cell unit review

what is a cell?

• the smallest complete unit of life; able to do all the activities necessary for life

  • composed of a selectively permeable membrane that contains genetic material (DNA) and molecular machinery

    • able to grow, develop, maintain constant internal living conditions, and reproduce 

what is a tissue?

• a collection of cells and extracellular material that perform a specific function; often make up part of an organ

  • four types: muscle, connective, epithelial, nervous 

what is an organ?

• an anatomical structure containing at least two types of tissue, has recognizable boundaries, performs a specific function in the body 

what is an organ system?

• an organ or group of organs and related structures working together to provide a specific function for the body

  • integumentary, skeletal, muscular, nervous, endocrine, circulatory, respiratory, urinary, digestive, reproductive, lymphatic/immune 

what type of cell makes up the human body?

eukaryotic cells

what is an eukaryotic cell?

a complex cell that contains membrane-bound organelles and a nucleus holding a majority of the genetic material 

• exact structure of any human cell depends on its job

• cells are organized into one of the four tissue types based broadly on what they do, not how they’re built 

what is the plasma membrane made of?

the cell’s plasma membrane is made up of a double layer of phospholipids and a variety of proteins and other molecules (ex: cholesterol)

what is the plasma membrane’s main function?

to choose what enters and leaves the cell

what are the different types of membrane proteins?

receptors, enzymes, channel proteins, carrier proteins, cell identity markers, cell-adhesion molecules

what do receptors do?

receive chemical signals from outside the cell

what do enzymes do?

break down molecules

what are channel proteins and what do they do?

tunnels in the membrane that allow fluids to move in and out (passive transport)

what do cell identity markers do?

form ‘identification tags;’ distinguish cells from foreign invaders

what do carrier proteins do?

grab ahold of molecules and move them in or out (active transport)

what do cell-adhesion molecules do?

allow a cell to adhere to other cells and the extracellular matrix 

what is the extracellular matrix?

• an outside network of proteins and carbohydrates that serves many functions 

  •  forms pathways for signaling, provides dense structure, brings things in and out for homeostasis

  • varies by tissue type 

what is extracellular fluid?

• any fluid outside the plasma membrane (blood or tissue fluid)

  • made mostly of water, but also contains proteins and ions 

where is the extracellular membrane and extracellular fluid located?

outside of the cell/in between cells

what prevents cells from growing larger than they do?

• cell size is constrained by surface area to volume ratio 

  • the larger the volume of the cell, the harder it is for the membrane to transport materials in and out quickly enough

what is homeostasis?

• the ability of a body (cell or larger) to maintain constant internal conditions despite changes in the external environment

what is a negative feedback loop?

• the consequences of the action causes the action to shut off

• when a problem is fixed, it causes the response to stop

what are the four types of cytosis?

endocytosis, exocytosis, phagocytosis, pinocytosis

what is endocytosis?

• any cytosis that brings matter into cell 

what is exocytosis?

• any cytosis that expels matter from the cell 

what is phagocytosis?

• “call eating;” cell engulfs and brings in a particle 

what is pinocytosis

• “cell drinking;” cell takes in vesicles containing extracellular fluid

what is diffusion?

• the net movement of a dissolved substance from a high concentration to a low concentration 

  • happens naturally; requires no energy 

  • cells use diffusion to move materials in or out when its advantageous

what is osmosis?

• the net movement of water from high to low across a membrane 

  • membrane blocks movement of dissolved solids 

what is the sodium-potassium ion pump?

• a carrier protein 

• generates body heat

• assists in other forms of active transport

• helps cellular homeostasis

• helps nerve and muscle cells communicate 

• helps produce ATP in mitochondria

what is a hormone?

• a chemical signal that is made and released by endocrine glands; triggers a specific response in a cell that is able to receive it 

  • may be either a lipid or a protein

what are the two ways hormones operate?

• method one: chemical signal moves through cell membrane, goes directly to organelles to stimulate activity 

  • lipids (steroids) 

• method two: chemical signal binds to protein on outside of cell, protein triggers a different chemical inside the cell to complete delivery of the message 

  • protein 

  • like passing a baton

what is the difference between a first messenger and a second messenger?

• outside chemical is the first messenger, internal chemical is the second messenger (method two: protein)

what is metabolism?

• the sum of all chemical reactions in the body

  • since the body requires energy for maintenance and homeostasis, the net metabolism is described as a rate of calories burned 

what is a metabolic pathway?

• a series of linked chemical reactions occurring within the cell 

  • Often mediated by enzymes

what are metabolites?

products and intermediate stages of a chemical

what is a catabolic reaction?

• a chemical reaction that breaks down larger molecules into simpler ones 

  • frequently used by the human body to extract energy tied up in the chemical bonds of larger molecules

  • a precursor reaction to making ATP

  • example: breaking down whole grains into simple sugars during digestion

what is an anabolic reaction?

• a chemical reaction that joins smaller molecules to build larger molecules

  • stores energy

  • examples: joining fatty acid molecules together to make lipids; joining amino acids together during protein synthesis 

what is the main metabolic pathway for using sugar to make ATP in the human body (with the help of oxygen)?

• Step 1: glycolysis is a series of steps that break down sugar to produce a small amount of ATP 

  • occurs in cytoplasm

  • doesn’t require oxygen

• Step 2: krebs cycle occurs after glycolysis; products of glycolysis enter the mitochondria… 

  • electrons are extracted in a series of chemical steps

  • occurs inside mitochondria

  • requires oxygen

• Step 3: electron transport chain is initiated; large amounts of ATP made 

  • occurs inside mitochondria

  • aerobic process; oxygen is required!

  • the primary method of gaining ATP for energy, and the main reason humans must breathe oxygen

  • notice that the oxygen takes away leftover carbons, turning into carbon dioxide 

  • choarrier molecules take electrons to the ETC

how are lipids utilized for energy?

• four enzymes break down lipids in the cell’s cytoplasm and convert them to acetyl-coA…

  • acetyl-coA enters the mitochondria and goes through the Krebs Cycle

how are proteins utilized for energy?

•  proteins are first broken down into amino acids by protease enzymes…

  • amino acids may be used by the cells to build more proteins

  • amino acids may be broken down when additional enzymes remove the amino group, forming glucose and the waste urea