Survey of the Natural Sciences Study Guide for the DAT

General Information

This section of the Dental Admission Test (DAT) is fairly broad in coverage, as it encompasses concepts from three major undergraduate science courses in these percentages: biology (40%), general chemistry (30%), and organic chemistry (30%). It also contains the most questions of any DAT section at 100 items. You’ll need every bit of the 90 minutes allowed to thoughtfully answer all the questions. You will have access to an on-screen periodic table while you complete the general chemistry questions in this test section.

Biology

Part of the survey of natural sciences will include a biology section covering topics from cell biology to genetics to system specifics. Your knowledge of biology will be tested on questions 1 to 40. Ninety minutes will be allotted to complete the entire section.

Both general chemistry and organic chemistry involve scratch work and problem-solving, whereas the biology section provides the test-taker with shorter, recall-based questions. As such, this section is where time can be conserved relative to other portions of the Survey of the Natural Sciences section.

Cell and Molecular Biology

Cells are the basic building blocks of all living things, and the composition and specific structures dictate how the cell interacts with the environment. Cell biology covers everything from cell structures to cell processes to cellular communications and interactions. An understanding of basic cell parts and metabolic processes is fundamental to a thorough understanding of biology as a whole.

Cell Metabolism

Carbohydrates are molecules used to generate energy through cell metabolism due to the multiple \(C-H\) bonds, which are energy rich. The products of this reaction are carbon dioxide, water, and energy:

\[\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy}\]

The first step in all metabolism is glycolysis, during which adenosine triphosphate (ATP) is formed as well as the intermediates needed for other metabolic pathways.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/7-2-glycolysis

There are various pathways through which carbohydrates are broken down to generate energy. These include aerobic respiration and anaerobic respiration. Aerobic respiration includes the decarboxylation of pyruvate (A), the citric acid cycle (B), and oxidative phosphorylation (C). It generates the most energy per molecule of carbohydrate (approximately \(36\) to \(38\) ATP).

A. Pyruvate Decarboxylation

The purpose of this phase of aerobic respiration is to generate acetyl CoA, which is used as a substrate in the citric acid cycle.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/7-3-oxidation-of-pyruvate-and-the-citric-acid-cycle

B. Citric Acid Cycle

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/7-3-oxidation-of-pyruvate-and-the-citric-acid-cycle

C. Oxidative Phosphorylation

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/7-4-oxidative-phosphorylation

Anaerobic respiration, which is the process of fermentation (alcohol fermentation and lactic acid fermentation), produces less energy (\(2\) ATP) and takes place in the absence of oxygen.

Photosynthesis

During photosynthesis, sugars are made using carbon dioxide, water, and energy from sunlight:

\[6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\]

The chemical energy from the Sun is stored in molecules like ATP and nicotinamide adenine dinucleotide phosphate (NADPH), which is later used by the chloroplasts of the plant cells to produce glucose or sugar molecules.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/8-2-the-light-dependent-reaction-of-photosynthesis

Photosynthesis is composed of two types of reactions. Light-dependent reactions take place in photosystem II, where solar energy is converted to chemical energy (NADPH and ATP) by cleaving electrons from water via sunlight (pictured above). Light-independent reactions are also called the Calvin cycle (pictured below). The chemical energy from the light-dependent reactions drives the production of sugar from carbon dioxide in the light-independent reactions.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/8-1-overview-of-photosynthesis

Enzymology

Enzymes are catalysts of biological systems, meaning that they are used to speed up the reaction by decreasing the activation energy without being used up in the process of the chemical reaction. Enzymes can be activated by the binding of a substrate to the active site on the enzyme. Each active site has specificity, meaning only certain substrates can bind the active site to produce the desired result. Enzymes can be denatured if the conditions change and will not work properly. All enzymes are designed to work at a specific body condition, temperature, and pH.

The induced fit model of substrate/enzyme binding suggests that when a substrate begins to bind, there is a conformational shift that allows the enzyme to bind the rest of the substrate.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/6-5-enzymes

Cellular Processes

There are various cellular processes that take place in the cell that enable the cell to interact and communicate with its surroundings. These processes include cellular respiration, photosynthesis, cell division, DNA replication, protein synthesis, membrane transport, cell signaling, cell cycle regulation, cellular differentiation, and cellular metabolism, among others.

Membrane Transport

Membrane transport can involve both active (energy required) or passive (no energy required) processes. Active transport is required when transporting a substance from a low concentration environment to a high concentration environment and is facilitated by a transport protein. Active transport is performed by symporters, antiporters, and pumps. Symporters transport two or more molecules in the same direction across the cell membrane, while, conversely, antiporters transport molecules in opposing directions. Passive transport is the opposite, transporting a material down its concentration gradient from an area of high concentration to an area of low concentration. Passive transport types include simple diffusion, osmosis, and facilitated diffusion.

Endocytosis is the process by which the cell membrane wraps around something from the outside environment to bring it into the cell. Two specific types of endocytosis include phagocytosis, endocytosis of large molecules, and pinocytosis, endocytosis of small molecules. Exocytosis is when a vesicle of cell product is produced and fuses with the cell membrane so the contents of the vesicle are released to the extracellular environment.

Signal Transduction

Signal transduction is the process by which a cell receives a signal from the extracellular environment and passes it along to the nucleus of the cell. The cell receives signals though molecules in the cellular membrane called receptors. When the ligand binds the receptor, a cascade is induced that leads to changes in things like gene expression, protein production, growth, and cell behavior as a cellular response.

Thermodynamics

The laws of thermodynamics dictate the reactions of molecules with one another in nature. The first law states that energy in the universe is constant. The second law states that the transfer of energy requires a release of heat and that entropy, or the degree of disorder, increases in a closed system. Because entropy in a system is always increasing, organisms must use energy to maintain low entropy and homeostasis.

Mitosis

During mitosis one cell replicates into two identical daughter cells, each with a complete and identical copy of the genome of the original cell. The stages of mitosis are (1) interphase, (2) prophase, (3) metaphase, (4) anaphase, and (5) telophase. After all stages are complete, nuclear division occurs through karyokinesis followed by cell division via cytokinesis.

Interphase is the longest phase, as it is the time when chromosomes replicate to form sister chromatids attached at a centromere. Prophase is complete when centrioles move toward opposite ends of the cell and the nuclear membrane dissolves. During metaphase, spindle fibers form and attach to chromatids at a protein called a kinetochore, which guide chromosomes to align at a metaphase plate. When the sister chromatids separate and migrate to opposite poles, anaphase is complete. This is followed by telophase, in which the spindle apparatus disintegrates and a new nuclear membrane surrounds the new chromosome.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/10-2-the-cell-cycle

Meiosis

Similarly to mitosis, meiosis begins with an interphase period during which deoxyribonucleic acid (DNA) is replicated and prepared for the following cell divisions. Following the process of meiosis, differing from mitosis, the resulting daughter cells will be haploid, that is, having half of the amount of chromosomes of the parent cell.

While the steps are similar to that of mitosis, during meiosis the cell will pass through two rounds of division to arrive at the half number of chromosomes to produce cells to be used during reproduction. During prophase I, crossing over can occur, which is a transfer of genetic information between a tetrad that leads to recombinant chromosomes. This contributes to genetic diversity.

Retrieved from: https://openstax.org/books/biology-ap-courses/pages/11-1-the-process-of-meiosis

Cell Structure and Function

The cell membrane is responsible for enclosing all other organelles in the cell and is made up of a phospholipid bilayer with proteins, cholesterols, and channels scattered throughout for membrane transport. Within the cell is the nucleus, where the DNA is housed and transcription takes place. Ribosomes are found unbound throughout the cytoplasm of the cell and are where translation takes place. The mitochondria is where ATP (energy) is made within the cell so that the cell can carry out production of cell products and signal with neighboring cells and tissues.

In addition to DNA replication and protein production, a cell is also responsible for transport of materials through the organelle called the endoplasmic reticulum. The rough endoplasmic reticulum has ribosomes attached and is responsible for protein production and transport while the smooth endoplasmic reticulum is involved in metabolism and the production of lipids.

From the respective endoplasmic reticulums, cell products go to the Golgi apparatus next, where products are altered for their transport out of the cell with instructions on where the products should be delivered. Vacuoles and vesicles are utilized for storage and transport. Centrioles are vital for spindle formation during cell division through its systems of microtubules. Lysosomes are responsible for breaking down waste products within a cell. The cytoskeleton and cytoplasm are both responsible for the overall structure and motility of the cell itself.

Experimental Cell Biology

Cell biology is shaped by scientists and researchers who explore various stages of cell activity so as to make new discoveries, such as developing new therapeutics and gaining understanding of disease states. Scientists use various methods and instrumentation, including polymerase chain reaction and gene editing.

Biomolecules

Biomolecules include carbohydrates, lipids, proteins, and nucleic acids. Each of these is unique in structure and function and serves special roles. Carbohydrates are a large source of energy and structure in cells. Lipids have a large role in membrane structure and function as well as roles in energy storage and signaling. Amino acids chained together and folded into a tertiary structure compose proteins, which have a wide array of roles from providing structure to signaling and communication to enzymatic catalysis. Nucleic acids store genetic information.

Integrated Relationships

Biology represents a large interconnected web of interactions between all living things. The study of this integration includes ecological interactions of ecosystems, physiologic interactions within an individual, genetic interactions during reproduction, and developmental interactions where signaling pathways lead to growth and development.