Supplement: Cell Biology

PSYC 2: Biological Foundations - Fall 2012 - Professor Claffey

This document is meant to help review some key concepts from cell biology for those who want a refresher.

Cell Parts

DNA - DNA is the genetic code of the cell. It is made up of long molecules made of four different kind of molecules called base pairs. Different sequences of base pairs code for different proteins that the cell can produce. All cells in a organism contain identical DNA, but cells can be different because there are factors that control which proteins are actually made. The process of making proteins is called gene expression (the DNA codes for genes, and expression means taking them from the DNA plans and making actual proteins).

Nucleus - The nucleus is where the DNA is located. Copies of the DNA, called RNA, are made and it is these copies that leave the nucleus so that proteins can be made.

Membrane - Almost all cells have a lipid bilayer membrane. Lipid refers to the molecules that make up the membrane; lipids are a kind of fat molecule. Bilayer refers to the fact that the lipids are arranged in two symmetrical layers. Unlike water, the fatty lipid molecules do not mix well with molecules that have a charge (ions) or molecules that dissolve well in water. This is how the membrane isolated the internal contents of the cell from the extracellular fluid.

Organelles - meaning little organs, these are structures within a cell that carry out cell functioning, maintenance, cleanup, etc

Ribosomes - a kind of organelle that uses RNA to make proteins

Mitochondria - a kind of organelle that uses the fuel of the cell - glucose and oxygen - and produces an energy molecule called ATP (see below)


Concentration - When you dissolve a chemical in a liquid, concentration refers to how many atoms or molecules of that chemical are dissolved into a given volume of liquid. mM is a unit of concentration that stands for millimolar. Just as a millimeter is 1/1,000th of a meter, a millimolar is 1/1,000th of a molar. A molar is a count of the number of atoms/molecules in one liter of liquid. In this class, the units only important in terms of understanding the relative differences in concentration (e.g. for two containers that are the same size, a container with 10 mM of Na+ has more sodium ions than a container  with 1 mM, but it isn't necessary to understand exactly how much these each are)

Diffusion - atoms/molecules are constantly moving in unpredictable ways, like cats. If you put a bunch of cats in one corner of a room and ask them to stay, they will eventually spread out. Atoms/molecules do the same thing. This produces the effect the atoms/molecules will move from an area of high concentration to an area of low concentration without requiring any additional energy. When they are evenly distributed, the atoms/molecules are still moving randomly, but an equilibrium has been reached.

Ions - an ion is an atom (like sodium, potassium, chloride) that has an unequal number of protons and electrons. Because of this imbalance, it has either a positive or negative charge. Ions with like charges will repel away from one anther; ions with opposite charges attract.


Amino acids - Amino acids are a class of molecules that are important to living beings (therefore "organic chemistry"). They are combined to make proteins. Human bodies deal with 20 amino acids. Examples include tryptophan (in turkey) and glutamate (also a neurotransmitter).

Each amino acid molecule has two different ends that allow them to connect up in large chains. All amino acids have the two ends for connecting in a chain, but they each differ in what additional atoms come off the side. When a cell strings together a long chain of amino acids, these side molecules attract one another and cause the chain to crumble in on itself in a predictable way. This crumbling gives each protein its distinct shape/structure, and the structure determines what function the protein will have.

Proteins - Because there is an almost limitless number of combinations of amino acids chains and therefore protein shapes, proteins have the ability to fill many different functions in a cell. That can make up the organelles, be enzymes that cause or inhibit metabolic reactions, embedded themselves in membranes and serve as channels or receptors.

ATP - ATP is like the energy currency of a cell. ATP stands for adenosine triphosphate, meaning an adenosine molecule with 3 phosphates attached. This is a high energy form of the molecule, meaning it "wants" to split off a protein to become adenosine diphosphate (ADP). In the process of kicking off the phosphate, that energy can be used to do work and cause molecular reactions that would not happen otherwise (like the NaK pump working against concentration gradients). ATP is produced in the mitochondria by burning glucose with oxygen.

Copyright 2012 - Michael Claffey