BIOL 260 - Chapter 3: The Cellular Level of Organization PDF

THE CELLULAR LEVEL OFUnless otherwise indicated, An Introduction to the Human Body Lecture Slides by Yancy Aquino for Skyline College are derivative of OpenStax A&P Instructor Resources and are licensed CC BY. ORGANIZATION...

THE CELLULAR LEVEL OFUnless otherwise indicated, An Introduction to the Human Body Lecture Slides by Yancy Aquino for Skyline College are derivative of OpenStax A&P Instructor Resources and are licensed CC BY. ORGANIZATION 1 Phospholipid Structure } A phospholipid molecule consists of a polar phosphate “head,” which is hydrophilic and a non- polar lipid “tail,” which is hydrophobic. Unsaturated fatty acids result in kinks in the hydrophobic tails. 2 } The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. } The hydrophobic tails associate with one another, forming the interior of the membrane. } The polar heads contact the fluid inside and outside of the cell. Figure 3.3 3 } The cell membrane of the cell is a phospholipid bilayer containing many different molecular components, including proteins and cholesterol, some with carbohydrate groups attached. } Two types of transport across the cell membrane: ◦ Passive and active transport Figure 3.4 4 } The structure of the lipid bilayer allows only small, non- polar substances such as oxygen and carbon dioxide to pass through the cell membrane, down their concentration gradient, by simple diffusion Figure 3.5 5 (a) Facilitated diffusion of substances crossing the cell membrane takes place with the help of proteins such as channel proteins and carrier proteins. Channel proteins are less selective than carrier proteins, and usually mildly discriminate between their cargo based on size and charge. (b) Carrier proteins are more selective, often only allowing one particular type of molecule to cross. 6 } Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient. } If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration). } In the beaker on the left, the solution on the right side of the membrane is hypertonic. Figure 3.7 7 } A hypertonic solution has a solute concentration higher than another solution. } An isotonic solution has a solute concentration equal to another solution. } A hypotonic solution has a solute concentration lower than another solution. Figure 3.8 8 } The sodium-potassium pump is found in many cell (plasma) membranes. } Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. } In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into the cell. } Active Transport Figure 3.9 9  } Endocytosis is a form of active transport in which a cell envelopes extracellular materials using its cell membrane. (a) Phagocytosis, relatively nonselective, the cell takes in a large particle. (b) Pinocytosis, the cell takes in small particles in fluid. (c) Receptor-mediated endocytosis is quite selective. When external receptors bind a specific ligand, the cell responds by endocytosing the ligand. Figure 3.10 10  } Exocytosis is much like endocytosis in reverse. } Material destined for export is packaged into a vesicle inside the cell. } The membrane of the vesicle fuses with the cell membrane, and the contents are released into the extracellular space. Figure 3.11 11 } While this image is not indicative of any one particular human cell, it is a prototypical example of a cell containing the primary organelles and internal structures. Figure 3.13 12 } (a) The ER is a winding network of thin membranous sacs found in close association with the cell nucleus. Smooth and rough endoplasmic reticula are very different in appearance and function (source: mouse tissue). } (b) Rough ER is studded with numerous ribosomes, which are sites of protein synthesis (source: mouse tissue). } (c) Smooth ER synthesizes phospholipids, steroid hormones, regulates the concentration of cellular Ca++, metabolizes some carbohydrates, and breaks down certain toxins (source: mouse tissue). Figure 3.14 13 } a) The Golgi apparatus manipulates products from the rough ER, and also produces new organelles called lysosomes. Proteins and other products of the ER are sent to the Golgi apparatus, which organizes, modifies, packages, and tags them. Some of these products are transported to other areas of the cell and some are exported from the cell through exocytosis. Enzymatic proteins are packaged as new lysosomes (or packaged and sent for fusion with existing lysosomes). } B) An electron micrograph of the Golgi apparatus. Figure 3.15 14 } The mitochondria are the energy-conversion factories of the cell. } (a) A mitochondrion is composed of two separate lipid bilayer membranes. Along the inner membrane are various molecules that work together to produce ATP, the cell’s major energy currency. } (b) An electron micrograph of mitochondria. EM 236,000. (Micrograph provided by the Regents of University of Michigan Medical School © 2012) Figure 3.16 15 } Peroxisomes are membrane-bound organelles that contain an abundance of enzymes for detoxifying harmful substances and lipid metabolism. Figure 3.17 16 } The cytoskeleton consists of ◦ (a) microtubules ◦ (b) microfilaments ◦ (c) intermediate filaments. } The cytoskeleton plays an important role in maintaining cell shape and structure, promoting cellular movement, and aiding cell division. Figure 3.18 17 } The nucleus is the control center of the cell. The nucleus of living cells contains the genetic material that determines the entire structure and function of that cell. Figure 3.19 18 } Strands of DNA are wrapped around supporting histones. } These proteins are increasingly bundled and condensed into chromatin, which is packed tightly into chromosomes when the cell is ready to divide. Figure 3.22 19 } The DNA double helix is composed of two complementary strands. } The strands are bonded together via their nitrogenous base pairs using hydrogen bonds. Figure 3.23 20 } DNA replication faithfully duplicates the entire genome of the cell. } During DNA replication, a number of different enzymes work together to pull apart the two strands so each strand can be used as a template to synthesize new complementary strands. } The two new daughter DNA molecules each contain one preexisting strand and one newly synthesized strand. } Thus, DNA replication is said to be “semiconservative.” Figure 3.24 21 } DNA holds all of genetic information necessary to build a cell’s proteins. } The nucleotide sequence of a gene is ultimately translated into an amino acid sequence of the gene’s corresponding protein. Figure 3.25 22 } In the first of the two stages of making protein from DNA, a gene on the DNA molecule is transcribed into a complementary mRNA molecule. Figure 3.26 23  } In the nucleus, a structure called a spliceosome cuts out introns (noncoding regions) within a pre-mRNA transcript and reconnects the exons. Figure 3.27 24  } During translation, the mRNA transcript is “read” by a functional complex consisting of the ribosome and tRNA molecules. } tRNAs bring the appropriate amino acids in sequence to the growing polypeptide chain by matching their anti-codons with codons on the mRNA strand. Figure 3.28 25 } Transcription within the cell nucleus produces an mRNA molecule, which is modified and then sent into the cytoplasm for translation. } The transcript is decoded into a protein with the help of a ribosome and tRNA molecules. Figure 3.29 26 Genetic Code SECOND BASE U C A G } Each three-base UUU Phe UCU UAU Tyr UGU Cys U C UUC UCC UAC UGC sequence on DNA U UUA UCA Ser UAA Stop UGA Stop A is represented by Leu UUG UCG UAG Stop UGG Trp G a codon CUU CCU CAU His CGU U C CUC CCC CAC CGC C ◦ Codon— CUA Leu CCA Pro CAA CGA Arg A complementary CUG CCG CAG Gln CGG G three-base AUU ACU AAU AGU U Asn Ser sequence on mRNA A AUC Ile ACC Thr AAC AGC C AUA ACA AAA AGA A Met or Lys Arg AUG Start ACG AAG AGG G GUU GCU GAU GGU U Asp C GUC GCC GAC GGC G Val Ala Gly GUA GCA GAA GGA A Glu GUG GCG GAG GGG G 27 } The stages of cell division oversee the separation of identical genetic material into two new nuclei, followed by the division of the cytoplasm. Figure 3.32 28