Download - PART I: CELLS
PART I: CELLS
Textbook pages 65-74
PowerPoint® Lecture Slide Presentation by Patty Bostwick-Taylor, Florence-Darlington Technical College
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
PART A3
Cells and Tissues
Cells and Tissues
• Carry out all chemical activities needed to sustain life
• Cells are the building blocks of all living things• Tissues are groups of cells that are similar in
structure and function
Anatomy of the Cell
• Cells are not all the same• All cells share general structures• All cells have three main regions– Nucleus– Cytoplasm– Plasma membrane
Figure 3.1a
The Nucleus
• Control center of the cell– Contains genetic material (DNA)
• Three regions– Nuclear envelope (membrane)– Nucleolus– Chromatin
The Nucleus
Figure 3.1b
The Nucleus
• Nuclear envelope (membrane) – Barrier of the nucleus– Consists of a double membrane– Contains nuclear pores that allow for exchange of
material with the rest of the cell
The Nucleus
• Nucleoli– Nucleus contains one or more nucleoli– Sites of ribosome assembly– Ribosomes migrate into the cytoplasm through
nuclear pores
The Nucleus
• Chromatin – Composed of DNA and protein– Present when the cell is not dividing– Scattered throughout the nucleus– Condenses to form chromosomes when the cell
divides
Plasma Membrane
• Barrier for cell contents• Double phospholipid layer– Hydrophilic heads– Hydrophobic tails
• Also contains proteins, cholesterol, and glycoproteins
Plasma Membrane
Figure 3.2
Plasma Membrane Specializations
• Microvilli– Finger-like projections that increase surface area
for absorption
Plasma Membrane Specializations
• Membrane junctions– Tight junctions • Impermeable junctions • Bind cells together into leakproof sheets
– Desmosomes • Anchoring junctions that prevent cells from being
pulled apart– Gap junctions • Allow communication between cells
Plasma Membrane Specializations
Figure 3.3
Plasma Membrane Specializations
Cytoplasm
• Cytoplasm is the material outside the nucleus and inside the plasma membrane
Cytoplasm
• Contains three major elements– Cytosol• Fluid that suspends other elements
– Organelles• Metabolic machinery of the cell • “Little organs” that perform functions for the cell
– Inclusions• Chemical substances such as stored nutrients or cell
products
Cytoplasmic Organelles
Figure 3.4
Cytoplasmic Organelles
• Mitochondria– “Powerhouses” of the cell– Change shape continuously– Carry out reactions where oxygen is used to break
down food– Provides ATP for cellular energy
Cytoplasmic Organelles
• Ribosomes– Made of protein and RNA– Sites of protein synthesis– Found at two locations• Free in the cytoplasm• As part of the rough endoplasmic reticulum
Cytoplasmic Organelles
• Endoplasmic reticulum (ER)– Fluid-filled tubules for carrying substances– Two types of ER• Rough endoplasmic reticulum
– Studded with ribosomes– Synthesizes proteins
• Smooth endoplasmic reticulum– Functions in lipid metabolism and detoxification of drugs and
pesticides
Rough Endoplasmic Reticulum
Figure 3.5
Ribosome
Protein
Protein insidetransport vesicle
Transportvesicle buds off
mRNA
Rough ER
As the protein is synthesizedon the ribosome, it migratesinto the rough ER cistern.
In the cistern, the protein foldsinto its functional shape. Shortsugar chains may be attachedto the protein (forming aglycoprotein).
The protein is packaged in atiny membranous sac called atransport vesicle.
The transport vesicle buds fromthe rough ER and travels to theGolgi apparatus for furtherprocessing or goes directly tothe plasma membrane where itscontents are secreted.
Rough Endoplasmic Reticulum
Figure 3.5, step 1
Ribosome
Protein
mRNA
Rough ER
As the protein is synthesizedon the ribosome, it migratesinto the rough ER cistern.
Rough Endoplasmic Reticulum
Figure 3.5, step 2
Ribosome
Protein
mRNA
Rough ER
As the protein is synthesizedon the ribosome, it migratesinto the rough ER cistern.
In the cistern, the protein foldsinto its functional shape. Shortsugar chains may be attachedto the protein (forming aglycoprotein).
Rough Endoplasmic Reticulum
Figure 3.5, step 3
Ribosome
Protein
Transportvesicle buds off
mRNA
Rough ER
As the protein is synthesizedon the ribosome, it migratesinto the rough ER cistern.
In the cistern, the protein foldsinto its functional shape. Shortsugar chains may be attachedto the protein (forming aglycoprotein).
The protein is packaged in atiny membranous sac called atransport vesicle.
Rough Endoplasmic Reticulum
Figure 3.5, step 4
Ribosome
Protein
Protein insidetransport vesicle
Transportvesicle buds off
mRNA
Rough ER
As the protein is synthesizedon the ribosome, it migratesinto the rough ER cistern.
In the cistern, the protein foldsinto its functional shape. Shortsugar chains may be attachedto the protein (forming aglycoprotein).
The protein is packaged in atiny membranous sac called atransport vesicle.
The transport vesicle buds fromthe rough ER and travels to theGolgi apparatus for furtherprocessing or goes directly tothe plasma membrane where itscontents are secreted.
Cytoplasmic Organelles
• Golgi apparatus– Modifies and packages proteins– Produces different types of packages• Secretory vesicles• Cell membrane components• Lysosomes
Figure 3.6Extracellular fluid
Plasma membrane
Golgi vesicle containingmembrane componentsfuses with the plasmamembrane
Golgi vesicle containingdigestive enzymesbecomes a lysosome
Proteins in cisterna
Lysosome fuses withingested substancesMembrane
Transportvesicle
Pathway 3
Pathway 2
Secretory vesicles Pathway 1
Golgiapparatus
Golgi vesicle containingproteins to be secretedbecomes a secretoryvesicle
Cisterna
Rough ER
Proteins
Secretion byexocytosis
Figure 3.6, step 1Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 2Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Golgiapparatus
Cisterna
Rough ER
Pathway 1
Figure 3.6, step 3Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Golgiapparatus
Cisterna
Rough ER
Pathway 1
Figure 3.6, step 4Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Secretory vesicle Pathway 1
Golgiapparatus
Golgi vesicle containingproteins to be secretedbecomes a secretoryvesicle
Cisterna
Rough ER
Figure 3.6, step 5Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Secretory vesicles Pathway 1
Golgiapparatus
Golgi vesicle containingproteins to be secretedbecomes a secretoryvesicle
Cisterna
Rough ER
Proteins
Secretion byexocytosis
Figure 3.6, step 6Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Pathway 2Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 7Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Pathway 2Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 8Extracellular fluid
Plasma membrane
Golgi vesicle containingmembrane componentsfuses with the plasmamembrane
Proteins in cisterna
Membrane
Transportvesicle
Pathway 2Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 9Extracellular fluid
Plasma membrane
Proteins in cisterna
Membrane
Transportvesicle
Pathway 3
Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 10Extracellular fluid
Plasma membrane
Golgi vesicle containingdigestive enzymesbecomes a lysosome
Proteins in cisterna
Membrane
Transportvesicle
Pathway 3
Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 11Extracellular fluid
Plasma membrane
Golgi vesicle containingdigestive enzymesbecomes a lysosome
Proteins in cisterna
Lysosome fuses withingested substancesMembrane
Transportvesicle
Pathway 3
Golgiapparatus
Cisterna
Rough ER
Figure 3.6, step 12Extracellular fluid
Plasma membrane
Golgi vesicle containingmembrane componentsfuses with the plasmamembrane
Golgi vesicle containingdigestive enzymesbecomes a lysosome
Proteins in cisterna
Lysosome fuses withingested substancesMembrane
Transportvesicle
Pathway 3
Pathway 2
Secretory vesicles Pathway 1
Golgiapparatus
Golgi vesicle containingproteins to be secretedbecomes a secretoryvesicle
Cisterna
Rough ER
Proteins
Secretion byexocytosis
Cytoplasmic Organelles
• Lysosomes– Contain enzymes that digest worn-out or
nonusable materials within the cell
Cytoplasmic Organelles
• Peroxisomes– Membranous sacs of oxidase enzymes• Detoxify harmful substances such as alcohol and
formaldehyde• Break down free radicals (highly reactive chemicals)
– Replicate by pinching in half
Cytoplasmic Organelles
• Cytoskeleton– Network of protein structures that extend
throughout the cytoplasm– Provides the cell with an internal framework
Figure 3.7a
Figure 3.7b–d
Cytoplasmic Organelles• Cytoskeleton– Three different types of
elements• Microfilaments (largest)• Intermediate filaments• Microtubules (smallest)
Cytoplasmic Organelles
• Centrioles– Rod-shaped bodies made of microtubules– Direct the formation of mitotic spindle during cell
division
Cellular Projections
• Not found in all cells• Used for movement– Cilia move materials across the cell surface• Located in the respiratory system to move mucus
– Flagella propel the cell • The only flagellated cell in the human body is sperm
Cell Diversity
Figure 3.8a
Cell Diversity
Figure 3.8b
Cell Diversity
Figure 3.8c
Cell Diversity
Figure 3.8d
Cell Diversity
Figure 3.8e
Cell Diversity
Figure 3.8f
Cell Diversity
Figure 3.8g
Cell Physiology
Cell Physiology: Membrane Transport
• Membrane transport—movement of substances into and out of the cell
• Two basic methods of transport– Passive transport• No energy is required
– Active transport• Cell must provide metabolic energy (ATP)
Solutions and Transport
• Solution—homogeneous mixture of two or more components– Solvent—dissolving medium; typically water in the
body– Solutes—components in smaller quantities within
a solution• Intracellular fluid—nucleoplasm and cytosol• Interstitial fluid—fluid on the exterior of the
cell
Selective Permeability
• The plasma membrane allows some materials to pass while excluding others
• This permeability influences movement both into and out of the cell
Passive Transport Processes
• Diffusion– Particles tend to distribute themselves evenly within a
solution– Movement is
from high concentration to low concentration, or down a concentration gradient
Figure 3.9
Passive Transport Processes
• Types of diffusion– Simple diffusion• An unassisted process• Solutes are lipid-soluble materials or small enough to
pass through membrane pores
Passive Transport Processes
Figure 3.10a
Passive Transport Processes
• Types of diffusion (continued)– Osmosis—simple diffusion of water• Highly polar water molecules easily cross the plasma
membrane through aquaporins
Passive Transport Processes
Figure 3.10d
Passive Transport Processes
• Facilitated diffusion• Substances require a protein carrier for passive
transport• Transports lipid-insoluble and large substances
Passive Transport Processes
Figure 3.10b–c
Passive Transport Processes
• Filtration– Water and solutes are forced through a membrane
by fluid, or hydrostatic pressure– A pressure gradient must exist
• Solute-containing fluid is pushed from a high-pressure area to a lower pressure area
Active Transport Processes
• Substances are transported that are unable to pass by diffusion – Substances may be too large– Substances may not be able to dissolve in the fat
core of the membrane– Substances may have to move against a
concentration gradient• ATP is used for transport
Active Transport Processes
• Two common forms of active transport– Active transport (solute pumping)– Vesicular transport• Exocytosis • Endocytosis
– Phagocytosis– Pinocytosis
Active Transport Processes
• Active transport (solute pumping)– Amino acids, some sugars, and ions are
transported by protein carriers called solute pumps
– ATP energizes protein carriers– In most cases, substances are moved against
concentration gradients
Figure 3.11
Extracellular fluid
Cytoplasm
Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+
again; the cycle repeats.
Binding of cytoplasmic Na+
to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.
The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.
ADP
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
P
PP
ATP
Figure 3.11, step 1
Extracellular fluid
Cytoplasm
Binding of cytoplasmic Na+
to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.
ADP
Na+
Na+
Na+ P
ATP
Figure 3.11, step 2
Extracellular fluid
Cytoplasm
Binding of cytoplasmic Na+
to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.
The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.
ADP
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
P
PP
ATP
Figure 3.11, step 3
Extracellular fluid
Cytoplasm
Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+
again; the cycle repeats.
Binding of cytoplasmic Na+
to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.
The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.
ADP
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
P
PP
ATP
Active Transport Processes
• Vesicular transport– Exocytosis• Moves materials out of the cell• Material is carried in a membranous vesicle• Vesicle migrates to plasma membrane• Vesicle combines with plasma membrane• Material is emptied to the outside
Active Transport Processes: Exocytosis
Figure 3.12a
Active Transport Processes: Exocytosis
Figure 3.12b
Active Transport Processes
• Vesicular transport (continued)– Endocytosis• Extracellular substances are engulfed by being enclosed
in a membranous vescicle– Types of endocytosis• Phagocytosis—“cell eating”• Pinocytosis—“cell drinking”
Active Transport Processes: Endocytosis
Figure 3.13a
Recycling of membraneand receptors (if present)to plasma membrane
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Transport to plasmamembrane andexocytosis ofvesicle contents
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 1
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 2
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 3
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Lysosome
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 4
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 5
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Transport to plasmamembrane andexocytosis ofvesicle contents
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13a, step 6
Recycling of membraneand receptors (if present)to plasma membrane
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Transport to plasmamembrane andexocytosis ofvesicle contents
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13b–c
Active Transport Processes
Cell Life Cycle
• Cells have two major periods– Interphase• Cell grows• Cell carries on metabolic processes
– Cell division • Cell replicates itself• Function is to produce more cells for growth and repair
processes
DNA Replication
• Genetic material is duplicated and readies a cell for division into two cells
• Occurs toward the end of interphase• DNA uncoils and each side serves as a
template
DNA Replication
Figure 3.14
Events of Cell Division
• Mitosis—division of the nucleus– Results in the formation of two daughter nuclei
• Cytokinesis—division of the cytoplasm– Begins when mitosis is near completion– Results in the formation of two daughter cells
Stages of Mitosis
• Prophase– First part of cell division– Centrioles migrate to the poles to direct assembly
of mitotic spindle fibers– DNA appears as double-stranded chromosomes– Nuclear envelope breaks down and disappears
Stages of Mitosis
• Metaphase– Chromosomes are aligned in the center of the cell
on the metaphase plate
Stages of Mitosis• Anaphase– Chromosomes are pulled apart and toward the
opposite ends of the cell– Cell begins to elongate
Stages of Mitosis
• Telophase– Chromosomes uncoil to become chromatin– Nuclear envelope reforms around chromatin – Spindles break down and disappear
Stages of Mitosis
• Cytokinesis– Begins during late anaphase and completes during
telophase– A cleavage furrow forms to pinch the cells into
two parts
Stages of Mitosis
Figure 3.15
Centrioles
PlasmamembraneInterphase Early prophase Late prophase
NucleolusNuclearenvelope
Spindlepole
ChromatinCentrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Metaphase Anaphase Telophase and cytokinesisDaughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
NucleolusformingSpindleMetaphase
plate
Cleavagefurrow
Stages of Mitosis
Figure 3.15, step 1
Centrioles
Plasmamembrane
InterphaseNucleolus
Nuclearenvelope
Chromatin
Stages of Mitosis
Figure 3.15, step 2
Centrioles
Plasmamembrane
Interphase Early prophaseNucleolus
Nuclearenvelope
ChromatinCentrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Stages of Mitosis
Figure 3.15, step 3
Centrioles
Plasmamembrane
Interphase Early prophase Late prophaseNucleolus
Nuclearenvelope
Spindlepole
ChromatinCentrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Stages of Mitosis
Figure 3.15, step 4
Metaphase
Sisterchromatids
Spindle Metaphaseplate
Stages of Mitosis
Figure 3.15, step 5
Metaphase Anaphase
Daughterchromosomes
Sisterchromatids
Spindle Metaphaseplate
Stages of Mitosis
Figure 3.15, step 6
Metaphase Anaphase Telophase and cytokinesis
Daughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
Nucleolusforming
Spindle Metaphaseplate
Cleavagefurrow
Stages of Mitosis
Figure 3.15, step 7
Centrioles
PlasmamembraneInterphase Early prophase Late prophase
NucleolusNuclearenvelope
Spindlepole
ChromatinCentrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Metaphase Anaphase Telophase and cytokinesisDaughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
NucleolusformingSpindleMetaphase
plate
Cleavagefurrow
Protein Synthesis
• Gene—DNA segment that carries a blueprint for building one protein
• Proteins have many functions– Building materials for cells– Act as enzymes (biological catalysts)
• RNA is essential for protein synthesis
Role of RNA
• Transfer RNA (tRNA)– Transfers appropriate amino acids to the ribosome
for building the protein• Ribosomal RNA (rRNA)– Helps form the ribosomes where proteins are built
• Messenger RNA (mRNA)– Carries the instructions for building a protein from
the nucleus to the ribosome
Transcription and Translation
• Transcription– Transfer of information from DNA’s base sequence
to the complimentary base sequence of mRNA– Three-base sequences on mRNA are called codons
Transcription and Translation
• Translation– Base sequence of nucleic acid is translated to an
amino acid sequence– Amino acids are the building blocks of proteins
Protein Synthesis
Figure 3.16
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Synthetaseenzyme
Amino acids
Cytoplasm(site of translation)
Correct aminoacid attachedto each speciesof tRNA by anenzyme
Growing polypeptide chain
Nuclear pore
Nuclear membrane
mRNA
As the ribosomemoves along themRNA, a new aminoacid is added tothe growing proteinchain
Released tRNAreenters thecytoplasmicpool, ready tobe rechargedwith a newamino acid
Direction of ribosomeadvance; ribosome movesthe mRNA strand alongsequentially as each codonis read
Small ribosomalsubunit
Portion ofmRNA alreadytranslated
tRNA “head” bearinganticodon
Large ribosomal subunit
Peptide bond
Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via itsanticodon to thecodon
Codon
AlaPhe
Ser
GlyMet
C G G
GU UU C UCC AA G CCA U
Protein Synthesis
Figure 3.16, step 1
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
Cytoplasm(site of translation)
Nuclear pore
Nuclear membrane
mRNA
Protein Synthesis
Figure 3.16, step 2
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Cytoplasm(site of translation)
Nuclear pore
Nuclear membrane
mRNA
Small ribosomalsubunit
Large ribosomal subunit
Codon
U G CCA U
Protein Synthesis
Figure 3.16, step 3
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Synthetaseenzyme
Amino acids
Cytoplasm(site of translation)
Correct aminoacid attachedto each speciesof tRNA by anenzymeNuclear pore
Nuclear membrane
mRNA
Small ribosomalsubunit
Large ribosomal subunit
Codon
U G CCA U
Protein Synthesis
Figure 3.16, step 4
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Synthetaseenzyme
Amino acids
Cytoplasm(site of translation)
Correct aminoacid attachedto each speciesof tRNA by anenzymeNuclear pore
Nuclear membrane
mRNA
Small ribosomalsubunit
tRNA “head” bearinganticodon
Large ribosomal subunit
Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via itsanticodon to thecodon
Codon
U G CCA U
Protein Synthesis
Figure 3.16, step 5
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Synthetaseenzyme
Amino acids
Cytoplasm(site of translation)
Correct aminoacid attachedto each speciesof tRNA by anenzyme
Growing polypeptide chain
Nuclear pore
Nuclear membrane
mRNA
As the ribosomemoves along themRNA, a new aminoacid is added tothe growing proteinchain
Direction of ribosomeadvance; ribosome movesthe mRNA strand alongsequentially as each codonis read
Small ribosomalsubunit
tRNA “head” bearinganticodon
Large ribosomal subunit
Peptide bond
Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via itsanticodon to thecodon
Codon
AlaPhe
Ser
GlyMet
C G G
G C UC A G CCA U
Protein Synthesis
Figure 3.16, step 6
Nucleus(site of transcription)
DNA
mRNA specifyingone polypeptideis made onDNA template
mRNA leavesnucleus andattaches toribosome, andtranslationbegins
Synthetaseenzyme
Amino acids
Cytoplasm(site of translation)
Correct aminoacid attachedto each speciesof tRNA by anenzyme
Growing polypeptide chain
Nuclear pore
Nuclear membrane
mRNA
As the ribosomemoves along themRNA, a new aminoacid is added tothe growing proteinchain
Released tRNAreenters thecytoplasmicpool, ready tobe rechargedwith a newamino acid
Direction of ribosomeadvance; ribosome movesthe mRNA strand alongsequentially as each codonis read
Small ribosomalsubunit
Portion ofmRNA alreadytranslated
tRNA “head” bearinganticodon
Large ribosomal subunit
Peptide bond
Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via itsanticodon to thecodon
Codon
AlaPhe
Ser
GlyMet
C G G
GU UU C UCC AA G CCA U