Cell biology Flashcards
The cell is made up of…
Phospholipid molecules makeup the basic component of cell membranes.
Hydrophilic Head
Phosphate & Glycerol
Negatively charged
Hydrophobic Tail
Fatty acids
Nonpolar
Describe the phospholipid is bilayyer and what it enables
Phosphate groups are hydrophili and arrange adjacent to Intracellular (ICF) or Extracellular (ECF) fluid.
Fatty acid tails makeup the inner membrane creating a hydrophobic or fluid free environment.
These physiochemical properties enable a fluid membrane structure
Because the phosphate groups are polar and hydrophilic, they are….
attracted to water in either the intracellular fluid. Intracellular fluid (ICF) or Extracellular fluid (ECF).
Because the lipid tails are hydrophobic, they meet in
the inner region of the membrane, excluding watery intracellular and extracellular fluid from this space.
Integral Proteins
Run through membrane bilayer.
Channel proteans
receptor proteins
glycoproteins
Channel proteins
Proteins that recognise external signals, such as receptor proteins, and in turn induce signalling changes within the cell
glycoproteins with associated bound carbohydrates….
enable cell recognition.
Peripheral Proteins
These are attached to the internal or external layer of the cell membrane, and are usually associated with receptor proteins to influence cell signalling.
concentration gradient
is the difference in concentration of a substance across a space. Molecules (or ions) will spread/diffuse from where they are more concentrated to where they are less concentrated until they are equally distributed in that space. (When molecules move in this way, they are said to move down their concentration gradient.)
Diffusion
is the movement of particles from an area of higher concentration to an area of lower concentration. A couple of common examples will help to illustrate this concept..
Molecules diffuse across the cell membrane at a rate dependant on
Concentration
Size
Charge
What molecules can cross the phospholipid bilayer
. Very small polar molecules, such as water, can cross via simple diffusion due to their small size.
Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer
Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are
repelled by the hydrophobic tails in the interior of the phospholipid bilayer.
Molecules needed by the cell that are charged or too large cross via
Channel Proteins
Carrier Proteins
Facilitated diffusion
is the diffusion process used for those substances that cannot cross the lipid bilayer due to their size, charge, and/or polarity.
A common example of facilitated diffusion is the movement of glucose into the cell, where it is used to make ATP. Although glucose can be more concentrated outside of a cell, it cannot cross the lipid bilayer via simple diffusion because it is both large and polar. To resolve this, a specialized carrier protein called the glucose transporter will transfer glucose molecules into the cell to facilitate its inward diffusion.
active transport
Where a molecule needs to move against it’s concentration gradient it requires a form of active transport, where energy is used to overcome opposite electrochemical gradients.
sodium-potassium pump
transports sodium out of a cell while moving potassium into the cell. The Na+/K+ pump is an important ion pump found in the membranes of many types of cells. These pumps are particularly abundant in nerve cells, which are constantly pumping out sodium ions and pulling in potassium ions to maintain an electrical gradient across their cell membranes. An electrical gradient is a difference in electrical charge across a space. In the case of nerve cells, for example, the electrical gradient exists between the inside and outside of the cell, with the inside being negatively-charged (at around -70 mV) relative to the outside. The negative electrical gradient is maintained because each Na+/K+ pump moves three Na+ ions out of the cell and two K+ ions into the cell for each ATP molecule that is used.
Name some examples of Vesicular driven active absorption of large extracellular molecules or particles:
Phagocytosis
Pinocytosis
Receptor-mediated Endocytosis
Endocytosis
the process of a cell ingesting material by enveloping it in a portion of its cell membrane, and then pinching off that portion of membrane. Once pinched off, the portion of membrane and its contents becomes an independent, intracellular vesicle.
Phagocytosis
(“cell eating”) is the endocytosis of large particles. Many immune cells engage in phagocytosis of invading pathogens, such as invading bacterial cells, phagocytize them, and digest them.
pinocytosis
(“cell drinking”) brings fluid containing dissolved substances into a cell through membrane vesicles.
Receptor-mediated endocytosis
is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance. Once the surface receptors have bound sufficient amounts of the specific substance (the receptor’s ligand), the cell will endocytose the part of the cell membrane containing the receptor-ligand complexes.
What is an example of receptor-mediated endocytosis
Iron, a required component of hemoglobin, is endocytosed by red blood cells in this way. Iron is bound to a protein called transferrin in the blood. Specific transferrin receptors on red blood cell surfaces bind the iron-transferrin molecules, and the cell endocytoses the receptor-ligand complexes.
exocytosis
(taking “out of the cell”) is the process of a cell exporting material using vesicular transport. Many cells manufacture substances that must be secreted. These substances are typically packaged into membrane-bound vesicles within the cell. When the vesicle membrane fuses with the cell membrane, the vesicle releases it contents into the interstitial fluid. The vesicle membrane then becomes part of the cell membrane.
Cells of the stomach and pancreas produce and secrete digestive enzymes through exocytosis. Endocrine cells produce and secrete hormones that are sent throughout the body, and certain immune cells produce and secrete large amounts of histamine, a chemical important for immune responses.
The Endoplasmic Reticulum is responsible for:
Protein synthesis
Lysosome formation
Vesicle formation
Lipid synthesis
The endomembrane system is responsible for
protein and lipid synthesis, and cellular packaging.
The endomembrane system is responsible for protein and lipid synthesis, and cellular packaging.
It comprises of the:
Endoplasmic reticulum
Golgi apparatus
Vesicles
There are three major components of the endoplasmic reticulum:
Rough ER & Ribosomes
Smooth ER
endoplasmic reticulum (ER)
is a system of channels that is continuous with the nuclear membrane (or “envelope”) covering the nucleus and composed of the same lipid bilayer material. The ER can be thought of as a series of winding thoroughfares. The ER provides passages throughout much of the cell that function in transporting, synthesizing, and storing materials. The winding structure of the ER results in a large membranous surface area that supports its many functions.
The Golgi apparatus Packages proteins from the rough ER and directs transport either:
Intracellular
Targeted through cytoskeleton network.
Extracellular
Excreted from the cell via exocytosis
Golgi apparatus
responsible for sorting, modifying, and shipping off the products that come from the rough ER, much like a post-office. The Golgi apparatus looks like stacked flattened discs, almost like stacks of oddly shaped pancakes. Like the ER, these discs are membranous. The Golgi apparatus has two distinct sides, each with a different role. One side of the apparatus receives products in vesicles. These products are sorted through the apparatus, and then they are released from the opposite side after being repackaged into new vesicles. If the product is to be exported from the cell, the vesicle migrates to the cell surface and fuses to the cell membrane, and the cargo is secreted.
mitochondrion (plural = mitochondria)
is a membranous, bean-shaped organelle that is the “energy transformer” of the cell. Mitochondria consist of an outer lipid bilayer membrane as well as an additional inner lipid bilayer membrane.
The inner membrane is highly folded into winding structures with a great deal of surface area, called cristae. It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration.
These reactions convert energy stored in nutrient molecules (such as glucose) into adenosine triphosphate (ATP), which provides usable cellular energy to the cell.
cytoskeleton
is a group of fibrous proteins that provide structural support for cells, but this is only one of the functions of the cytoskeleton. Cytoskeletal components are also critical for cell motility, cell reproduction, and transportation of substances within the cell.
microtubules
A very important function of microtubules is to set the paths (somewhat like railroad tracks) along which the genetic material can be pulled (a process requiring ATP) during cell division, so that each new daughter cell receives the appropriate set of chromosomes. Two short, identical microtubule structures called centrioles are found near the nucleus of cells. A centriole can serve as the cellular origin point for microtubules extending outward as cilia or flagella or can assist with the separation of DNA during cell division. Microtubules grow out from the centrioles by adding more tubulin subunits, like adding additional links to a chain.
microfilament
is a thinner type of cytoskeletal filament. Actin, a protein that forms chains, is the primary component of these microfilaments. Actin fibers, twisted chains of actin filaments, constitute a large component of muscle tissue and, along with the protein myosin, are responsible for muscle contraction. Like microtubules, actin filaments are long chains of single subunits (called actin subunits). In muscle cells, these long actin strands, called thin filaments, are “pulled” by thick filaments of the myosin protein to contract the cell.
Actin also has an important role during cell division. When a cell is about to split in half during cell division, actin filaments work with myosin to create a cleavage furrow that eventually splits the cell down the middle, forming two new cells from the original cell.
intermediate filament
is a filament intermediate in thickness between the microtubules and microfilaments. Intermediate filaments are made up of long fibrous subunits of a protein called keratin that are wound together like the threads that compose a rope. Intermediate filaments, in concert with the microtubules, are important for maintaining cell shape and structure. Unlike the microtubules, which resist compression, intermediate filaments resist tension—the forces that pull apart cells. There are many cases in which cells are prone to tension, such as when epithelial cells of the skin are compressed, tugging them in different directions. Intermediate filaments help anchor organelles together within a cell and also link cells to other cells by forming special cell-to-cell junctions.
nuclear envelope.
This membranous covering consists of two adjacent lipid bilayers with a thin fluid space in between them. Spanning these two bilayers are nuclear pores.
nuclear pore
a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and the cytoplasm. Proteins called pore complexes lining the nuclear pores regulate the passage of materials into and out of the nucleus.
nucleolus
. There also can be a dark-staining mass often visible under a simple light microscope, called a nucleolus (plural = nucleoli). The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of ribosomes. Once synthesized, newly made ribosomal subunits exit the cell’s nucleus through the nuclear pores.
Principal components of the nucleus
Nuclear Envelope
Nucleus membrane
Nuclear Pore
Transfer channel
Nucleolus
Synthesis of RNA
DNA
A DNA molecule is made of two strands that “complement” each other in the sense that the molecules that compose the strands fit together and bind to each other, creating a double-stranded molecule that looks much like a long, twisted ladder. Each side rail of the DNA ladder is composed of alternating sugar and phosphate groups. The two sides of the ladder are not identical but are complementary. These two backbones are bonded to each other across pairs of protruding bases, each bonded pair forming one “rung,” or cross member. The four DNA bases are adenine (A), thymine (T), cytosine (C), and guanine (G). Because of their shape and charge, the two bases that compose a pair always bond together. Adenine always binds with thymine, and cytosine always binds with guanine.
Within the nucleus are threads of chromatin composed of DNA and associated proteins. Along the chromatin threads, the DNA is wrapped around a set of histone proteins. A nucleosome is a single, wrapped DNA-histone complex. Multiple nucleosomes along the entire molecule of DNA appear like a beaded necklace,
Stages of DNA replication
- Initiation
Separation of DNA - Elongation
Synthesis of complementary strands - Termination
Completion of two complementary strands
Describe stage 1 of dna replication
Stage 1: Initiation. The two complementary strands are separated, much like unzipping a zipper. Special enzymes, including helicase, untwist and separate the two strands of DNA.
Describe stage 2=of dna replication
Stage 2: Elongation. Each strand becomes a template along which a new complementary strand is built. DNA polymerase brings in the correct bases to complement the template strand, synthesizing a new strand base by base. A DNA polymerase is an enzyme that adds free nucleotides to the end of a chain of DNA, making a new double strand. This growing strand continues to be built until it has fully complemented the template strand.
Describe stage 3 of dna replication
Stage 3: Termination. Once the two original strands are bound to their own, finished, complementary strands, DNA replication is stopped and the two new identical DNA molecules are complete.
semiconservative
Each new DNA molecule contains one strand from the original molecule and one newly synthesized strand. The term for this mode of replication is “semiconservative,” because half of the original DNA molecule is conserved in each new DNA molecule. This process continues until the cell’s entire genome, the entire complement of an organism’s DNA, is replicated.
proteome
Just as the cell’s genome describes its full complement of DNA, a cell’s proteome is its full complement of proteins. Protein synthesis begins with genes.
Gene
A gene is a functional segment of DNA that provides the genetic information necessary to build a protein. Each particular gene provides the code necessary to construct a particular protein. Gene expression, which transforms the information coded in a gene to a final gene product, ultimately dictates the structure and function of a cell by determining which proteins are Therefore, a gene, which is composed of multiple triplets in a unique sequence, provides the code to build an entire protein, with multiple amino acids in the proper sequence.
triplet
a section of three DNA bases in a row that codes for a specific amino acid. Similar to the way in which the three-letter code d-o-g signals the image of a dog, the three-letter DNA base code signals the use of a particular amino acid. For example, the DNA triplet CAC (cytosine, adenine, and cytosine) specifies the amino acid valine.
Transcription
Transcription is the process by which messenger RNA copies the code for a specific gene. This occurs in the nucleus. Like all molecular mechanisms this takes place over three stages/steps:
Stage 1 of dna transcription
Stage 1: Initiation. A region at the beginning of the gene called a promoter—a particular sequence of nucleotides—triggers the start of transcription
Stage 2 of dna transcription
Stage 2: Elongation. Transcription starts when RNA polymerase unwinds the DNA segment. One strand, referred to as the coding strand, becomes the template with the genes to be coded. The polymerase then aligns the correct nucleic acid (A, C, G, or U) with its complementary base on the coding strand of DNA. RNA polymerase is an enzyme that adds new nucleotides to a growing strand of RNA. This process builds a strand of mRNA.
Stage 3 of dna transcription
Stage 3: Termination. When the polymerase has reached the end of the gene, one of three specific triplets (UAA, UAG, or UGA) codes a “stop” signal, which triggers the enzymes to terminate transcription and release the mRNA transcript.
Describe dna translation
Stages:
1. Initiation
mRNA binds to ribosome in the Rough ER.
- Elongation
tRNA with anticodon to the mRNA sequence adds its respective amino acid to the polypeptide chain - Termination
Stop region terminates translation
Describe the elongation stage of translation
The elongation stage involves the recognition of a tRNA anticodon with the next mRNA codon in the sequence. Once the anticodon and codon sequences are bound (remember, they are complementary base pairs), the tRNA presents its amino acid cargo and the growing polypeptide strand is attached to this next amino acid. This attachment takes place with the assistance of various enzymes and requires energy. The tRNA molecule then releases the mRNA strand, the mRNA strand shifts one codon over in the ribosome, and the next appropriate tRNA arrives with its matching anticodon.
Describe the termination stage of translation
This process continues until the final codon on the mRNA is reached which provides a “stop” message that signals termination of translation and triggers the release of the complete, newly synthesized protein. Thus, a gene within the DNA molecule is transcribed into mRNA, which is then translated into a protein product.
Interphase
Made up of the following sub-phases: Gap 1 (G1 Phase) Synthesis (S Phase) Gap 2 (G2 Phase) Resting (G0 Phase)
Interphase is the period of the cell cycle during which the cell is not dividing. The majority of cells are in interphase most of the time
Cell cycle
One “turn” or cycle of the cell cycle consists of two general phases: interphase, followed by mitosis and cytokinesis.
G1 phase
G1 phase (gap 1 phase) is the first gap, or growth phase in the cell cycle
cells will vary the most in their duration of the G1 phase. It is here that a cell might spend a couple of hours, or many days.
S phase
The S phase (synthesis phase) is period during which a cell replicates its DNA.
The S phase typically lasts between 8-10 hours and the G2 phase approximately 5 hours.
G2 phase
second gap phase, during which the cell continues to grow and makes the necessary preparations for mitosis.
G0
a resting phase of the cell cycle. Cells that have temporarily stopped dividing and are resting (a common condition) and cells that have permanently ceased dividing (like nerve cells) are said to be in G0.
