Cell biology exam 1

Basic properties of cells

Organized and complex, use energy, respond to stimuli, reproduce, and evolve

Cells use energy for

chemical work, mechanical work, transport (osmotic) work

A mammalian red blood cell has no DNA and cannot reproduce. Is it alive?

Alive

Modern Cell Theory

1. All living organisms are made of one or more cells

2. The cell is the structural and functional unit of life

3. All cells arise from a pre-existing cell, by division

All cells arise from a pre-existing cell, by division

All cells contain hereditary in the form of DNA

All cells are basically the same in biochemical composition

Universal genetic code, shared fundamental metabolic pathways, same basic architecture for protein-making molecular machinery

All cells are ___ and must have a ___ ___.

related, common origin

The proximity of organisms on a phylogenic tree reflects ___ of characteristics (genetic distance)

similarity

Organisms from common branches have ___ characteristics

shared

In many phylogenetic trees, but not all trees, the length of branches reflects ___ ___.

Genetic distance

Biologists recognize two types of cells

Prokaryotes and eukaryotes

Prokaryotes

• No nuclei

• No membranous organelles

• Simple genome (a circular molecule of DNA)

• Smaller size

• Sterols usually absent from membranes (cell walls)

Eukaryotes

• Nucleated

• Membranous organelles

• Several DNA molecules (chromosomes, linear)

• Bigger size

• Sterols in membranes

Prokaryote domains

Bacteria and archaea

Eukaryote domains

eukarya (animals, plants, fungi, protists)

Prokaryote unicellular vs multicellular

always unicellular

Eukaryote unicellular vs multicellular

unicellular or multicellular

Prokaryote size

Smaller (1-5 mM)

Eukaryote size

Larger (10-100 mM)

Prokaryote DNA location

nucleoid region (free floating)

Eukaryote (DNA location)

Stored in nucleus

Prokaryote DNA form

circular (plasmids)

Eukaryote DNA form

Linear (chromosomes)

What did the last universal common ancestor (LUCA) look like?

Small, single-celled “prokaryote-like”

Had a cell wall and/or a membrane

Followed the central dogma of molecular biology

RNA molecules (tRNA, rRNA) provided critical analytic activity

Although derived from a single fertilized egg cell, the human body is comprised of about ___ cells

10¹³

Biological diversity between different organisms

Evolution accounts for both the diversity and unity in life on Earth

All living organisms use the same biochemical toolkit

Individual species have unique DNA sequences (genomes)

Differences in genes create lineage-specific gains, losses, and modifications

Differ in gene expression

Biological diversity within organisms

Every cell within an organism contains an identical genome

Cell differentiation: stem cells become specialized

Differential Gene Expression: only certain genes are active in each cell type

Functional diversity

Gene expression and protein synthesis

determine:

• Cell shape

• Cell function

• Complex behavior

Gene expression =

information flow

Gene

DNA sequence that encodes a RNA/protein product

Transcription

Synthesis of messenger RNA molecules (mRNA) from a DNA template

Translation

mRNA acts as a coded template to direct polypeptide synthesis

Order of gene expression

DNA → Transcription → RNA → Translation → Polypeptide

Gene Expression includes two processes

Transcription and translation

transcription takes place in

the nucleus

translation takes place in

the cytoplasm (ribosome)

Going from gene to ____

Phenotype

DNA

information storage

mRNA

information carrier

Protein

final product (phenotypes)

Universal principles of cellular organization

Hereditary genetic information is stored in a DNA code

Four basic biochemical building blocks form the major macromolecular structures of cells

Structure, catalysis, energy storage, information storage, retrieval and inheritance

Compartmentalization of Eukaryotic Cellular Organization Provides for Functional Localization and Specialization

• Separation of function for metabolic control

• Separation of environment for localized conditions

• Concentration of substrates/enzymes to enhance reaction rates and couple reactions

• There is little empty space in cells and the cytoplasm is molecularly crowded

Because organisms and cells are related, scientists tend to gather information in well-characterized

Model organisms

some model organisms include:

eukaryotes: yeast

molecular biology: bacterium

mammals, genetics: mouse

insects, genetics: fruit fly

plants: rockcress

model organisms criteria

short life cycle, abundant offspring, inexpensive, genetic variation among members

Microscopy

visualization of cells, their components and behavior

biochemistry

protein structure and function; metabolism; physiology

molecular biology

gene expression

genetics

information flow and heredity

how do we study cells?

microscopy, biochemistry, molecular biology, genetics

Light microscopy

lower resolution, live/fixed samples, specific staining of structures and components

Fluorescence microscopy

higher resolution, live and fixed samples, specific targeting of molecules by tagging/labeling and staining

Electron microscopy

highest resolution, fixed or frozen samples only, ultrastructural, specific targeting of molecules possible

nucleus

The control center of the cell that stores DNA and genetic information

mitochondria

The control center of the cell that stores DNA and genetic information

ribosomes

Tiny structures that build and assemble proteins

Endoplasmic reticulum (ER)

A transport network that helps make and process proteins and lipids (fats)

Golgi apparatus

An organelle that sorts, modifies, and packages proteins for delivery

Lysosomes

Sacs containing digestive enzymes that break down waste and old cell parts

Chloroplasts

Organelles found in plant cells that convert sunlight into food through photosynthesis

Vacuoles

Storage compartments for water, nutrients, and waste

Centrioles/centrosomes

Help organize cell division and form spindle fibers in animal cells

an inverted microscope is more appropriate for the observation of ___ cells

live

Cell wall

A rigid outer layer found in plants and fungi that provides structural support and protection

Fluorophore

A molecule that can be excited at a given wavelength to emit light at a specific wavelength

The number of ____ ____ dictates the type of chemistry an element will participate in

valence electrons

_____ shells (highest energy electron shell) is most stable with 8 electrons (octet rule)

Valence

Covalent bond

Atoms share electrons
Each atom has an octet
Atoms may share more than one electron with another atom (multiple bond order)

Nonpolar vs. Polar covalent bonds

Electronegativity is the attraction of an atom for electrons in a covalent bond
If the sharing of electrons is fairly equal: nonpolar covalent bond

If the sharing of electrons is unequal: polar covalent bond

Polar covalent bonding

Oxygen is more electronegative than hydrogen
Electrons spend more time around oxygen’s nucleus

Oxygen will have a partial negative charge

Hydrogens will have a partial positive charge

Water exhibits polar covalent bonding

Water

A polar solvent (likes to dissolve polar things), the medium of life

Water has extensive ____ ____ bonding (liquid water is extraordinarily cohesive)

intramolecular hydrogen bonding

Liquid water has an unusually high or low melting point?

High

Liquid water has an unusually high or low boiling point?

High

Liquid water has an unusually high or low heat of vaporization?

High

Liquid water has an unusually high or low specific heat?

High

Liquid water has unusually high or low surface tension?

High

Carbon and Hydrogen have similar electronegativity, and therefore, what type of bond?

Nonpolar covalent

Are electrostatic attractions covalent?

NOT covalent

Ionic bonds

Attraction between charged atoms (electron stealing)

The chemistry of life is primarily organized with ____ bonds and ____ interactions

covalent bonds and noncovalent interactions

Hydrogen bonds

Weak, primarily electrostatic interaction

Atoms must be in polar covalent bonds (C-H bonds are NOT polar and will not H-bond)
Occurs between the partially positive H atom in one molecule and the partially negative atom in another, more electronegative atom

Intermolecular forces

Hydrophobic interactions (weak noncovalent forces)

Nonpolar molecules in water

Uncharged and do not contain polar covalent bonds

Interactions between water and nonpolar molecules is energetically unfavorable

Hydrophobic interactions

Tendency of nonpolar molecules (or nonpolar regions of molecules) in a polar solvent to interact with one another

Intermolecular forces: Van der Waals Forces

Weak interatomic attraction between two uncharged atoms

Macromolecular structure

Weak noncovalent interactions

Importance of water in biological structures

Water is a polar solvent and the medium for cellular life
Capable of extensive hydrogen bonding with itself, and with the molecules suspended within

Hydrophilic

polar, easily dissolves in water

Hydrophobic

nonpolar and will not easily dissolve in water

Amphipathic

contains regions that are polar and nonpolar

Ionization of water

Water has a slight tendency to ionize (liquid water)

Free protons are immediately hydrated to form H3O+

High ionic mobility of H+ makes acid-base reactions in water very fast

In pure water at neutral pH

[H+] = [OH-] = 10^-7 M

Ion Product Constant (25 degrees C)

K_w = [H+][OH-] = 10^-14 M²

Acids, Bases, and Buffers

Acids release protons

Bases accept protons (typically releases OH-)

Amphoteric molecules can act as either acids or bases

The pH scale measures ____

acidity

pH is used to reflect the acidity or basicity (alkalinity) of solutions

pH = -log [H+]

Buffers in living systems ___ changes in pH

resist changes in pH

Buffers consist of

weak acids and bases that do not completely ionize in water