Cell Anatomy - PDF

Anatomy of a Generalized Cell In general, a cell has three main regions or parts: 1. Plasma membrane 2. Nucleus 3. Cytoplasm Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (1 of 9) Transparent barrier for cell contents Contains...

Anatomy of a Generalized Cell In general, a cell has three main regions or parts: 1. Plasma membrane 2. Nucleus 3. Cytoplasm Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (1 of 9) Transparent barrier for cell contents Contains cell contents Separates cell contents from surrounding environment Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (2 of 9) Fluid mosaic model is constructed of: – Two layers of phospholipids arranged “tail to tail” – Cholesterol and proteins scattered among the phospholipids – Sugar groups may be attached to the phospholipids, forming glycolipids Copyright © 2021 Pearson Education, Inc. All Rights Reserved Fluid Mosaic Model Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.1 Structure of the Plasma Membrane Copyright © 2021 Pearson Education, Inc. All Rights Reserved Concept Link 1 Remember, phospholipids are polar molecules: The charged end interacts with water, and the fatty acid chains do not (see Chapter 2, p. 45). It is this property of polarity that makes phospholipids a good foundation for cell membranes. Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (3 of 9) Phospholipid arrangement in the plasma membrane – Hydrophilic (“water loving”) polar “heads” are oriented on the inner and outer surfaces of the membrane – Hydrophobic (“water fearing”) nonpolar “tails” form the center (interior) of the membrane ▪ This interior makes the plasma membrane relatively impermeable to most water-soluble molecules Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (4 of 9) Role of proteins – Responsible for specialized membrane functions: ▪ Enzymes ▪ Receptors for hormones or other chemical messengers ▪ Transport as channels or carriers Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (5 of 9) Role of sugars – Glycoproteins are branched sugars attached to proteins that abut the extracellular space – Glycocalyx is the fuzzy, sticky, sugar-rich area on the cell’s surface Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (6 of 9) Cell membrane junctions – Cells are bound together in three ways: 1. Glycoproteins in the glycocalyx act as an adhesive or cellular glue 2. Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion 3. Special cell membrane junctions are formed, which vary structurally depending on their roles Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (7 of 9) Main types of cell junctions – Tight junctions ▪ Impermeable junctions ▪ Bind cells together into leakproof sheets ▪ Plasma membranes fuse like a zipper to prevent substances from passing through extracellular space between cells Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (8 of 9) Main types of cell junctions – Desmosomes ▪ Anchoring junctions, like rivets, that prevent cells from being pulled apart as a result of mechanical stress ▪ Created by buttonlike thickenings of adjacent plasma membranes Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Plasma Membrane (9 of 9) Main types of cell junctions – Gap junctions (communicating junctions) ▪ Allow communication between cells ▪ Hollow cylinders of proteins (connexons) span the width of the abutting membranes ▪ Molecules can travel directly from one cell to the next through these channels Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.2 Cell Junctions Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Nucleus (1 of 4) Control center of the cell Contains genetic material known as deoxyribonucleic acid, or DNA – DNA is needed for building proteins – DNA is necessary for cell reproduction Three regions: 1. Nuclear envelope (membrane) 2. Nucleolus 3. Chromatin Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.3a Anatomy of the Generalized Animal Cell Nucleus Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.3b Anatomy of the Generalized Animal Cell Nucleus Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Nucleus (2 of 4) Nuclear envelope (membrane) – Consists of a double membrane that bounds the nucleus – Contains nuclear pores that allow for exchange of material with the rest of the cell – Encloses the jellylike fluid called the nucleoplasm Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Nucleus (3 of 4) Nucleolus – Nucleus contains one or more dark-staining nucleoli – Sites of ribosome assembly – Ribosomes migrate into the cytoplasm through nuclear pores to serve as the site of protein synthesis Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Nucleus (4 of 4) Chromatin – Composed of DNA wound around histones (proteins) – Scattered throughout the nucleus and present when the cell is not dividing – Condenses to form dense, rodlike bodies called chromosomes when the cell divides – What is the difference between chromatin and chromosomes? Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (1 of 12) The cellular material outside the nucleus and inside the plasma membrane Site of most cellular activities Includes cytosol, inclusions, and organelles Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (2 of 12) Three major component of the cytoplasm 1. Cytosol: Fluid that suspends other elements and contains nutrients and electrolytes 2. Inclusions: Chemical substances, such as stored nutrients or cell products, that float in the cytosol 3. Organelles: Metabolic machinery of the cell that perform functions for the cell ▪ Many are membrane-bound, allowing for compartmentalization of their functions Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.4 Structure of the Generalized Cell Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (3 of 12) Mitochondria – “Powerhouses” of the cell – Mitochondrial wall consists of a double membrane with cristae on the inner membrane – Carry out reactions in which oxygen is used to break down food into ATP molecules Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (4 of 12) Ribosomes – Made of protein and ribosomal RNA – Sites of protein synthesis in the cell – Found at two locations: ▪ Free in the cytoplasm ▪ Attached to the rough endoplasmic reticulum Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (5 of 12) Endoplasmic reticulum (ER) – Fluid-filled tunnels (or canals) that carry substances within the cell – Continuous with the nuclear membrane – Two types: ▪ Rough ER ▪ Smooth ER Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (6 of 12) Endoplasmic reticulum (ER) – Rough endoplasmic reticulum ▪ Studded with ribosomes ▪ Synthesizes proteins ▪ Transport vesicles move proteins within cell ▪ Abundant in cells that make and export proteins Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.5 Synthesis and Export of a Protein by the Rough ER (1 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (7 of 12) Endoplasmic reticulum (ER) – Smooth endoplasmic reticulum ▪ Lacks ribosomes ▪ Functions in lipid metabolism ▪ Detoxification of drugs and pesticides Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (8 of 12) Golgi apparatus – Appears as a stack of flattened membranes associated with tiny vesicles – Modifies and packages proteins arriving from the rough ER via transport vesicles – Produces different types of packages ▪ Secretory vesicles (pathway 1) ▪ In-house proteins and lipids (pathway 2) ▪ Lysosomes (pathway 3) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.6 Role of the Golgi Apparatus in Packaging the Products of the Rough ER (1 of 2) Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (9 of 12) Lysosomes – Membranous “bags” that contain digestive enzymes – Enzymes can digest worn-out or nonusable cell structures – House phagocytes that dispose of bacteria and cell debris Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (10 of 12) Peroxisomes – Membranous sacs of oxidase enzymes ▪ Detoxify harmful substances such as alcohol and formaldehyde ▪ Break down free radicals (highly reactive chemicals) ▪ Free radicals are converted to hydrogen peroxide and then to water – Replicate by pinching in half or budding from the ER Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (11 of 12) Cytoskeleton – Network of protein structures that extend throughout the cytoplasm – Provides the cell with an internal framework that determines cell shape, supports organelles, and provides the machinery for intracellular transport – Three different types of elements form the cytoskeleton: 1. Microfilaments (largest) 2. Intermediate filaments 3. Microtubules (smallest) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.7 Cytoskeletal Elements Support the Cell and Help to Generate Movement Copyright © 2021 Pearson Education, Inc. All Rights Reserved The Cytoplasm (12 of 12) Centrioles – Rod-shaped bodies made of nine triplets of microtubules – Generate microtubules – Direct the formation of mitotic spindle during cell division Copyright © 2021 Pearson Education, Inc. All Rights Reserved Table 3.1 Parts of the Cell: Structure and Function (1 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Table 3.1 Parts of the Cell: Structure and Function (2 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Table 3.1 Parts of the Cell: Structure and Function (3 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Table 3.1 Parts of the Cell: Structure and Function (4 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Table 3.1 Parts of the Cell: Structure and Function (5 of 5) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Extensions Surface extensions found in some cells – Cilia move materials across the cell surface ▪ Located in the respiratory system to move mucus – Flagella propel the cell ▪ The only flagellated cell in the human body is sperm – Microvilli are tiny, fingerlike extensions of the plasma membrane ▪ Increase surface area for absorption Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (1 of 21) Solution—homogeneous mixture of two or more components – Solvent—dissolving medium present in the larger quantity; the body’s main solvent is water – Solutes—components in smaller quantities within a solution Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (2 of 21) Intracellular fluid – Nucleoplasm and cytosol – Solution containing gases, nutrients, and salts dissolved in water Extracellular fluid (interstitial fluid) – Fluid on the exterior of the cell – Contains thousands of ingredients, such as nutrients, hormones, neurotransmitters, salts, waste products Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (3 of 21) The plasma membrane is a selectively permeable barrier – Some materials can pass through, while others are excluded – For example: ▪ Nutrients can enter the cell ▪ Undesirable substances are kept out Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (4 of 21) Two basic methods of transport – Passive processes: substances are transported across the membrane without any input from the cell – Active processes: the cell provides the metabolic energy (ATP) to drive the transport process Copyright © 2021 Pearson Education, Inc. All Rights Reserved A&P Flix™: Membrane Transport https://mediaplayer.pearsoncmg.com/assets/apf-membrane-transport Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (5 of 21) Passive processes: diffusion and filtration – Diffusion ▪ Molecule movement is from high concentration to low concentration, down a concentration gradient ▪ Particles tend to distribute themselves evenly within a solution ▪ Kinetic energy (energy of motion) causes the molecules to move about randomly ▪ Size of the molecule and temperature affect the speed of diffusion Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.9 Diffusion Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (6 of 21) Molecules will move by diffusion if any of the following applies: – The molecules are small enough to pass through the membrane’s pores (channels formed by membrane proteins) – The molecules are lipid-soluble – The molecules are assisted by a membrane carrier Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (7 of 21) Types of diffusion – Simple diffusion ▪ Unassisted movement of solutes ▪ Solutes are lipid-soluble or small enough to pass through membrane pores Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.10a Diffusion Through the Plasma Membrane Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (8 of 21) Types of diffusion – Osmosis—simple diffusion of water across a selectively permeable membrane ▪ Highly polar water molecules easily cross the plasma membrane through aquaporins ▪ Water moves down its concentration gradient Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.10b Diffusion Through the Plasma Membrane Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (9 of 21) Osmosis—A Closer Look – Isotonic solutions have the same solute and water concentrations as cells; cells gain and lose water at the same rate – Hypertonic solutions contain more solutes than the cells do; water is drawn out of the cell – Hypotonic solutions contain fewer solutes (more water) than the cells do; water is drawn into the cell Copyright © 2021 Pearson Education, Inc. All Rights Reserved A Closer Look 3.1 Four Therapy and Cellular “Tonics” Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (10 of 21) Types of diffusion – Facilitated diffusion ▪ Transports lipid-insoluble substances, charged substances, and substances too large for passage through membrane pores ▪ Examples of substances that move by facilitated diffusion–glucose and chloride ions ▪ Protein membrane channels or protein molecules that act as carriers are used Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.10cd Diffusion Through the Plasma Membrane Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (11 of 21) Passive processes – Filtration ▪ Water and solutes are forced through a membrane by fluid, or hydrostatic, pressure ▪ A pressure gradient must exist that pushes solute-containing fluid (filtrate) from a high-pressure area to a lower-pressure area ▪ Filtration is critical for the kidneys to work properly Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (12 of 21) Active processes – ATP is used to move substances across a membrane – Active processes are used when: ▪ Substances are too large to travel through membrane channels ▪ The membrane may lack special protein carriers for the transport of certain substances ▪ Substances may not be lipid-soluble ▪ Substances may have to move against a concentration gradient Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (13 of 21) Active processes – Two most important types are active transport and vesicular transport – Active transport ▪ Amino acids, some sugars, and ions are transported by protein carriers known as solute pumps ▪ ATP energizes solute pumps ▪ In most cases, substances are moved against concentration (or electrical) gradients Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (14 of 21) Active transport example: sodium-potassium pump – Necessary for nerve impulses – Sodium and potassium are pumped against their concentration gradients – Sodium is transported (pumped) out of the cell – Potassium is transported (pumped) into the cell Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.11 Operation of the Sodium-Potassium Pump, a Solute Pump (1 of 4) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (15 of 21) Active processes – Vesicular transport: substances are moved across the membrane “in bulk” without actually crossing the plasma membrane directly – Types of vesicular transport ▪ Exocytosis ▪ Endocytosis – Phagocytosis – Pinocytosis Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (16 of 21) Exocytosis – Mechanism cells use to actively secrete hormones, mucus, and other products – Material is carried in a membranous sac called a vesicle that migrates to and combines with the plasma membrane – Contents of vesicle are emptied to the outside – Refer to pathway 1 in Figure 3.6 Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.6 Role of the Golgi Apparatus in Packaging the Products of the Rough ER (2 of 2) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (17 of 21) Exocytosis – Exocytosis docking process ▪ Docking proteins on the vesicles recognize plasma membrane proteins and bind with them ▪ Membranes corkscrew and fuse together Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.12a Exocytosis Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (18 of 21) Endocytosis – Extracellular substances are enclosed (engulfed) in a membranous vesicle – Vesicle detaches from the plasma membrane and moves into the cell – Once in the cell, the vesicle typically fuses with a lysosome – Contents are digested by lysosomal enzymes – In some cases, the vesicle is released by exocytosis on the opposite side of the cell Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.13a Events and Types of Endocytosis (1 of 7) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (19 of 21) Types of endocytosis 1. Phagocytosis—“cell eating” ▪ Cell engulfs large particles such as bacteria or dead body cells ▪ Pseudopods are cytoplasmic extensions that separate substances (such as bacteria or dead body cells) from external environment ▪ Phagocytosis is a protective mechanism, not a means of getting nutrients Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.13b Events and Types of Endocytosis (6 of 7) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (20 of 21) Types of endocytosis 2. Pinocytosis—“cell drinking” ▪ Cell “gulps” droplets of extracellular fluid containing dissolved proteins or fats ▪ Plasma membrane forms a pit, and edges fuse around droplet of fluid ▪ Routine activity for most cells, such as those involved in absorption (small intestine) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.13a Events and Types of Endocytosis (7 of 7) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Membrane Transport (21 of 21) Types of endocytosis 3. Receptor-mediated endocytosis ▪ Method for taking up specific target molecules ▪ Receptor proteins on the membrane surface bind only certain substances ▪ Highly selective process of taking in substances such as enzymes, some hormones, cholesterol, and iron Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.13c Events and Types of Endocytosis Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (1 of 10) Cell life cycle is a series of changes the cell experiences from the time it is formed until it divides Cell life cycle has two major periods 1. Interphase (metabolic phase) ▪ Cell grows and carries on metabolic processes ▪ Longer phase of the cell cycle 2. Cell division (mitosis) ▪ Cell reproduces itself Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (2 of 10) Preparations: DNA Replication – Genetic material is duplicated and readies a cell for division into two cells – Occurs toward the end of interphase Copyright © 2021 Pearson Education, Inc. All Rights Reserved Concept Link 2 Recall that DNA is a very complex molecule (see Chapter 2, p. 52). It is composed of building blocks called nucleotides, each consisting of a deoxyribose sugar, a phosphate group, and a nitrogen-containing base. Essentially, DNA is a double helix, a ladderlike molecule that is coiled into a spiral staircase shape. The upright parts of the DNA “ladder,” or backbone, are alternating phosphate and sugar units, and the rungs of the ladder are made of pairs of nitrogen-containing bases. Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (3 of 10) Process of DNA replication – DNA uncoils into two nucleotide chains, and each side serves as a template – Nucleotides are complementary ▪ Adenine (A) always bonds with thymine (T) ▪ Guanine (G) always bonds with cytosine (C) – For example, a TACTGC sequence on a template strand generates a new strand with the order ATGACG Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division: DNA Replication Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.14 Replication of the DNA Molecule at the End of Interphase Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (4 of 10) Events of cell division – Mitosis—division of the nucleus ▪ Results in the formation of two daughter nuclei – Cytokinesis—division of the cytoplasm ▪ Begins when mitosis is near completion ▪ Results in the formation of two daughter cells Copyright © 2021 Pearson Education, Inc. All Rights Reserved A&P Flix™: Mitosis https://mediaplayer.pearsoncmg.com/assets/apf-mitosis Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (5 of 10) Events of mitosis: prophase – Chromatin coils into chromosomes; identical strands called chromatids are held together by a centromere – Centrioles direct the assembly of a mitotic spindle – Nuclear envelope and nucleoli have broken down Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (6 of 10) Events of mitosis: metaphase – Chromosomes are aligned in the center of the cell on the metaphase plate (center of the spindle midway between the centrioles) – Straight line of chromosomes is now seen Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (7 of 10) Events of mitosis: anaphase – Centromere splits – Chromatids move slowly apart and toward the opposite ends of the cell – Anaphase is over when the chromosomes stop moving Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (8 of 10) Events of mitosis: telophase – Reverse of prophase – Chromosomes uncoil to become chromatin – Spindles break down and disappear – Nuclear envelope re-forms around chromatin – Nucleoli appear in each of the daughter nuclei Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (9 of 10) Cytokinesis – Division of the cytoplasm – Begins during late anaphase and completes during telophase – A cleavage furrow (contractile ring of microfilaments) forms to pinch the cells into two parts – Two daughter cells exist Copyright © 2021 Pearson Education, Inc. All Rights Reserved Cell Division (10 of 10) In most cases, mitosis and cytokinesis occur together In some cases, the cytoplasm is not divided – Binucleate or multinucleate cells result – Common in the liver and skeletal muscle Copyright © 2021 Pearson Education, Inc. All Rights Reserved Figure 3.15 Stages of Mitosis (1 of 7) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (1 of 10) DNA serves as a blueprint for making proteins Gene: DNA segment that carries a blueprint for building one protein or polypeptide chain Proteins have many functions – Fibrous (structural) proteins are the building materials for cells – Globular (functional) proteins can act as enzymes (biological catalysts) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (2 of 10) DNA information is coded into a sequence of bases A sequence of three bases (triplet) codes for an amino acid For example, a DNA sequence of AAA specifies the amino acid phenylalanine Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (3 of 10) The role of DNA – Most ribosomes, the manufacturing sites of proteins, are located in the cytoplasm – DNA never leaves the nucleus in interphase cells – DNA requires a decoder and a messenger to carry instructions to build proteins to ribosomes – Both the decoder and messenger functions are carried out by RNA (ribonucleic acid) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (4 of 10) How does RNA differ from DNA? – RNA is single-stranded – RNA contains ribose sugar instead of deoxyribose – RNA contains uracil (U) base instead of thymine (T) Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (5 of 10) Three varieties of RNA – Ribosomal RNA (rRNA): Helps form the ribosomes, where proteins are built – Messenger RNA (mRNA): Carries the instructions for building a protein from the nucleus to the ribosome – Transfer RNA (tRNA): Escorts appropriate amino acids to the ribosome for building the protein Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (6 of 10) Protein synthesis involves two major phases: – Transcription – Translation We will detail these two phases next Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (7 of 10) Transcription – Transfer of information from DNA’s base sequence to the complementary base sequence of mRNA – DNA is the template for transcription; mRNA is the product – Each DNA triplet corresponds to an mRNA codon – If DNA sequence is AAT-CGT-TCG, then the mRNA corresponding codons are UUA-GCA-AGC Copyright © 2021 Pearson Education, Inc. All Rights Reserved Protein Synthesis (8 of 10) Translation – Base sequence of nucleic acid is translated to an amino acid sequence; amino acids are the building blocks of proteins – Occurs in the cytoplasm and involves three major varieties of RNA Copyright © 2021 Pearson Education, Inc. All Rights Reserved