CYTOLOGY THE STUDY OF CELLS - FUNCTION

CELLULAR ACTIVITIES Transport systems – Processes of Transport Across Cell Membrane The Cell Cycle – Cellular Activities from Formation to Death or Division Protein Synthesis – using DNA & RNA to make proteins

TRANSPORT SYSTEMS Passive Transport (does not require energy) Active transport (does require energy; ATP most common form)

PASSIVE TRANSPORT SYSTEMS Diffusion Facilitated diffusion Osmosis

PASSIVE TRANSPORT SYSTEMS: DIFFUSION Molecules in constant motion Molecules move from [high] to [low] Continues until Equilibrium

DIFFUSION

Diffusion through a membrane

FACILITATED TRANSPORT OR DIFFUSION Requires special proteins (enzymes) Integral Membrane Proteins “Escort” molecules across membranes (e.g. Glucose)

Facilitated Diffusion

OSMOSIS “Special case” of diffusion Only water moves Water moves across a selectively permeable membrane Water moves from [low solute] to [high solute]

OSMOSIS

Tonicity Concentration of solutes in a solution (relative to the concentration inside the cell) Isotonic = concentration is the same Hypotonic = lower concentration of solutes Hypertonic = higher concentration of solutes

TONICITY

ACTIVE TRANSPORT SYSTEMS Facilitated active transport Endocytosis Exocytosis

FACILITATED ACTIVE TRANSPORT Molecules are moved against a concentration gradient Integral Proteins act as Carrier Molecules Sodium and potassium pump moves Na + out of cell and K + into cell

Active Transport

ENDOCYTOSIS Materials accumulate at surface of plasma membrane Membrane evaginates or invaginates, pinches off Includes: - phagocytosis – engulfment of large solids (e.g. WBCs & bacteria/viruses) - pinocytosis – engulfment of extracellular fluid

EXOCYTOSIS Releases substances outside cell Secretory vesicles fuse to cell membrane Cellular products, e.g., secretion Cellular wastes

Endocytosis Exocytosis

CELL CYCLE Interphase Cell Division -Mitosis -Cytokinesis

CELL CYCLE: INTERPHASE *High metabolic activity *Protein synthesis *DNA replication (46  92)

CELL CYCLE: MITOSIS Growth & Repair 4 phases: -Prophase -Metaphase -Anaphase -Telophase

MITOSIS: PROPHASE  Chromatin condenses into chromosomes  Centrioles organize spindle  Spindle fibers attach to centromeres  Nuclear membrane disassembles  Nucleolus disassembles

MITOSIS: METAPHASE  Spindle aligns chromosomes  Alignment is around “equator”  Alignment is random

MITOSIS: ANAPHASE  “Daughter” chromosomes separate  Chromosomes are moved toward poles  Cytoplasm elongates & cytokinesis begins

MITOSIS: TELOPHASE  “Reverse” of prophase  Chromosomes relax into chromatin  Nuclear membrane reassembles  Nucleolus reassembles

CELL CYCLE: CYTOKINESIS *Division of the cytoplasm and organelles *Begins during anaphase *Completed following telophase

Mitosis

CYTOLOGY PROTEIN SYNTHESIS

Involves DNA & RNA DNA codes for proteins RNA assembles proteins Gene = a segment of DNA that codes for one protein The sequence of bases (nucleotides) carries the information

Protein Synthesis cont. T, A, C, G in DNA U, A, C, G in RNA A single gene has between 300 – 3000 base pairs In DNA, each 3-base sequence (triplet) specifies one amino acid

PROTEIN SYNTHESIS Each strand of DNA is complementary to the other Messenger RNA is complementary to DNA & carries instructions from DNA to ribosomes Protein synthesis occurs at ribosomes

RIBONUCLEIC ACID (RNA) Messenger RNA (mRNA) -polynucleotide strand that is complementary to DNA -carries instructions from DNA to ribosomes Transfer RNA (tRNA) – transports amino acids to ribosomes Ribosomal RNA (rRNA) – part of ribosomes

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DNA Replication

PHASES OF PROTEIN SYNTHESIS Transcription -Complementary mRNA is made from a DNA gene (sequence coding for a protein) Translation -mRNA’s information is used to assemble proteins with the help of tRNA & rRNA

Overview of Protein Synthesis

TRANSCRIPTION Occurs in nucleus DNA strands uncoil & separate Triplet = 3-base sequence specifying an amino acid (DNA) Codon = complementary 3-base sequence in mRNA E.g. DNA:ATA-GTA-CCC-GTA RNA:UAU-CAU-GGG-CAU

Transcription

TRANSLATION Occurs in cytoplasm mRNA enters cytoplasm & attaches to ribosome Anticodon = 3-base sequence in tRNA that is complementary to mRNA’s codon tRNA brings amino acid & binds to complementary codon on mRNA Each tRNA is specific for an amino acid

Translation

TRANSLATION continued Ribosome moves along mRNA Amino acids from adjacent tRNAs are joined by peptide bonds tRNA is released as its amino acid is added to the growing polypeptide