Notes to Remember for Your Biology 101 Exam

If you are preparing for a Biology 101 (Introductory Biology) exam, this is a list of the top points to make sure you are familiar with. The list is meant to be brief so if any of the points seem unfamiliar, be sure to read more on the topic either on this site, other websites, your textbook, class notes, etc.

1) All living organisms are composed of cells. The cell is the fundamental unit of life. Some organisms like humans are multicellular- made up of trillions of differientiated cells, while other living organisms like bacteria are composed of only 1 cell.

2) Eukaryotic cells (all organisms besides bacteria) have organelles within each cell that are bound by their own lipid bi-layer membrane. Examples of important organelles are the nucleus, mitochondria and chloroplast (in photosynthetic organisms).

3) Prokaryotic cells (bacteria and archaea) do not have any membrane bound organelles. They do not have a nucleus. They instead have a region where DNA is located called the nucleoid.

4) All living organisms have DNA. DNA (deoxyribonucleic acid) is the molecule that stores hereditary information. It encodes information that determines which proteins are ultimately made in the cell. This set of proteins then produces all the characteristics you can see in an organism.

5) DNA is composed of 4 different types of nucletotides: adenine (A), thymine (T), cytosine (C) and guanine (G). In humans a single cell has billions of these nucleotides which are strung together in a long line. The specific order of the nucleotides is what provides a code for specific proteins.

6) The structure of DNA is a double helix, made up of two strands of DNA. The two strands are held together by hydrogen bonds. These hydrogen bonds are between (Adenine and Thymine)- 2 hydrogen bonds; and (Cytosine and Guanine)- 3 hydrogen bonds.

7) The structure of DNA was discovered by Watson and Crick back in 1953.

8) In the DNA double helix, A always pairs with T, and C always pairs with G. This pairing allows one strand to serve as a template for the construction of a new strand during DNA replication

9) DNA replication is semi-conservative. This means that each strand can separate into single strands and then each of these strands can serve as a template for a new double stranded DNA molecule. This again is possible since A always pairs with T; and C always pairs with G.

10) The sequence of DNA can be changed by mutations. Example: ACTGACGA to ACTGACGT. Sometimes this change will cause a change in the function of the protein that it encodes. A number of these changes over time can result in an organism with different characteristics. This process of change is called evolution.

11) Evolution selects for new characteristics that help an organism survive and reproduce. In other words it selects for changes that confer a selective advantage.

12) New cells are made from already existing cells. Bacteria produce new cells through binary fission. Eukaryotic cells produce new cells through a process called Mitosis.

13) Meiosis is similar to Mitosis but it produces cells with half the genetic content (haploid). These cells are called gametes and are used for reproduction.

14) In eukaryotic reproduction two haploid gametes (one from each parent) fuse together to produce a diploid zygote which will then grow into a new living organism with charactersitics from both parents.

15) Reproduction in bacteria is less complex. The chromosome (DNA) is replicated into two copies. The cell then divides into two cells- each with one identical chromosome.

16) In eukaryotes, Mitosis is the process that produces two identical cells from one cell. This is necessary when an organism is growing or repairing damaged tissue. Mitosis requires the chromosome (DNA) to be replicated into two copies. The replication occurs just before Mitosis starts in a stage of Interphase called the S phase (Synthesis phase).

17) Mitosis is usually described as having 4 stages: Prophase, Metaphase, Anaphase and Telophase.

18) Side note: "Telo" is often used in biology to mean "the end." This can be useful for remembering things like a telomere is at the end of a chromosome. Telocentric chromsomes have their centromere located at the end of the chromosome. Also: meta is used for "middle."

19) Prophase (the first stage of Mitosis) involves the condensation of loose chromatin into condensed chromosomes. It is the same DNA molecule just given a different name depending on whether or not it is condensed into a structure that is visible under a light microscope. In prophase you also have spindle fibers attaching to the centromeres (regions of DNA on the chromosome). These spindle fibers also attach to structures called centrioles. The spindle fibers are then used by the cell to pull the chromosomes around the cell.

20) During mitosis, the two identical copies of chromsomes are called sister chromatids.

21) In Metaphase (the second stage of Mitosis) the chromosomes are all aligned in the center of the cell- or the metaphase plate (also called the equitorial plane).

22) In Anaphase the spindle fibers pull apart the sister chromatids (which are now called daughter chromosomes) and pull the identical copies towards opposite poles of the cell.

23) In Telophase the spindle fibers fall apart, the chromosomes begin to unwind into loose chromatin, the nuclear envelope develops around each new set of chromosomes and cytokinesis begins.

24) Cytokinesis is when the cell now divides into two new cells- each with a full set of chromosomes.

25) Meiosis is similar to Mitosis with a few main differences. In Prohpase of Meiosis I, homologous chromosomes (the 2 copies of the same chromosome inherited from each parent) find each other and undergo homologous recombination- literally swapping parts of segments of the chromosome. This creates versions of the chromosome that are a hybrid of each.

26) In Meiosis, the prophase, metaphase, anaphase and telophase steps repeat in Meiosis II to produce haploid gametes for reproduction. In Anaphase I the homologous chromosomes are pulled to opposite poles, in Anaphase II the sister chromatids are pulled to opposite poles.