Core Concepts Flashcards
(20 cards)
Define endocytosis and exocytosis across the cell membrane.
. Endocytosis:
. Includes phagocytosis - absorption of solid material into the cell across the cell membrane.
. And pinocytosis - absorption of liquids into the cell across the cell membrane.
. Exocytosis - excretion of material held in vesicles from the cell across the cell membrane.
Describe the process of phagocytosis.
. Involves bulk transport of solid materials into the cell - the phagocyte.
. These materials are too large to diffuse or be actively transported across the cell membrane.
. Receptors on the cell membrane bind to antigens on a bacterium, for example, and the cell membrane invaginates.
. The bacterium is absorbed into the cell via endocytosis, and a transport vesicle forms around it.
. This is known as a phagosome.
. A lysosome binds to the phagosome, forming a phagolysosome.
. The lysosome secretes digestive enzymes which hydrolyse the bacterium contained within the phagolysosome.
. The phagolysosome binds to the cell membrane and products are released via exocytosis, or remain within the cell to be presented on the cell membrane as antigens, for example.
Describe the role and structure of the cell membrane.
. Partially permeable - regulates transport of materials on and out of the cell.
. Separates the cytoplasm of the cell from the outside environment.
. Contains antigens, which enables recognition from other cells and the triggering of an immune response.
. Contains specific receptors to enable hormones, for example, to bind.
. Internal membranes separate cell organelles from the cytoplasm.
. Chemical reactions can occur on membranes e.g - aerobic respiration occurs in the inner mitochondrial membrane.
. The fluid mosaic model:
. Phospholipids that form the phospholipid bilayer, move around each other, giving the membrane fluidity.
. The phosphate head is hydrophilic and interacts with water entering the cell or outside of the cell.
. The phospholipid tails are hydrophobic, so point away from water and allow lipid soluble molecules across the cell membrane.
. Proteins embedded within the membrane vary in shape, size, and pattern, alike to a mosaic.
. Contains extrinsic proteins on one side of the bilayer. Extrinsic proteins provide structural support, and form recognition sites and receptor sites.
. And intrinsic proteins, which span across the bilayer. Include channel proteins and carrier proteins, which allow water and water soluble molecules in and out of the cell without coming into contact with hydrophobic fatty acid tails.
. Contains cholesterol, which provides the membrane with stability by fitting in between fatty acid tails.
. Contains glycoproteins, made up of proteins and carbohydrates, and glycolipids, made up of phospholipids and carbohydrates. These allow for cell to cell communication and identification.
Describe the effect of heat on the phospholipid membrane.
. The fluidity and permeability of the membrane increases, as molecules within the membrane gain more kinetic energy and move about more.
. Fluid may leak out of the membrane e.g - fluid within the vacuole of a plant cell.
Describe facilitated diffusion, including co-transport, and active uptake across the membrane.
Facilitated diffusion:
. The passive movement of molecules or ions across the membrane via transport proteins.
. Transport proteins include carrier and channel proteins.
. Channel proteins are hydrophilic, containing pores lined with polar groups to allow specific water soluble ions through the membrane.
. Carrier proteins allow for diffusion of large polar molecules across the membrane. The specific molecule e.g - an amino acid, will attach to the protein’s binding site, causing the structure of the protein to change and release the molecule through the membrane.
. Facilitated diffusion also occurs in co-transport of molecules or ions across the membrane:
. E.g - Sodium, Glucose co-transport:
. 1 glucose molecule and 2 sodium ions are co-transported across the cell membrane through a carrier protein via facilitated diffusion.
. The carrier protein releases the glucose molecule and 2 sodium ions into the cytoplasm, where they diffuse across the cell down a concentration gradient produced by glucose molecules and sodium ions moving in the blood in capillaries.
. The glucose molecule diffuses into the blood down the concentration gradient via facilitated diffusion.
. The 2 sodium ions are actively transported into the blood through a carrier protein.
. Active uptake:
. Allows for transport of large, non polar molecules or ions across the membrane against a concentration gradient.
. The molecule will attach to the binding site of a carrier protein on the outside of the membrane.
. A phosphate group will be transferred by ATP to the carrier protein in the inside of the membrane.
. The carrier protein will use energy released to change structure to accommodate the molecule through the membrane.
. The phosphate group will recombine with ADP to form ATP.
Describe the structure and function of DNA and RNA.
Structure:
. Nucleic acids:
. DNA - deoxyribonucleic acid
. RNA - ribonucleic acid.
. Nucleic acids are polymers made up of nucleotide monomers.
. Nucleotides contain a 5 carbon pentose sugar (ribose or deoxyribose), a phosphate group and an organic nitrogenous base.
. DNA nitrogenous bases include cytosine, guanine, adenine and thymine.
. RNA has uracil in place of thymine in DNA.
. Nitrogenous bases are joined through hydrogen bonds, which join the two strands of DNA together. The two strands run anti parallel to each other in the double helix. One from 5 prime to 3 prime and the other 3 prime to 5 prime.
. A condensation reaction forms between the pentose sugar of one nucleotide and the phosphate group of another nucleotide to form each strand. This forms phosphodiester bonds between nucleotides that makes up the sugar-phosphate backbone of DNA.
. RNA is a single stranded polymer.
Function:
. The base sequence in a gene determines the genetic code for the formation of a specific protein.
. A triplet of nucleotide bases determines the production of a specific amino acid in the cytoplasm of the cell.
. Therefore base sequence in DNA determines the sequence of amino acids in a protein and therefore the protein produced.
. DNA also replicates to form new cells.
. There are 3 types of RNA involved in protein synthesis - transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA). m
Describe the structure and function of ATP and ADP, and advantages of using ATP as a source of energy as opposed to glucose.
Structure:
. Both are nucleotides.
. ATP - adenosine triphosphate:
. Made up of the ribose pentose sugar and the nitrogenous base adenine (adenosine), and three phosphate groups (triphosphate).
. ADP - adenosine diphosphate, in contrast only contains two phosphate groups.
Function:
. ATP is formed in an endergonic, condensation reaction - 30.6 kJ of energy is required for the phosphorylation of ADP to form ATP. This reaction is catalysed by the ATP synthase enzyme. The energy required to combine ADP and an inorganic phosphate group comes from exergonic reactions such as cell respiration.
. 30.6 kJ of energy is released in an exergonic reaction when the ATPase enzyme hydrolyses the bond between phosphate 2 and 3, to form ADP and a phosphate group. This provides energy for endergonic reactions such as active transport.
. ATP is known as the universal energy currency as it is used to provide energy for all biochemical reactions in all living organisms.
Advantages:
. Releases energy in small, usable amounts as opposed to glucose which releases energy in a large amount all at once.
. Therefore energy can be effectively directed to different biochemical reactions.
Describe semi-conservative DNA replication and how this was proven by Meselson and Stahl.
Process:
. Occurs during the interphase stage of the cell cycle.
. The DNA helix unwinds and hydrogen bonds between complimentary nucleotide bases are hydrolysed. This reaction is catalysed by the DNA helicase enzyme.
. In a condensation reaction, catalysed by DNA polymerase, new and free nucleotide bases are paired to their complimentary bases on the old strands.
. DNA ligase catalyses the condensation reaction that involves the joining of Okazaki fragments on the lagging strands.
. The result is two double stranded DNA molecules in the nucleus, so that when the cell divides, each new nucleus contains the haploid number of DNA.
Proof:
. 1st generation bacteria were grown within an environment containing only the N15 Nitrogen isotope, used N15 in the formation of their nucleotide bases and therefore DNA molecules.
. 2nd generation bacteria containing DNA made up of N15 were grown in an environment containing only N14 - original Nitrogen.
. Through semi-conservative replication, 2nd generation bacteria would synthesise new DNA molecules by combining N14 nucleotides with the original N15 nucleotides.
. When spun in a centrifuge chamber, the band of the 2nd generation bacterial DNA appeared higher up than the 1st generation N15 DNA due to the presence of N14 creating less dense DNA molecules.
. However, the 2nd generation bacterial DNA band appeared below the 3rd generation bacterial DNA band, containing a higher volume of N14 nucleotides in their DNA molecules, so were therefore less dense.
Describe the process of protein synthesis.
. Transcription:
. DNA Helicase catalyses the hydrolysis of hydrogen bonds between complimentary bases and the unwinding of the DNA molecule.
. Free, activated RNA nucleotides bind to their complimentary nucleotide base pairs on the template strand of the DNA molecule.
. This occurs through the formation of hydrogen bonds in a condensation reaction catalysed by RNA polymerase. RNA polymerase separates from the template strand when it reaches a ‘stop’ codon.
. This forms the mRNA molecule.
. mRNA nucleotide bases are complimentary to those on the template strand and therefore mRNA is a direct copy of the coding strand on the DNA molecule.
. mRNA is released through the nuclear pore of the nuclear envelope to join to a ribosome on the RER - a synthesised protein would not fit out of the nuclear pore.
. Translation:
. The small subunit of the ribosome attaches to mRNA at a ‘start’ codon, leaving the large subunit open for the attachment of two tRNA molecules.
. tRNA molecules transfer specific amino acids to the ribosome through their anticodon binding to the complimentary codon on the mRNA molecule.
. The anticodon forms a hydrogen bond with the complimentary codon.
. Once the anticodons on the tRNA molecules have bound to their complimentary codons on the mRNA molecule, the specific amino acids that they are carrying bind together through the formation of a peptide bond, catalysed by enzyme activity in the ribosome.
. This leads to the formation of a polypeptide chain as the ribosome moves along the mRNA molecule from codon to codon. This is known as elongation.
. Elongation and the synthesis of a polypeptide chain continues until a ‘stop’ codon on the mRNA molecule is reached.
. Post translational modification:
. Once the polypeptide chain leaves the ribosome on the RER, it is packaged, using membrane of the RER, into a transport vesicle, and fuses with the Golgi body where it is modified.
. Other molecules such as carbohydrates may be added to form glycoproteins, or more polypeptide chains to form a quaternary structure protein.
. The protein may remain inside of the cell e.g - as a lysosome, or leave the cell via a transport vesicle and exocytosis e.g - as an extracellular enzyme.
Describe the process of RNA splicing.
. Exons are areas of DNA that code for specific proteins.
. Introns are areas of DNA between exons that contain blocks of repeated nucleotide bases (short tandem repeats), and are therefore non-coding.
. Introns are spliced from the mRNA molecule before it leaves the nucleus.
. It is the sequence of short tandem repeats, in introns that are spliced from the mRNA molecule, that produces variation in individual DNA.
. Alternative splicing can lead to the synthesis of different proteins as different exons containing nucleotide bases are stuck together after intron splicing has occurred.
. Prokaryotic mRNA does not contain introns so does not need to be spliced, unlike eukaryotic mRNA.
Describe different types of gene mutation.
Substitution:
. Occur due to errors in DNA replication.
. Substitution mutations involve the substitution of a new nucleotide base on the mRNA molecule.
. This changes the nucleotide sequence of a codon and therefore the anticodon from which the amino acid sequence is translated.
. If the codon codes for the same amino acid this is known as a silent mutation.
. If the codon codes for a different amino acid this is known as a missense mutation.
. If the codon changes to a ‘stop’ codon this is known as a nonsense mutation.
Frameshift:
. Frameshift mutations occur through addition of a new nucleotide base on the mRNA molecule, or deletion of an existing nucleotide base.
. This changes the sequence of nucleotide bases on the mRNA molecule and therefore results in a shift in the frame from which codons are translated by the tRNA molecule, and therefore the entire amino acid sequence.
Describe the structure and function of mitochondria and chloroplasts.
. Mitochondria - rod-shaped, have a mitochondrial matrix containing enzymes, circular DNA and ribosomes. The inner mitochondrial membrane - ‘cristae’ is the site of aerobic respiration and ATP production.
. Chloroplasts - have the stroma, also containing ribosomes, circular DNA, starch granules, but also thylakoids in grana stacks, containing photosynthetic pigments e.g - chlorophyll, and acting as the site for photosynthesis.
Define tissue and organ.
. Tissue - a collection of similar cells carrying out the same function e.g - muscular tissue that contracts to cause movement.
. Organ - an aggregation of several or more tissues to carry out a specific function for the whole organism.
Describe the difference in structure between eukaryotic and prokaryotic cells.
. Prokaryotic cells, unlike eukaryotic cells, contain no distinctive membrane bound organelles e.g - a Golgi apparatus.
. In prokaryotic cells, DNA is circular and free in the cytoplasm, in the nucleoid or plasmids, which hold genes that provide antibiotic resistance.
. Bacteria contain a peptidoglycan cell wall as opposed to a cellulose cell wall as present in eukaryotic plant cells.
. Prokaryotic cells contain 70s ribosomes, whereas eukaryotic cells contain 80s ribosomes.
. Aerobic respiration in prokaryotic cells occurs within the plasma membrane as opposed to the inner mitochondrial membrane in eukaryotic cells.
. Prokaryotic cells may contain a protective outer slime capsule layer, to provide protection against WBCs, for example.
. Bacterial cells may also contain pili to transfer genetic information between bacterial cells, a flagellum to aid in movement through fluid, or a mesosome, an infold of the cell membrane to increase surface area.
Describe the cell theory of endosymbiosis.
. Prokaryotic cells invaded eukaryotic cells and established a symbiotic relationship.
. Prokaryotic cells evolved into present day mitochondria and chloroplasts, demonstrated through the fact that mitochondria and chloroplasts are the same size as prokaryotic cells, and that they contain circular DNA and 70s ribosomes.
Describe the structure of viral cells.
. Viral cells contain either DNA or RNA enclosed within a protein coat.
. They are not considered living cells due to no present cytoplasm and a sole function to reproduce.
. Some viruses have more than one protein coat or an outer lipoprotein layer to provide better protection against the host’s immune system e.g - WBCs.
Describe the difference between the induced fit and lock and key hypotheses of enzyme action.
Lock and key:
. Enzymes have a complimentary active site structure to fit a specific substrate and form an enzyme-substrate complex.
Induced fit:
. The structure of the active site changes to fit the substrate structure and form an enzyme substrate complex.
. This allows for reactive groups of the substrate and enzyme to be brought closer together and bonds of the substrate to be weakened, lowering activation energy of the reaction.
. An example being lysozyme.
Outline and describe factors effecting rate of enzyme catalysed reactions.
. Temperature:
. At low temperatures, enzyme and substrate molecules have low kinetic energy, so successful collisions are less likely to occur and few enzyme-substrate complexes are formed.
. Therefore the rate of reaction is lower.
. At the optimum temperature, the rate of reaction is highest as the most enzyme-substrate complexes are formed due to many successful collisions between the enzyme and substrate molecules.
. This is because molecules have optimum kinetic energy.
. If the temperature is too high, enzyme molecules have too much kinetic energy and vibrate too much, causing weaker H bonds within their structure to break and the enzyme molecules have too to denature.
. Therefore E-S complexes cannot be formed and rate of reaction is greatly reduced.
. pH:
. The pH of the solution alters the charge of reactive groups within the enzyme and substrate molecules.
. An overly acidic pH results in an abundance of H ions and an overly positive charge.
. An overly alkaline pH results in an abundance of OH ions and an overly negative charge.
. Both an overly alkaline and an overly acidic pH can result in enzyme denaturation.
. At an optimum pH, the reactive groups on the substrate and enzyme molecules are complimentary and E-S complexes can be formed.
. Enzyme and substrate concentration:
. A high enzyme or substrate concentration provides a higher likelihood that E-S complexes will be formed, increasing rate of reaction.
Outline biological molecules and the complimentary enzymes that break them down. Outline the products formed.
. Starch - amylase - maltose.
. Lactose - lactase - glucose and galactose.
. Sucrose - sucrase - glucose and fructose.
. Maltose - maltase - glucose and glucose.
. Lipids - lipase - 3 fatty acids and a glycerol molecule.
. Proteins - proteases - amino acids:
. Polypeptides - peptidases - dipeptides.
. Dipeptides - dipeptidases - separate amino acids.
Describe advantages and disadvantages of using immobilised enzymes in industry.
Advantages:
. Encapsulation, e.g - in alginate beads, provides enzymes with a medium containing a stable and optimum temperature and pH. Therefore enzymes can catalyse reactions optimally at extreme temperatures or pH levels.
. Enzymes are easily recovered to be used repeatedly. This reduces costs.
. Enzymes are used in biosensors as they can detect the target substrate when it is present in low concentrations. Therefore they are very accurate.
Disadvantages:
. If enzymes are encapsulated, the substrate must first fuse into the medium. This reduces the rate of reaction.
. The presence of a medium e.g - alginate gel in alginate beads, alters the structure of the elective site, reducing enzyme activity.
. Biosensors require extensive calibration before use.
