Medical Biology Quiz for 1st Year Dentistry Students

Ministry of Higher Education & Scientific

Ashur University, College of Dentistry, Medical Biology

Cell Biology

Cell biology is a branch of biology that deals with the study of structure and function of cell organelles
Cells are classified into two types: Prokaryotes and Eukaryotes
- Prokaryotes: No true nucleus, ribosome structure is different
- Eukaryotes: Has a true nucleus, ribosome structure is different
Both Prokaryotes and Eukaryotes have DNA and Cytoplasm structure

Cell Structure

Plasma membrane: separating the cell's internal environment from the external environment
Plasma membrane is a selective barrier that regulates the flow of materials into and out of a cell
Nucleus: large organelle that contains most of a cell's DNA
- Each chromosome is associated with several proteins and contains thousands of hereditary units called genes
Cytoplasm: has two components - cytosol and organelles
- Cytosol: fluid portion of cytoplasm contains water, dissolved solutes, and suspended particles
- Organelles: several different types, each with a characteristic shape and specific functions (e.g. Mitochondria, Ribosome)

Cell Membrane

Types of integral membrane proteins:
- Ion channels: form pores or holes through which specific ions can flow
- Carriers or transporters: selectively move polar substances or ions from one side of the membrane to the other
- Receptors: serve as cellular recognition sites
- Enzymes: catalyze specific chemical reactions at the inside or outside surface of the cell
- Linkers: anchor proteins in the plasma membranes of neighboring cells to one another or to protein filaments inside and outside the cell
Membrane glycoproteins and glycolipids: serve as cell identity markers, enable cells to recognize other cells of the same kind during tissue formation
Peripheral proteins: help support the plasma membrane, anchor integral proteins, and participate in mechanical activities such as moving materials and organelles within cells

Transport Across Cell Membranes

Functions of Plasma Membrane:
- Protective barrier
- Regulate transport in and out of cell (selectively permeable)
- Allow cell recognition
- Provide anchoring sites for filaments of cytoskeleton
- Provide a binding site for enzymes
Permeable: permits the passage of substances through it
Impermeable: does not permit the passage of substances through it
Selective permeability: plasma membranes permit some substances to pass more readily than others
Membrane fluidity: allows interactions to occur within the plasma membrane, enables the movement of the membrane components responsible for cellular processes
Types of diffusion:
- Simple diffusion: substances move freely through the lipid bilayer of the plasma membrane
- Facilitated diffusion: uses transport proteins to move high to low concentration
- Osmosis: diffusion of water through a semipermeable membrane according to the concentration gradient of water across the membrane
Types of solutions:
- Isotonic solution: has the same concentration of solutes both inside and outside the cell
- Hypertonic solution: has a higher solute concentration outside the cell than inside
- Hypotonic solution: has a higher solute concentration inside the cell than outside
Active Transport: requires energy or ATP, moves materials from low to high concentration, works against concentration gradient

Immunity

Immunity: body's defense against infectious organisms and other invaders
Types of Immunity:
- Non-specific (innate) immunity: acts against each and every invader of the body
- Specific (acquired) immunity: develops during lifetime, results from exposure to antigens
Anatomical barriers:
- Skin: first barrier and first mechanism of non-specific defense
- Epithelial surfaces: form a physical barrier that is impermeable to most infectious agents
- Desquamation of skin epithelium: helps remove bacteria and other infectious agents that have adhered to the epithelial surfaces
- Presence of sebaceous glands and sweat glands: provides an environment unsuitable for the survival of microbes
- Lysozymes: have anti-bacterial properties
Non-specific immunity: second line of defense includes phagocytic white blood cells, antimicrobial proteins, and inflammatory response

Bacteria

Bacteria: prokaryotic unicellular microorganisms
Classification:
- Based on morphology: cocci, bacilli, vibrio, spirilla, tetrahedral
- Based on gram staining: gram-positive and gram-negative
Cell structure:
- Cell wall: outer covering of the cell that protects the bacterial cell and gives it shape
- Cell membrane: surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell
- Cytoplasm: gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules
- Nucleoid region: area of the cytoplasm that contains the single bacterial DNA molecule
- Plasmids: small independent pieces of DNA that often encode for traits that are advantageous but not essential to their bacterial host
Types of bacterial movement:
- Flagella: long, whip-like protrusion that aids in cellular locomotion
- Fimbriae: protein tubes that extend out from the outer membrane, facilitate the attachment of a bacterium to a surface
- Pili: similar in structure to fimbriae, but longer and present in low numbers on the bacterial cell surface, involved in the process of bacterial conjugation
Bacterial growth:
- Follows four phases: lag phase, log phase, stationary phase, decline death phase
Bacterial nutrition:
- Heterotrophic bacteria: cannot fix carbon, uses organic carbon for growth
- Autotrophic bacteria: able to make their own food, from simple substances present in its surroundings
- Chemoautotrophs: use chemical energy, take in carbon dioxide and water and convert those substances into carbohydrates and sugars
- Photoautotrophs: obtain their energy from sunlight, contain a green pigment called cyanobacteria

Genetics

Genetics: study of heredity, based on genes
Genes: structures found in every single cell that contain information about traits that an organism has or carries
Types of nucleic acid:
- DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
Functions of Nucleic Acids:
- Transmission of hereditary Characters (DNA)
- Synthesis of Proteins (RNA)
Nucleotides: building blocks of all nucleic acids### Nucleotides
Consist of three components: nitrogen-containing base, 5-carbon sugar, and phosphate group
Base can be either pyrimidine (one ring) or purine (two rings)
Sugar can be either ribose or deoxyribose

Nucleosides

Result from combination of base and sugar

Nitrogenous Bases

Organic molecules with nitrogen atom
Main function is to bond nucleic acids together
Two types: purine and pyrimidine
Purines consist of six-membered and five-membered nitrogen-containing rings
Pyrimidines have only a six-membered nitrogen-containing ring

DNA Structure and Function

Located in cell nucleus and mitochondria
Information stored as code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
Human DNA consists of approximately 3 billion bases, with over 99% being the same in all people
Can replicate itself
A always pairs with T through two hydrogen bonds, and G always pairs with C through three hydrogen bonds

RNA

Nucleotide contains nitrogenous base, ribose sugar, and phosphate
Three types: messenger RNA, ribosomal RNA, and transfer RNA
Messenger RNA is a copy of a section of DNA
Transcription is the process of copying DNA to RNA
Translation is the process of protein synthesis from RNA
Ribosomal RNA helps build protein
Transfer RNA brings the correct amino acid to the ribosome

Human Genome

Estimated to have between 20,000 and 25,000 genes

DNA Replication

Biological process of producing two identical replicas of DNA from one original DNA molecule
Occurs in all living organisms and is the basis for biological inheritance
Three steps: initiation, elongation, and termination

Mutations

Changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations
Caused by alteration of single base units in DNA, or deletion, insertion, or rearrangement of larger sections of genes or chromosomes
Classified into two major ways: hereditary and acquired mutations
Hereditary mutations are inherited from a parent and are present throughout a person's life in virtually every cell
Acquired mutations occur at some time during a person's life and are present only in certain cells, not in every cell
Acquired mutations in somatic cells cannot be passed to the next generation

Genetic Dental Abnormalities

Examples include clefting of the lip and palate, malocclusion, periodontal disease, and oral cancer
Malocclusion is caused by crowded, extra or missing teeth, or jaws out of alignment
Periodontal disease is a bacterial infection and inflammation causing damage to soft and hard tissues supporting the teeth
Oral cancer can be caused by mutation in an oncogene or tumor suppressor gene