Chapter 3 - Cellular Level Flashcards
What is cell division?
Where one cell divides into two identical cells
What is a cell?
Living structural and functional units enclosed by a membrane
What is the name of cell biology?
Cytology - study of cellular structure and function
What are the three main parts of a cell?
- Plasma membrane
- Cytoplasm
- Nucleus
What is the plasma membrane?
The cell’s flexible outer surface, separating the cell’s internal environment from the external environment
A flexible, sturdy barrier that surrounds and contains the cytoplasm of a cell
What is cytoplasm?
All of the cellular contents between the plasma membrane and the nucleus.
Cytoplasm is divided into what two parts?
- Cytosol - the fluid portion of cytoplasm
2. Organelles - “little organs”, each type has a characteristic shape and specific function
What is the nucleus of a cell?
A large organelle that houses most of the cell’s DNA
Contains chromosomes
What is a chromosome?
A single molecule of DNA associated with several proteins
Contains thousands of hereditary units called genes that control most aspects of cellular structure and function
What is a fluid mosaic model?
The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contains a mosaic of many different proteins
What is the basic structural framework of the plasma membrane?
Lipid bilayer
What is the lipid bilayer made up of?
Back-to-back layers made up of:
- Phospholipids
- Cholesterol
- Glycolipids
What are phospholipids?
Lipids that contain phosphorus
What is a cholesterol molecule?
Steroid with an attached OH- group
What is a glycolipid?
Lipid with an attached carbohydrate group
What does amphipathic mean?
Both polar and nonpolar parts
What are integral proteins?
Proteins that extend into or through the lipid bilayer among the fatty acid tails and are firmly embedded in it
What are transmembrane proteins?
They span the entire lipid bilayer and protrude into both the cytosol and extracellular fluid
What are peripheral proteins?
Not as firmly embedded in the membrane
Attached to the polar heads of membrane lipids or to integral proteins at the inner or outer surface of the membrane
What are glycoproteins?
Proteins with carbohydrate groups attached to the ends that protrude into the extracellular fluid
What is the glycocalyx?
An extensive sugary coating on the extracellular surface of the plasma membrane. It is composed of the carbohydrate portions of the membrane, glycolipids and glycoproteins
What are the functions of the glycocalyx?
- enables cells to recognize each other
- enables cells to adhere to each other
- protects cells from being digested by enzymes in the extracellular fluid
- it is hydrophilic, attracts a film of fluid to the surface, makes it slippery
What are ion channels?
Pores or holes that specific ions (K+), can flow into and out of the cell
Most are selective, allow only one type of ion through
What is a carrier?
Transports specific substances across membrane by changing shape
Selectively moves a polar substance or ion from one side of the membrane to the other
Also known as transporters
What are receptors?
Recognizes specific ligand and alters cell’s function in some way
Serve as cellular recognition sites
Each type of receptor recognizes and binds a specific type of molecule
What is a ligand?
A specific molecule that binds to a receptor
What is an enzyme?
A catalyst to speed up specific chemical reactions inside or outside of the cell
What are linkers?
Anchor filaments inside and outside the plasma membrane
Provides structure, stability and shape
Link two cells together
What do cell-identity markers do?
- Recognize other cells of the same kind during tissue formation
- Recognize and respond to potentially dangerous foreign cells
What does a membranes fluidity depend on?
Number of double bonds in the fatty acid tails of the lipids that make up the bilayer and the amount of cholesterol present
Why is the membrane described as selectively permeable?
Allows some substances to pass more easily than others
What is the lipid bilayer permeable to?
To nonpolar, uncharged molecules
(Oxygen, carbon dioxide, steroids )
*impermeable to ions and large, uncharged polar molecules such as glucose
** slightly permeable to small uncharged polar molecules such as water, urea,
What is a concentration gradient?
The difference in the concentration of a chemical from one place to another (such as, inside to outside of a cell)
Give two examples of something that is more concentrated on the outside than inside of the cell.
Oxygen molecules Sodium ions (Na+)
Give two examples of something that is more concentrated on the inside than outside of the cell.
Carbon dioxide Potassium ions (K+)
Which surface of the membrane is more positively charged? Negatively?
Inner surface is more negatively charged
Outer surface is more positively charged
What is the electrical gradient?
The difference in electrical charges between two regions
What is the name for the electrical gradient across a plasma membrane?
Membrane potential
Why is the concentration gradient and electrical gradient important?
It helps move substances across the plasma membrane
A substance will move DOWN its concentration gradient
What is the term for the combined influence of the concentration gradient and the electrical gradient on movement of a particular ion?
Electrochemical gradient
What are passive processes?
A substance moves down its concentration/electrical gradient to cross the membrane using only its own kinetic energy
No input of energy from the cell is required
Example, diffusion
What are active processes?
Cellular energy is used to drive the substance “uphill” against its concentration/electrical gradient
Cellular energy is used (usually ATP)
What is diffusion?
The passive process in which the random mixing of particles in a solution occurs b/c of the particles kinetic energy.
What are some factors that influence the diffusion rate of substances across a plasma membrane?
Steepness of the concentration gradient, higher concentration - faster
Temperature, higher temp - faster
Mass, larger mass - slower
Surface area, more surface area - faster
Diffusion distance, greater distance - slower
What are the three different kinds of diffusion?
Simple, facilitated, osmosis
What is simple diffusion?
Passive process, which substances move freely through the lipid bilayer of the plasma membrane without the help of transport proteins
Nonpolar, hydrophobic molecules move across the lipid bilayer through the process of simple diffusion
What are some example of molecules that move by simple diffusion?
Oxygen, carbon dioxide, nitrogen, fatty acids, steroids, and fat soluble vitamins (nonpolar hydrophobic)
Water, urea, small alcohols (small uncharged polar)
What is facilitated diffusion?
An integral membrane protein assists specific substances across the membrane
Can either be a membrane channel or carrier
This is for substances that are too polar or highly charged to move by simple diffusion
What is channel-mediated facilitated diffusion?
A solute moves down a concentration gradient across the lipid bilayer through a membrane channel
Most are ion channels
Generally slower than simple diffusion
What is carrier-mediated facilitated diffusion?
A carrier (transporter) moves a solute down a concentration gradient across the plasma membrane
Passive process
Solute binds to a specific carrier on one side of the membrane and is released on the other side
What is the transport maximum?
The rate at which facilitated diffusion can occur, depends on the number of carriers available in the plasma membrane
What are some examples of substances that move across the plasma membrane by carrier-mediated facilitated diffusion?
Glucose, fructose, galactose, some vitamins
Describe how glucose enters a plasma membrane.
- Glucose binds to a specific type of carrier protein called the glucose transporter on the outer surface
- Transporter changes shape, glucose passes through the membrane
- Transporter releases glucose on the inside of the membrane
How does insulin affect the diffusion of glucose?
Insulin promotes the insertion of many copies of glucose transporters into the plasma membrane, thus increasing the rate of glucose diffusion
What is the inability to produce insulin called?
Diabetes mellitus
What is osmosis?
A type of diffusion in which there is a net movement of a solvent through a selectively permeable membrane
Passive process
Solvent is water in living systems
Moves from higher WATER concentration to lower WATER concentration
During osmosis, what are the two ways that water molecules can pass through a plasma membrane?
- By moving between neighbouring phospholipid molecules in the lipid bilayer, by simple diffusion
- By moving through aquaporins, integral membrane proteins that function as water channels
When can osmosis only occur?
When a membrane is permeable to water but not permeable to certain solutes
What is hydrostatic pressure?
The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.
What is osmotic pressure?
The minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
(Amount of pressure needed to stop the movement of water from the left tube into the right tube)
What is a solutions tonicity?
A measure of the solutions ability to change the volume of cells by altering their water content
What is an isotonic solution?
Any solution in which a cell maintains its normal shape and volume
What is a hypotonic solution?
A solution that has a lower concentration of solutes than the cytosol in the red blood cells.
Water molecules enter the the cells faster than they leave, causing the RBCs to swell and eventually burst
What is hemolysis?
When red blood cells rupture b/c they are placed in a hypotonic solution
What is lysis?
The rupture of any other cells (other than red blood cells) due to being placed in a hypotonic solution
What is a hypertonic solution?
A higher concentration of solutes than does the cytosol inside red blood cells
Water molecules move out of the cells faster than they enter, causing the cells to shrink
What is the name for when cells shrink in size due to a hypertonic solution?
Crenation
Is pure water a hypotonic or a hypertonic solution?
Very hypotonic and causes rapid hemolysis
What is active transport?
An active process where energy is required for carrier proteins to move solutes across the membrane against their concentration gradient
What are the two sources of energy that can be used to drive active transport?
- Energy obtain from hydrolysis of ATP is the source of primary active transport
- Energy stored in an ionic concentration gradient is the source in secondary active transport
What are some example of ions that are actively transported across the plasma membrane?
Na+, K+, H+, Ca+2, I-, Cl-, amino acids and monosaccharides
Describe how primary active transport works.
Energy derived from hydrolysis of ATP changes the shape of a carrier protein, which pumps a substance across a plasma membrane against its concentration gradient.
A typical body cell expends about 40% of its ATP it generates on primary active transport
What is the most prevalent primary active transport mechanism?
The sodium-potassium pump.
Expels sodium from the cells and brings in potassium
What does the sodium-potassium pump do?
Maintains a low concentration of sodium in the cytosol (against its concentration gradient) and maintains a high concentration of potassium in the cytosol (against its concentration gradient)
B/c sodium and potassium slowly leak through the membrane, the pumps must work continuously
What are the 4 steps of the sodium-potassium pump?
- Three sodium ions in the cytosol bind to the pump protein
- Binding of sodium ions triggers the hydrolysis of ATP into ADP (a reaction that attaches a phosphate group to the pump protein). This changes the shape of the protein, expelling 3 sodium ions into the ECF, now the shape favours binding of two potassium ions in the ECF to the pump protein
- Binding of potassium ions triggers the release of the phosphate group from the pump protein, this reaction again causes the pump to change shape
- As the pump reverts to its original shape, it’s releases potassium ions into the cytosol, pump is ready again to bind three sodium ions. Cycle repeats
Why is the sodium-potassium pump so important?
It is crucial for maintaining normal cell volume and for the ability of some cells to generate action potentials from electrical signals.
Helps to maintain normal tonicity on each side of the plasma membrane, ensures that cells don’t shrink or swell
What is secondary active transport?
The energy stored in a Na+ or H+ concentration gradient is used to drive other substances cross the membrane against their own concentration gradient. B/c a Na+ or H+ concentration gradient is established by primary active transport, secondary active transport INDIRECTLY uses energy obtained from the hydrolysis of ATP.
Uses the potential energy of Na+, like water stored behind a dam.
If Na+ can leak back in, stored energy can be converted to kinetic energy and bring other substances across
What is a symporter?
A carrier protein that simultaneously bind to a sodium ion and another substance and then changes shape so that both substances cross the membrane at the same time, this transporter would be called a symporter
What is an antiporter?
When two substances move in opposite directions across the membrane
What is a vesicle?
A small spherical sac
What is endocytosis?
Materials move INTO a cell in a vesicle formed from the plasma membrane
Need energy supplied by ATP
What is exocytosis?
Materials move OUT of a cell by the fusion of the vesicles formed inside the cell with the plasma membrane
Need energy supplied by ATP
What are three different kinds of endocytosis?
- Receptor-mediated endocytosis
- Phagocytosis
- Bulk-phase endocytosis
What is Receptor-mediated endocytosis?
A highly selective type of endocytosis by which cells take up specific ligands (ligands are molecules that bind to specific receptors)
Give a detailed explanation of how receptor-mediated endocytosis works.
- LDL particles that contain cholesterol bonds to a specific receptor in the plasma membrane to form a receptor-LDL complex. The receptors are integral membrane proteins that are concentrated in regions of the plasma membrane called the clathrin-coated pits. Here, a protein called clathrin attaches to the membrane on its cytoplasmic side. Many clathrin molecules come together, forming a basket like structure round the receptor-LDL complexes that causes the membrane to invaginate (fold inward).
- Vesicle formation - the invaginated edges of the membrane around the clathrin-coated pit fuse, and a small piece of the membrane pinches off. The resulting vesicle, known as a clathrin-coated vesicle contains the receptor-LDL complexes
- Uncoating - almost immediately the vesicle loses its clathrin coat to become an unchanged vesicle
- Fusion with endosome - the uncoated vesicle fuses with a vesicle known as an endosome. Within an endosome, the LDL particles separate from their receptors
- Recycling of receptors to plasma membrane - receptors accumulate in transport vesicles that return them to the plasma membrane
- Degradation in lysosomes - LDL particle vesicles fuse with lysosomes that contain digestive enzymes. They break down the large protein and lipid molecules of the LDL particle into amino acids, fatty acids and cholesterol. These small molecules then leave the lysosomes
What is phagocytosis?
A form of endocytosis in which the cell engulfs large solid particles, such as worn-out cells, whole bacteria or viruses
What is the name of cells that are able to carry out phagocytosis?
Phagocytes
What are the two main types of phagocytes?
Macrophages - located in many body tissues
Neutrophils - a type of white blood cell
Describe in detail the process of phagocytosis.
Begins when a particle binds to the plasma membrane receptor on the phagocyte, causing it to extend pseudopods. Pseudopods surround the particle outside of the cell and the membranes fuse to form a vesicle called a phagosome, which enters the cytoplasm. The phagosome fuses with one or more lysosomes, and the lysosomal enzymes break down the ingested material. In most cases, any undigested materials in the phagosome remain indefinitely in a vesicle called a residual body.
What are pseudopods?
Projections of its plasma membrane and cytoplasm
What is contained in a residual body?
Any undigested material in a phagosome remain indefinitely in a vesicle called a residual body. The residual body is then either secreted by the cell via exocytosis or they remain stored in the cell as lipofuscin granules.
What is bulk-phase endocytosis?
A form of endocytosis in which tiny droplets of extracellular fluid are taken up. No receptor proteins are involved. All solutes dissolved in the ECF are brought into the cell.
Describe in detail how bulk-phase endocytosis works.
The plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle pinches off from the plasma membrane and enters the cytosol. Within the cell, the vesicle fuses with a lysosome, where enzymes degrade the engulfed solutes. The resulting smaller molecules, such as amino acids and fatty acids leave the lysosome to be used elsewhere by the cell. Occurs in most cells, especially absorptive cells in the intestines and kidneys.
What is exocytosis?
Exocytosis releases materials from a cell.
Where is exocytosis especially important?
- Secretory cells that liberate digestive enzymes, hormones, mucus, and other secretions
- Nerve cells that release substances called neurotransmitters
- in some cases, waste is also released by exocytosis
How does exocytosis work?
Membrane enclosed secretory vesicles called secretory vesicles, form inside the cell, fuse with the plasma membrane and release their contents into the ECF.
What is transcytosis?
Vesicles undergo endocytosis on one side of the cell and then undergo exocytosis on the other. As the vesicles fuse with the plasma membrane, the vesicular contents are released into the extracellular fluid.
Occurs most often across the endothelial cells that line blood vessels and is a means for materials to move between blood plasma and interstitial fluid.
What is cytoplasm?
Consists of all the cellular contents between the plasma membrane and the nucleus, and has two components
- The cytosol
- Organelles (tiny structures that perform different functions in the cell)
What is cytosol?
The fluid portion of the cytoplasm that surrounds the organelles
What is the cytoskeleton?
A network of protein filaments that extends throughout the cytosol
What three types of filamentous proteins contribute to the cytoskeleton’s structure as well as structure of the organelles?
Microfilaments
Intermediate filaments
Microtubules
What are Microfilaments?
The thinnest element of the cytoskeleton
Composed of the proteins ACTIN AND MYOSIN
Most prevalent around the edge of the cell
What are the two general functions of microfilaments?
Generate movement (muscle contraction, cell division, cell locomotion) and provide mechanical support (basic shape and strength of cells) They anchor the cytoskeleton to integral proteins in the plasma membrane
What are microvilli?
Nonmotile, microscopic, fingerlike projections of the plasma membrane
Greatly increase the surface are of the cell, microvilli are abundant on cells involved in absorption (small intestine)
What are intermediate filaments?
Thicker than microfilaments but thinner than microtubules
Exceptionally strong
Usually found in parts of cells subject to mechanical stress
Help stabilize the position of organelles such as the nucleus and help attach cells to one another
What are microtubules?
The largest of the cytoskeletal components
Long, unbranched, hollow tubes composed mainly of the protein tubulin
Grow outward from the centrosome toward the periphery of the cell
Determine cell shape
Function in movement of organelles
What are organelles?
Specialized structures within the cell that have characteristic shapes, and they perform specific functions in cellular growth, maintenance, and reproduction.
Often cooperate to maintain homeostasis
What is a centrosome?
Located near the nucleus
Consists of two parts: a pair of centrioles and pericentriolar material
During cell division, centrosomes replicate so that succeeding generations of cells have the capacity for cell division
Describe the two (pair) of centrioles.
Cylindrical structures, each composed of 9 clusters of 3 microtubules (triplets) arranged in a circular pattern
The long axis of one centriole is at a right angle to the long axis of the other
What is the pericentriolar material?
Surrounding the centrioles
Contains hundreds of ring-shaped complexes composed of the protein tubulin
These tubulin are the organizing centres for growth of the mitotic spindle which plays a critical role in cell division and for microtubule formation of nondividing cells
What are two motile projections of the cell surface?
Cilia and flagella
What are cilia? (Cilium)
Numerous, hair-like projections that extend from the surface of the cell
Each cilium contains a core of 20 microtubules surrounded by plasma membrane
Each cilium is anchored to a basal body just below the surface of the plasma membrane
Causes the steady movement of fluid along the cell’s surface
What are flagella? (Flagellum)
Much longer than cilia
Usually move an entire cell (like a sperm cell)
What are ribosomes?
Are the sites for protein synthesis
Contains rRNA (ribosomal RNA)
Structurally contains two subunits (one twice the size of the other)
What do ribosomes attached to the endoplasmic reticulum do?
Synthesize proteins destined for specific organelles, for insertion in the plasma membrane, or for export from the cell
What do free ribosomes do?
Synthesize proteins used in the cytosol
Also located in mitochondria where they synthesize mitochondrial proteins
What is the endoplasmic reticulum?
The “ER” is a network of membranes in the form of flattened sacs or tubules
Extends from the nuclear envelope throughout the cytoplasm
What are the two different kinds of ER?
- Rough ER
2. Smooth ER
What is rough ER?
Is continuous with the nuclear membrane and usually is folded into a series of flattened sacs
Studded with ribosomes, the sites of protein synthesis
Produces secretory proteins, membrane proteins and many organelle proteins
What is smooth ER?
Extends from the rough ER to form a network of membrane tubules
Does not have ribosomes on the outer surface of its membrane
Contains unique enzymes that make it functionally more diverse than rough ER
Synthesizes fatty acids and steroids, helps release glucose, inactivates drugs and other potentially harmful substances
What is the Golgi complex?
Consists of 3 to 20 cisternae
Small, flattened membranous sacs with bulging edges that resemble a stack of pita bread
Often curved
What are the functions of the Golgi complex?
- Modifies, sorts, packages, and transports proteins received from the rough ER
- Forms secretory vesicles that discharge processed proteins via exocytosis into ECF ; forms membrane vesicles that ferry new molecules to the plasma membrane ; forms transport vesicles that carry molecules to other organelles
What is the entry of the Golgi complex called? What does it face?
The Cis face
Faces the rough ER
What is the exit of the Golgi complex called? What does it face?
Trans face
Faces the plasma membrane
What does the entry face of the Golgi complex do?
Receives and modifies proteins produced by the rough ER
What does the medial cisternae do?
Adds carbohydrates to proteins to form glycoproteins and lipids to proteins to form lipoproteins
What does the exit face of the Golgi complex do?
Modifies the molecules further and then sorts and packages them for transport to their destinations
What are the three general destinations for proteins that leave the Golgi complex?
Some proteins are secreted from the cell by exocytosis, some are incorporated into the plasma membrane, and some occupy storage vesicles that become lysosomes
What are lysosomes?
Membrane enclosed vesicles that form from the Golgi complex
Contain as many as 60 kinds of powerful digestive and hydrolytic enzymes that can break down a wide variety of molecules
How do lysosomes work best? Acidic or basic? How do they achieve this?
Acidic pH
Lysosomal membrane includes active transport pumps that import H+ ions
Interior pH of 5, 100 times more acidic than the pH of the cytosol
Membrane also includes transporters to move the final products of digestion into the cytosol (glucose, fatty acids, and amino acids)
What are the 4 functions of lysosomes?
- Digest substances that enter a cell via endocytosis and transport final products of digestion into cytosol
- Carry out autophagy, the digestion of worn-out organelles
- Implement autolysis, the digestion of the entire cell
- Accomplish extracellular digestion
What is autolysis?
The digestion of an entire cell
What is autophagy?
Digestion of worn-out organelles
What are peroxisomes?
Contains enzymes that can oxidize various organic substances and catalase (decompose hydrogen-peroxide)
Can self-replicate
What are proteasomes?
Tiny barrel shaped structures consisting of 4 stacked rings of proteins around a central core
Continuous destruction of unneeded, damaged, or faulty proteins
Contain enzymes that cut proteins into small peptides
What are mitochondria?
Generate most of the ATP through aerobic respiration
Referred to as “powerhouse” of the cell
Self-replicate
Mitochondria consist of what two kinds of membrane?
- Outer mitochondrial membrane
2. Inner mitochondrial membrane - contains a series of folds called mitochondrial cristae
What are the 2 functions of the mitochondria?
- Generate ATP through reactions of aerobic cellular respiration
- Play an important early role in apoptosis
What is the mitochondrial matrix?
Central fluid filled cavity if a mitochondrion
Why are the mitochondrial cristae so important?
Elaborate folds provide high surface area for the chemical reactions that are part of cellular respiration and contain some of the enzymes needed for ATP production
What is apoptosis?
Genetically programmed death of a cell
What is different about mitochondrial DNA?
It is inherited only from your mother
Can be used to trace maternal lineage
What is the nucleus?
A spherical or oval-shaped structure that usually the most prominent feature of a cell
Most cells usually only have one nucleus
What kind of cell doesn’t have a nucleus?
Mature red blood cells
What kind of cell have multiple nuclei?
Skeletal muscle cells
What separates the nucleus from the cytoplasm?
A double membrane called the nuclear envelope
How is the outer layer different from the inner layer of the nuclear envelope?
Outer layer is continuous with rough ER
What are nuclear pores?
Openings that extend through the nuclear envelope
What do nuclear pores do?
Control the movement of substances between the nucleus and the cytoplasm
Small molecules and ions move passively through by diffusion
Most large molecules cannot pass passively and must be moved actively
What are nucleoli? (Nucleolus, singular)
Inside the the nucleus, one or more spherical bodies that function in producing ribosomes
Simply a cluster of protein, DNA and RNA, not enclosed by a membrane
Sites of synthesis for rRNA, assembly of rRNA and proteins of ribosomal subunits
What are genes?
The cells hereditary units, which control cellular structure and direct cellular activities
How are genes arranged?
In chromosomes
What is a chromosome?
Each chromosome is a long molecule of DNA that is coiled together with several proteins
Human body cells have 46 chromosomes
(23 from each parent)
Has a pair of chromatids
What are the functions of the nucleus?
- Controls cellular structure
- Directs cellular activity
- Produces ribosomes in nucleoli
What is chromatin?
The complex of DNA, proteins and some RNA
Has a beads-on-a-string like structure
What is the genome?
The total genetic information carried in a cell or an organism
What is a nucleosome?
Each bead in a chromatin string
Consists of a double stranded DNA wrapped twice around a core of eight proteins called histones.
What are histones?
A core of 8 proteins found in chromatin, which help to organize the coiling and folding of DNA
What is linker DNA?
The string between the beads of nucleosomes, holds them together
What is a chromatin fiber?
In cells that are not dividing, another histone promotes coiling of nucleosomes into larger-diameter chromatin-fibre, which then folds into large loops
What is the proteome?
Refers to all of an organisms proteins.
What is gene expression?
A gene’s DNA is used as a template for synthesis of a specific protein
What are the two processes of gene expression?
- Transcription - the information encoded in a specific region of DNA is transcribed (copied) to produce a specific molecule of RNA
- Translation - the RNA attaches to a ribosome, where the information contained in the RNA is translated into a corresponding sequence of amino acids to form a new protein molecule
What is a base triplet?
A sequence of three nucleotides
What is a codon?
Each DNA base triplet is transcribed as a complementary sequence of three nucleotides called a codon
A given codon specifies a specific amino acid
What is the genetic code?
Is the set of rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids they specify
What are the three types of RNA?
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
What does mRNA do?
Directs the synthesis of a protein
What does rRNA do?
Joins with ribosomal proteins to make ribosomes
What does tRNA do?
Bonds to amino acids and holds it in place on a ribosome until it is incorporated into a protein during translation
One end carries a specific amino acid and the opposite end consists of a triplet of nucleotides called an anticodon
What is RNA polymerase?
An enzyme that catalyzes transcription of DNA
Where does transcription begin?
At the promoter, located near the beginning of the gene, where RNA polymerase attaches to the DNA
In RNA what does each base pair with?
A - U
T - A
G - C
C - G
What is a terminator?
Where transcription of DNA ends, specifies the end of a gene
What are introns?
Regions within the gene that DO NOT code for parts of proteins
What are exons?
DO code for segments of a protein
What is pre-mRNA?
Immediately after transcription, the transcript includes information from both introns and exons
What do small nuclear ribonucleoproteins do?
Remove the introns
They are enzymes that cut out the introns and splice together the exons
What happens after the small nuclear ribonucleoproteins snip off the introns?
The resulting product is a functional mRNA molecule that passes through a pore in the nuclear envelope to reach the cytoplasm, where translation takes place
What is alternative splicing?
A process in which the pre-mRNA transcribed from a gene is spliced in different ways to produce several different mRNAs
What is translation?
The nucleotide sequence in an mRNA molecule specifies the amino acid sequence of a protein
Ribosomes in the cytoplasm carry out the translation
Where is the binding site for mRNA?
On the small subunit of the ribosome
What is on the large subunit of ribosomes?
Two binding sites for tRNA
A “P” site and an “A” site
Describe how translation occurs.
- Initiator tRNA attaches to a start codon
- Large and small ribosomal subunits join to form a functional ribosome and initiator tRNA fits into position on the ribosome at the P site
- Anticodon of incoming tRNA pairs with next mRNA codon beside initiator tRNA at site A
- Amino acid on initiator tRNA forms a peptide bond with amino acid beside it
- tRNA leaves the ribosome; ribosome shifts by one codon; tRNA binds to newly exposed codon; repeat steps 3-5
- Protein synthesis stops when the ribosome reaches a stop codon on mRNA
What is always the first amino acid in a growing polypeptide?
Methionine - binds with the initiator tRNA (UAC) to mRNA (AUG)
AUG is the start codon
What roles do the P and A sites serve?
P site - holds the tRNA attached to the growing polypeptide
A site - holds the tRNA carrying the next amino acid to be added to the growing polypeptide
What is cell division?
The process by which cells reproduce themselves
What are the two types of cellular division?
Somatic cell division
Reproductive cell division
What is a somatic cell?
Any cell of the body other than a germ cell
What is a germ cell?
A gamete (sperm or oocyte) or any precursor cell destined to become a gamete
What is somatic cell division?
A cell undergoes nuclear division called mitosis and a cytoplasmic division called cytokinesis
Produces two genetically identical cells, each with the same number and kind of chromosomes as the original cell
Replaces dead or injured cells, tissue growth
What is reproductive cellular division?
The mechanism that produces gametes
Process consists of a special two step division called meiosis, in which the number of chromosomes in the nucleus is reduced by half
What is mitosis?
Produces two genetically identical cells
Part of somatic cell division
What is meiosis?
Cell division where the number of chromosomes is reduced by half
Occurs in reproductive cell division
What is the cell cycle?
Orderly sequence of events in which a somatic cell duplicates and divides in two
What are homologous chromosomes?
The two chromosomes that make up each pair are called homologous chromosomes
Contain SIMILAR genes arranged in the same (or almost the same) order
What are the sex chromosomes?
Females = two large X chromosomes Males = one X and a smaller Y chromosome
What are diploid cells?
Somatic cells contain two sets of chromosomes so they are called diploid (di=2)
What are the two major phases of cellular division?
Interphase - when a cell is NOT dividing
Mitotic - when a cell IS dividing
What are the three phases of interphase?
G1 phase
S
G2 phase
What is the G1 phase?
The interval between the mitotic phase and the S phase
The cell is metabolically active, replicates most of its organelles and cytosolic components but NOT its DNA
Replication of centrosomes begins
How long does G1 last?
8-10 hours, if the total cell time is 24 hours
What is the G0 phase?
Cells that remain in G1 for a very long time, perhaps never to divide again
Most nerve cells
What is the S phase?
The interval between G1 and G2
DNA replication occurs
How long does the S phase last for?
About 8 hours
What is the G2 phase?
Interval between S and mitotic phase
Cell growth continues
Enzymes and other proteins are synthesized in preparation for cell division
Replication of centrosomes is complete
Why must DNA replication occur before cytokinesis in somatic cell division?
So that each of the new cells will have a complete genome
How does replication of DNA occur in the S phase?
It’s helical structure partially uncoils, and the two strands separate at the points where hydrogen bonds connect base pairs
Each exposed base pairs with a new complementary base, DNA strand takes shape as chemical bonds form between neighbouring nucleotides
2 old DNA strands –> old & new DNA + old & new DNA
What are the 4 stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What happens in prophase?
Chromatin fibres condense and shorten into chromosomes
Each prophase chromosome consists of a pair of identical strands called chromatids (replicated during S phase)
Mitotic spindles form, that push the centrosomes to the poles of the cell
Nucleolus disappears and the nuclear envelope breaks down
What is a centromere?
A constricted region that holds a chromatid pair together
What happens during metaphase?
Microtubules of the mitotic spindles align the centromeres of the chromatid pairs at the exact centre of the mitotic spindle
What happens during anaphase?
Centromeres split, separating the two members of each chromatid pair, which move to opposite poles of the cell
Cytokinesis starts in late anaphase
What happens during telophase?
Begins after chromosomes stop moving
Identical sets of chromosomes, now at opposite ends of the cells, uncoil and revert to the threadlike chromatin form
Nuclear envelope forms
Mitotic spindles break up
When does cytokinesis occur?
(Division of cells organelles and cytoplasm)
Begins in late anaphase, with the formation of a cleavage furrow (a slight indentation in the plasma membrane)
It is completed after telophase
What are the three cell destinies?
- Remain alive and functioning without dividing
- Grow and divide
- Die
What are Cdk’s?
Cyclin-dependant protein kinases
Enzymes that can transfer a phosphate group from ATP to a protein to activate the protein; other enzymes can remove the phosphate group which deactivates it
Crucial in the initiation and regulation of DNA replication, mitosis and cytokinesis
What are cyclins?
Switching on and off Cdk’s
Rise and fall with cell cycle
What is necrosis?
A pathological cell death that results from tissue injury
Many adjacent cell swell, burst and spill their cytoplasm into the interstitial fluid
Debris stimulates an inflammatory response by the immune system
What is a haploid cell?
A single set of chromosomes, 23
Gametes
What are the two stages of meiosis?
Meiosis I
Meiosis II
*during the interphase before meiosis I, chromosomes of the diploid cell start to replicate - results in two genetically identical chromatids
What are the stages of Meiosis I?
Prophase I
Metaphase I
Anaphase I
Telophase I
What happens during prophase I?
Chromosomes shorten and thicken
Nuclear envelope and nucleoli disappear
Mitotic spindle forms
2 sister chromatids of each pair of homologous chromosomes pair off, (called synapis)
Parts of the chromatids of two homologous chromosomes may be exchanged
What is synasis?
Two sister chromatids of each pair of homologous chromosomes pair off
What is a tetrad?
The resulting 4 chromatids from the synopsis
What is crossing-over?
When the parts of two homologous chromosomes may be exchanged with one another
Permits an exchange of genes between chromatids of homologous chromosomes
Resulting cells are genetically UNLIKE each other
Genetically UNLIKE the starting cell that produced them
What happens in metaphase I?
The tetrads formed by homologous pairs of chromosomes line up along the metaphase plate
What happens during anaphase I?
The members of each homologous pair of chromosomes separate as they as pulled to opposite poles of the cell
What is the net effect of meiosis I?
Each resulting cell contain the haploid number of chromosomes because it contains only one member of each pair of the homologous chromosomes present in the starting cell
Summarize meiosis I and meiosis II.
Meiosis I begins with a diploid starting cell and ends with two cells, each with a haploid number of chromosomes. During meiosis II, each of the haploid cells formed in meiosis I divides, net result is 4 gametes that are genetically different from the original starting diploid cell
How does anaphase I of meiosis differ from anaphase of mitosis?
During anaphase I of meiosis, the paired chromatids are held together by a centromere and do not separate. During anaphase of mitosis, the paired chromatids separate and the centromeres spilt
What is geriatrics?
Branch of medicine that deals with the medical problems and care of elderly persons
What are telomeres?
Specific DNA sequences found only at the tips of each chromosome
Prevent them from sticking together, protect the chromosomes
With each division, the telomeres shorten
What is progeria?
Rapid aging, death normally occurs around age 13
What is cancer?
A group of diseases characterized by uncontrolled or abnormal cell division
Oncology - study of cancer
What is a malignant tumor?
Ability to spread to other parts of the body
What is a benign tumor?
Does not metastasis
What is melanomas?
Cancerous growths of skin epithelial cells that produce melanin
What is sarcoma?
Any cancer arising from muscle cells or connective tissues
What is leukaemia?
Cancer of blood-forming organs
What is lymphoma?
Malignant disease of lymphatic tissue
