecules and joins an amino group to the carboxyl group of another.

Image 14: The relationship between amino acid side chains and proteins

Image 15: Four levels of Protein Structure Protein synthesis take place in the nucleus, it occurs in three stages which are: Transcription takes place in the nucleus where the DNA unwinds and one of the DNA strands pairs up with RNA nucleotides and eventually forms mRNA which leaves the nucleus and travels to the ribosomes. Activation is the process which takes place in the cytoplasm, a specific enzyme controls the binding of amino acids to tRNA and 3 bases are left unpaired at the end of tRNA known as codon, there are 64 different tRNAs Translation takes place in the cytoplasm. In translation the mRNA binds with a subunit of the ribosomes which reads the codons in mRNA and then tRNA with an exposed codon forms hydrogen bonds. The tRNA then forms methionine and another tRNA binds with the next codon and an amino acid binds with the methionine. This process continues until a codon cannot form a hydrogen bond with a tRNA. After translation the polypeptide chain folds into a correct shape and becomes a protein. (Khanacademy.org, the stages of translation, 2020) The generation of specialised tissues from embryonic stem cells. Stem cells are defined as a cell which can turn into specialised cell types in the human body. They can divide and produce more cells and have the ability of self-renewal. They are found in the embryo and can replace destroyed or lost cells. In adults the stem cells are found in the tissues. Embryonic stem cells are produced from undifferentiated cells found in embryos. They are found in the inner cell mass of blastocysts. There are of two types Trophectoderm which forms the placenta and provides support to the embryo and grows is the uterus. It is the outer layer of the cell. The other is the inner cell mass which is known as undifferentiated and unspecialised. These can multiply and produce other types of cells and are known as pluripotent as they can produce cells needed for the body. (Embryonic Stem Cells | stemcells.nih.gov) The process of interphase and factors that initiate cell division, and their importance. During interphase, the cell will go through a growth processes and prepare for cell division. There are three stages of interphase which are:  G1 where the cell grows  S phase where the DNA replicates

G2 where cell prepares for a second growth and prepared for cell division and the mitochondria will replicate and continue to grow until the start of mitosis. (Khan academy 2017) 

Image 16: Stages of interphase and the cell cycle.

Mitosis is used to produce daughter cells which are identical to the parent cells. The cell replicates its chromosomes which then split and each daughter cell has an identical copy of chromosomes.

 Image 17: The phases of mitosis (The Cell Cycle, Mitosis and Meiosis — University of Leicester)   

Compare and contrast cancer cells with normal cells. Cancer cells are a mutation of normal cells or damaged because of abnormalities. Cancer cells are normally present in the body but the immune system recognises them and destroys the cells. Normal cells in the body can reproduce and repair themselves. When required and can remove damaged cells in the body a process called apoptosis. Cancer cells are different from normal cells as they can replicate and don’t stop growing and eventually form a tumour which grows and unlike normal cells they ignore the signal to self-destruct.

 

 

Imade 18: Normal cell compared to cancer cells (cancer research uk.org, cancer cells, 2020)

REFERENCES  ht t ps : / / www. al l about t hej our ney . or g/ c el l s t r uc t ur e. ht m    https://assets.cambridge.org/97805216/80547/excerpt/9780521680547_excerp t.pdf  https://training.seer.cancer.gov/anatomy/cells_tissues_membranes/cells/structu re.html  https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/12    ultrastructure-of-cells/prokaryotic-cells.html    https://microbiologynote.com/prokaryotic-cell-and-eukaryotic-cell/        https://britannica.com/science/plant-cell         https://en.wikipedia.org/wiki/File:Cell_membrane_detailed_diagram_4.svg  Biological membranes (nih.gov)  Berman H.M., Coimbatore Narayanan B., Di Costanzo L., Dutta S., Ghosh S., Hudson B.P., Lawson C.L., Peisach E., Prlić A, Rose P.W., et al. Trendspotting in the Protein Data Bank. FEBS Lett. 2013;587:1036–1045. [PMC free article] [PubMed] [Google Scholar]  Blobel G., Dobberstein B. Transfer of proteins across membranes. 1. Presence of proteolytically processed and unprocessed nascent immunoglobulin light chains on membrane-bound ribosomes of murine myeloma. J. Cell Biol. 1975;67:835–851. [PMC free article] [PubMed] [Google Scholar]  http://thebiologyprimer.com/diffusion-and-osmosis  ATP Production Pathways. Provided by: Wikimedia. Located at: commons.wikimedia.org/wiki commons.wikimedia.org/wiki/File:A /File:A /File:ATP_Production_P TP_Production_P TP_Production_Pathwa athwa athways.jpg ys.jpg . License: CC BY BY:: At Attribution tribution  adenosine triphosphate. Provided by: Wikipedia. Located BY-SA: -SA: at: en.Wikipedia.org/wiki en.Wikipedia.org/wiki/adenosine%20triphosphate /adenosine%20triphosphate. License: CC BY Attribu Attribution-ShareAlik tion-ShareAlik tion-ShareAlike e  OpenStax College, Biology. October 17, 2013. Provided by: O...