Ch 3 Flashcards
Cell Structure
- Plasma membrane – selectively permeable, gives form, and separates from the external environment
- ALL cells have this, separates individual units - Cytoplasm and organelles – fluid part of cell and cellular functions
- most of water stored here
- golgi bodies, lysosomes, mitochondria, etc - Nucleus – contains DNA and directs cell activities
- “brain center”
Plasma Membrane
Phospholipid barrier (double layer) between the intracellular and extracellular environments
- Hydrophobic center restricts the movement of water, water-soluble molecules, and ions
- ->hydrophobic (inside, fatty acid tails) and hydrophilic (double-layer goes to outside)
- Some substances pass through protein channels
- Proteins and phospholipids constantly move laterally – the fluid mosaic model
Membrane Proteins
• Integral proteins- span the membrane (integrated into membrane)
• Peripheral proteins- embedded on just one side of the
membrane (associated with phospholipid head)
Functions:
• Structural support
• Transport
• Enzymatic control of cell processes
• Receptors for hormones and other molecules
• Self markers for the immune system
Other Membrane Components
Carbohydrates– attached to lipids (glycolipids) and to proteins (glycoproteins); serve as antigens and interactions with regulatory molecules
Cholesterol–gives flexibility to the membrane
Phagocytosis
IN
-Bulk transport or large extracellular substances into the
cell
-Important for body defense, inflammation, and apoptosis.
Endocytosis
IN
- The plasma membrane furrows INWARD rather than extending outward.
- A small part of the membrane surrounding the substance pinches off and is brought in as a vesicle.
- May be mediated by a receptor, receptor-mediated endocytosis.
Exocytosis
OUT
Large cellular products (proteins) are moved out of the cell.
Cilia and types
tiny, hairlike structures composed of microtubules
that project from the plasma membrane
1. Primary cilium – most cells have this nonmotile cilium; may have a sensory function in some cells
2. Motile cilia- beat in unison to move substances through hollow organs. Found in respiratory tract and uterine tubes
–> motile: 9+2, nonmotile: 9+0
Flagella
a single whip-like structure that can propel a cell forward; sperm only
Microvilli
Projections off/folds in the plasma membrane that increase the surface area.
-important for absorption in intestines, reabsorb water in kidneys
Cytoplasm
Includes: organelles, a fluid called cytosol, the cytoskeleton, and inclusions (stored chemical aggregates such as glycogen).
–> may be interchangeable with “cytosol”
Cytoskeleton
“Road-map” and structural support
- system of microtubules and microfilaments in cytoplasm
- Organize the intracellular environment and allow movement of muscle cells and phagocytic cells
- Form the spindle apparatus that pulls chromosomes apart in mitosis
- facilitate vesicle and organelle movement in the cell
- -> Actin (Microfilaments - predominant), Keratin (Intermediate), Microtubules (cilia, flagella, microvilli)
Lysosomes
Organelles filled with digestive enzymes (acidic)
-Fuse with vacuoles after an immune cell engulfs a bacterium or dead cell
Primary vs. Secondary Lysosome
Primary: only contains digestive enzymes (no work yet)
Secondary: contains the partially digested contents of the food vacuole or worn-out organelles (doing work)
Autophagy
process of digesting damaged organelles and proteins in the cell (w/mistake or worn out)
Apoptosis
programmed cell death
-cell suicide - engulf WHOLE cell away from within
Necrosis
blows cell up —> releases lysosomes —> inflammatory response
-different from apoptosis
Perioxisomes
Digestive, membrane-bound organelle
- Contain enzymes specific to certain oxidative reactions; degrade long-chain fatty acids and foreign molecules
- in most cells, LOTS in liver
- generate hydrogen peroxide
- must compartmentalize b/c if blown up would kill cell w/toxic H2O2
Mitochondria
“Powerplant”
- site of energy production through aerobic cell respiration
- Most cells have mitochondria, and there can be thousands of mitochondria in a single cell
- Mitochondria can migrate and replicate; they have their own DNA, all maternal-derived
Mitochondria structure
- inner membrane, outer membrane, inter membranous space
- ->inner membrane is folded into cristae to increase surface area for reactions
- central area = fluid called “matrix”
Ribosomes
Protein factories of the cell
-Very small; made of 2 subunits of ribosomal RNA
and protein
-Found free in the cytoplasm or associated with the endoplasmic reticulum
Endoplasmic Reticulum (ER)
System of membranous passageways from the nuclear membrane to the the plasma membrane
-close to nucleus
Rough vs. Smooth ER
Rough ER: has ribosomes embedded on the outer surface, protein synthesis and modification.
Smooth ER: has NO ribosomes, synthesis of fatty acids, steroids, lipids.
Golgi Complex (Apparatus)
- Consists of stacks of hollow, flattened sacs = increased SA
- cavities are called cistern
- one side receives proteins from the ER (close to rough ER), may modify proteins
- -> proteins are packaged in vesicles called endosomes, that bud off to fuse with the plasma membrane for exocytosis
- **sending it out to wherever it needs to be” = “Distribution Center”
Cell Nucleus
- most cells have 1, muscle cells have 100s, RBCs have none
- enclosed by the nuclear envelope made of two membranes
Nucleoli: dark region not surrounded by a membrane, contains the DNA that codes for the production of ribosomal RNA
Two membranes of nucleus
Outer membrane: continuous with rough ER
Inner membrane: often fused to outer by nuclear pore complexes (which allow small molecules and RNA to move into/out of the nucleus through pores)
DNA
contained in the nucleus
- the gene on the DNA is transcribed as messenger RNA (mRNA) – GENETIC TRANSCRIPTION
- the messenger RNA is then translated at the ribosome to assemble the proper amino acid sequence – GENETIC TRANSLATION
Gene
a length of DNA that codes for a specific protein
Chromatin
—>How we package DNA - cannot be stored in long strands
-DNA in the nucleus is packaged with proteins called histones to form chromatin
-
Histones
positively charged and will interact with negatively charged DNA to cause spooling
–> creates nucleosomes (DNA + protein + histone)
Euchromatin
- ACTIVE in transcription
- looser
- chemical changes in histones (such as acetylation) allow molecules access to the DNA during gene expression
Heterochromatin
- inactive regions –> much of the DNA is inactive
- highly condensed
Transcription (RNA Synthesis)
- Start and stop regions at the beginning and end of the gene
- Promoters
- Transcription factors
- RNA Polymerase
- DNA is GCTA, RNA is CGAU
- Forms precursor messenger RNA that detaches from the DNA template
- only 1 DNA strand is transcribed
Transcription (RNA Synthesis): Promoters
areas of DNA that are not part of the gene but signal
enzymes involved where to begin transcription
Transcription (RNA Synthesis): Transcription Factors
bind to the promoter to begin transcription
Transcription (RNA Synthesis): RNA polymerase
breaks the hydrogen bonds between the base pairs of DNA and assembles the appropriate RNA nucleotide
-RNA nucleotides pair up to the DNA template
RNA Types
- Precursor messenger RNA (pre-mRNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
Precursor messenger RNA (pre-mRNA)
made directly by transcription
Messenger RNA (mRNA)
modified pre-mRNA; contains the code to make a specific protein
Transfer RNA (tRNA)
carries amino acids to mRNA for translation
–> turn nucleotide code to amino acid sequence, tRNA brings in AA
•A single strand of RNA bent into a cloverleaf shape
•One end has the anticodon, which is three nucleotides that will be complementary to the proper codon.
•The other end has the appropriate amino acid bonded by aminoacyl-tRNA synthetase enzyme
Ribosomal RNA (rRNA)
along with protein, forms ribosomes
- site of translation
- acts as an enzyme
- -> unique: ribosomal enzyme required for protein synthesis
Introns
noncoding regions within gene
-removed during mRNA synthesis/splicing
Exons
coding regions within gene
Translation (Protein Synthesis)
- mRNA attaches to a string of ribosomes to form a polyribosome
- a group of three bases on DNA (triplet), gives the complementary three base sequence in mRNA (codon)
- the codon codes for an amino acid, so the order of the codons –> the order of amino acids in a polypeptide
Post-Translational Modification
- Protein folding (chaperone proteins)
- Cross-linkage (disulfidebonds)
- Cleavage
- Addition of other molecules or groups (phosphate, methyl)
- Assembly into polymeric proteins
DNA Replication
- Before cell division, each DNA molecule must replicate.
- Involves many enzymes and proteins; two important enzymes are:
a. Helicases
b. DNA polymerase
Helicases
break hydrogen bonds between the DNA strands
- This creates a fork in the double-stranded molecule where nucleotides can be added to both strands
- -> two exact replicas of DNA strand
DNA polymerase
attaches complementary nucleotides to the exposed strand
Cell Cycle
• Divided into interphase, mitosis, and cytokinesis
• Interphase is divided into G1, S, and G2
• Mitosis is divided into Prophase, Metaphase, Anaphase, and Telophase
• Cytokinesis overlaps the last parts of mitosis
• Produces 2 identical cells to parent cell with 46 chromosomes (23 pairs)
-gives 2 identical cells w/22 pairs of chromosomes —> need to make IDENTICAL skin/gut/etc cells
Meiosis
-two cell division steps produce gametes (ova and sperm)
-only occurs in the gonads (ovaries and testes)
1st Division: Homologous chromosomes line up side by side. One member of the pair is then drawn to each pole. Each daughter cell now has 23 (not 46) chromosomes, w/two chromatids (duplicated chromosomes).
2nd Divison: chromatids are separated
- In the ovaries, three of the daughter cells die, only one becomes mature egg
- Maternal and paternal members of homologous chromosome pairs are randomly shuffled; the daughter cells from first division have randomly derived chromosomes.
- Reduction to 23 chromosomes allows for sperm and egg to combine and produce 46 chromosomes.
