Information Storage in the Nucleus

Chapter 3

The Cellular Level of Organization

3-3 Cell Nucleus

Information Storage in the Nucleus

oDNA

Instructions for every protein in the body

oGene

DNA instructions for one protein

oGeneticcode

The chemical language of DNA instructions

oSequence of bases (A, T, C, G)

Triplet code

o3 bases = 1 amino acid

3-4 Protein Synthesis

The Role of Gene Activation in Protein Synthesis

oThe nucleus contains chromosomes

oChromosomes contain DNA

oDNA stores genetic instructions for proteins

oProteins determine cell structure and function

3-4 Protein Synthesis

The Role of Gene Activation in Protein Synthesis

oGeneactivation — uncoiling DNA to use it

Promoter

Terminator

oTranscription

Copies instructions from DNA to mRNA (in nucleus)

RNApolymerase produces messengerRNA (mRNA)

3-4 Protein Synthesis

The Role of Gene Activation in Protein Synthesis

oTranslation

Ribosome reads code from mRNA (in cytoplasm)

Assembles amino acids into polypeptide chain

oProcessing

RER and Golgi apparatus produce protein

3-4 Protein Synthesis

The Transcription of mRNA

oA gene is transcribed to mRNA in three steps

1.Geneactivation

2.DNAtomRNA

3.RNAprocessing

3-4 Protein Synthesis

Step 1: Gene activation

oUncoils DNA, removes histones

oStart (promoter) and stop codes on DNA mark location of gene

Codingstrand is code for protein

Templatestrand is used by RNA polymerase molecule

3-4 Protein Synthesis

Step 2: DNA to mRNA

oEnzyme RNA polymerase transcribes DNA

Binds to promoter (start) sequence

Reads DNA code for gene

Binds nucleotides to form messenger RNA (mRNA)

mRNA duplicates DNA coding strand, uracil replaces thymine

3-4 Protein Synthesis

Step 3: RNA processing

oAt stop signal, mRNA detaches from DNA molecule

Code is edited (RNAprocessing)

Unnecessary codes (introns) removed

Good codes (exons) spliced together

Triplet of three nucleotides (codon) represents one amino acid

3-4 Protein Synthesis

Translation

omRNA moves:

From the nucleus through a nuclear pore

omRNA moves:

To a ribosome in cytoplasm surrounded by amino acids

omRNA binds to ribosomal subunits

tRNA delivers amino acids to mRNA

3-4 Protein Synthesis

Translation

otRNAanticodon binds to mRNA codon

One mRNA codon translates to one amino acid

oEnzymes join amino acids with peptide bonds

Polypeptide chain has specific sequence of amino acids

oAt stopcodon, components separate

3-4 Protein Synthesis

How the Nucleus Controls Cell Structure and Function

1.Direct control through synthesis of:

Structural proteins

Secretions (environmental response)

2.Indirect control over metabolism through enzymes

Chapter 6

Osseous Tissue and Bone Structure

6-2 Classification of Bones

Structure of a Long Bone

oDiaphysis

The shaft

A heavy wall of compact bone, or dense bone

A central space called medullary (marrow) cavity

oEpiphysis

Wide part at each end

Articulation with other bones

Mostly spongy (cancellous) bone

Covered with compact bone (cortex)

oMetaphysis

Where diaphysis and epiphysis meet

6-2 Classification of Bones

Structure of a Flat Bone

oThe parietal bone of the skull

oResembles a sandwich of spongy bone

oBetween two layers of compact bone

oWithin the cranium, the layer of spongy bone between the compact bone is called the diploë

6-3 Bone (Osseous) Tissue

Bone (Osseous) Tissue

oDense, supportive connective tissue

oContains specialized cells

oProduces solid matrix of calcium salt deposits

oAround collagen fibers

6-3 Bone (Osseous) Tissue

Characteristics of Bone Tissue

oDense matrix, containing:

Deposits of calcium salts

Osteocytes (bone cells) within lacunae organized around blood vessels

oCanaliculi

Form pathways for blood vessels

Exchange nutrients and wastes

6-3 Bone (Osseous) Tissue

Characteristics of Bone Tissue

oPeriosteum

Covers outer surfaces of bones

Consists of outer fibrous and inner cellular layers

6-3 Bone (Osseous) Tissue

Bone Matrix

oMinerals

Two-thirds of bone matrix is calcium phosphate, Ca3(PO4)2

oReacts with calcium hydroxide, Ca(OH)2

oTo form crystals of hydroxyapatite, Ca10(PO4)6(OH)2

oWhich incorporates other calcium salts and ions

6-3 Bone (Osseous) Tissue

Bone Matrix

oMatrix proteins

One-third of bone matrix is protein fibers (collagen)

6-3 Bone (Osseous) Tissue

Bone Cells

oMake up only 2 percent of bone mass

oBone contains four types of cells

1.Osteocytes

2.Osteoblasts

3.Osteoprogenitor cells

4.Osteoclasts

6-3 Bone (Osseous) Tissue

Osteocytes

oMature bone cells that maintain the bone matrix

oLive in lacunae

oAre between layers (lamellae) of matrix

oConnect by cytoplasmic extensions through canaliculi in lamellae

oDo not divide

oTwo major functions of osteocytes

1.To maintain protein and mineral content of matrix

2.To help repair damaged bone

6-3 Bone (Osseous) Tissue

Osteoblasts

oImmature bone cells that secrete matrix compounds (osteogenesis)

oOsteoid — matrix produced by osteoblasts, but not yet calcified to form bone

oOsteoblasts surrounded by bone become osteocytes

6-3 Bone (Osseous) Tissue

Osteoprogenitor Cells

oMesenchymal stem cells that divide to produce osteoblasts

oLocated in endosteum, the inner cellular layer of periosteum

oAssist in fracture repair

6-3 Bone (Osseous) Tissue

Osteoclasts

oSecrete acids and protein-digesting enzymes

oGiant, multinucleate cells

oDissolve bone matrix and release stored minerals (osteolysis)

oDerived from stem cells that produce macrophages

6-3 Bone (Osseous) Tissue

Homeostasis

oBone building (by osteoblasts) and bone recycling (by osteoclasts) must balance

More breakdown than building, bones become weak

Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone

6-4 Compact Bone and Spongy Bone

The Structure of Compact Bone

oOsteon is the basic unit

Osteocytes are arranged in concentric lamellae

Around a central canal containing blood vessels

Perforating canals

oPerpendicular to the central canal

oCarry blood vessels into bone and marrow

6-4 Compact Bone and Spongy Bone

The Structure of Compact Bone

oCircumferential lamellae

Lamellae wrapped around the long bone

Bind osteons together

6-4 Compact Bone and Spongy Bone

The Structure of Spongy Bone

oDoes not have osteons

oThe matrix forms an open network of trabeculae

oTrabeculae have no blood vessels

oThe space between trabeculae is filled with red bone marrow

Which has blood vessels

Forms red blood cells

And supplies nutrients to osteocytes

oYellow bone marrow

In some bones, spongy bone holds yellow bone marrow

Is yellow because it stores fat

6-4 Compact Bone and Spongy Bone

Weight-Bearing Bones

oThe femur transfers weight from hip joint to knee joint

Causing tension on the lateral side of the shaft

And compression on the medial side

6-4 Compact Bone and Spongy Bone

Compact Bone Is Covered with a Membrane

oPeriosteum on the outside

Covers all bones except parts enclosed in joint capsules

Made up of an outer, fibrous layer and an inner, cellular layer

Perforating fibers:collagen fibers of the periosteum

Connect with collagen fibers in bone

And with fibers of joint capsules; attach tendons, and ligaments

6-4 Compact Bone and Spongy Bone

Functions of Periosteum

1.Isolates bone from surrounding tissues

2.Provides a route for circulatory and nervous supply

3.Participates in bone growth and repair

6-4 Compact Bone and Spongy Bone

Compact Bone Is Covered with a Membrane

oEndosteum on the inside

An incomplete cellular layer:

oLines the medullary (marrow) cavity

oCovers trabeculae of spongy bone

oLines central canals

oContains osteoblasts, osteoprogenitor cells, and osteoclasts

oIs active in bone growth and repair

6-5 Bone Formation and Growth

Bone Development

oHuman bones grow until about age 25

oOsteogenesis

Bone formation

oOssification

The process of replacing other tissues with bone

6-5 Bone Formation and Growth

Bone Development

oCalcification

The process of depositing calcium salts

Occurs during bone ossification and in other tissues

oOssification

Two main forms of ossification

1.Endochondral ossification

2.Intramembranous ossification

6-5 Bone Formation and Growth

Endochondral Ossification

oOssifies bones that originate as hyaline cartilage

oMost bones originate as hyaline cartilage

oThere are seven main steps in endochondral ossification

6-5 Bone Formation and Growth

Appositional Growth

oCompact bone thickens and strengthens long bone with layers of circumferential lamellae

6-5 Bone Formation and Growth

Epiphyseal Lines

oWhen long bone stops growing, after puberty:

Epiphyseal cartilage disappears

Is visible on x-rays as an epiphyseal line

Mature Bones

oAs long bone matures:

Osteoclasts enlarge medullary (marrow) cavity

Osteons form around blood vessels in compact bone

6-5 Bone Formation and Growth

Intramembranous Ossification

oAlso called dermal ossification

Because it occurs in the dermis

Produces dermal bones such as mandible (lower jaw) and clavicle (collarbone)

oThere are five main steps in intramembranous ossification

6-5 Bone Formation and Growth

Blood Supply of Mature Bones

1.Nutrient artery and vein

A single pair of large blood vessels

Enter the diaphysis through the nutrient foramen

Femur has more than one pair

2.Metaphyseal vessels

Supply the epiphyseal cartilage

Where bone growth occurs

3.Periosteal vessels

Blood to superficial osteons

Secondary ossification centers

6-5 Bone Formation and Growth

Lymph and Nerves

oThe periosteum also contains:

Networks of lymphatic vessels

Sensory nerves



6-6 Bone Remodeling

Process of Remodeling

oThe adult skeleton:

Maintains itself

Replaces mineral reserves

Recycles and renews bone matrix

Involves osteocytes, osteoblasts, and osteoclasts

6-6 Bone Remodeling

Process ofRemodeling

oBone continually remodels, recycles, and replaces

oTurnover rate varies:

If deposition is greater than removal, bones get stronger

If removal is faster than replacement, bones get weaker

6-7 Exercise, Hormones, and Nutrition

Effects of Exercise on Bone

oMineral recycling allows bones to adapt to stress

oHeavily stressed bones become thicker and stronger

Bone Degeneration

oBone degenerates quickly

oUp to one-third of bone mass can be lost in a few weeks of inactivity

6-7 Exercise, Hormones, and Nutrition

Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors

oA dietary source of calcium and phosphate salts

Plus small amounts of magnesium, fluoride, iron, and manganese

6-7 Exercise, Hormones, and Nutrition

Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors

oThe hormone calcitriol

Made in the kidneys

Helps absorb calcium and phosphorus from digestive tract

Synthesis requires vitamin D3 (cholecalciferol)

6-7 Exercise, Hormones, and Nutrition

Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors

oVitamin C is required for collagen synthesis and stimulation of osteoblast differentiation

oVitamin A stimulates osteoblast activity

oVitamins K and B12 help synthesize bone proteins

6-7 Exercise, Hormones, and Nutrition

Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors

oGrowth hormone and thyroxine stimulate bone growth

oEstrogens and androgens stimulate osteoblasts

oCalcitonin and parathyroid hormone regulate calcium and phosphate levels

6-8 Calcium Homeostasis

The Skeleton as a Calcium Reserve

oBones store calcium and other minerals

oCalcium is the most abundant mineral in the body

Calcium ions are vital to:

oMembranes

oNeurons

oMuscle cells, especially heart cells

6-8 Calcium Homeostasis

Calcium Regulation

oCalcium ions in body fluids

Must be closely regulated

oHomeostasis is maintained

By calcitonin and parathyroid hormone (PTH)

Which control storage, absorption, and excretion



6-8 Calcium Homeostasis

Calcitonin and Parathyroid Hormone Control

oAffect:

1.Bones

Where calcium is stored

2.Digestive tract

Where calcium is absorbed

3.Kidneys

Where calcium is excreted

6-8 Calcium Homeostasis

Parathyroid Hormone (PTH)

oProduced by parathyroid glands in neck

oIncreases calcium ion levels by:

1.Stimulating osteoclasts

2.Increasing intestinal absorption of calcium

3.Decreasing calcium excretion at kidneys

Calcitonin

oSecreted by C cells (parafollicular cells) in thyroid

oDecreases calcium ion levels by:

1.Inhibiting osteoclast activity

2.Increasing calcium excretion at kidneys

6-9 Fractures

Fractures

oCracks or breaks in bones

oCaused by physical stress

Fractures are repaired in four steps

1.Bleeding

2.Cells of the endosteum and periosteum

3.Osteoblasts

4.Osteoblasts and osteocytes remodel the fracture for up to a year

6-9 Fractures

Bleeding

oProduces a clot (fracture hematoma)

oEstablishes a fibrous network

oBone cells in the area die

Cells of the endosteum and periosteum

oDivide and migrate into fracture zone

oCalluses stabilize the break

External callus of cartilage and bone surrounds break

Internal callus develops in medullary cavity

6-9 Fractures

Osteoblasts

oReplace central cartilage of external callus

oWith spongy bone

Osteoblasts and osteocytes remodel the fracture for up to a year

oReducing bone calluses

6-9 Fractures

Major Types of Fractures

oTransverse fractures

oDisplaced fractures

oCompression fractures

oSpiral fractures

oEpiphyseal fractures

oComminuted fractures

oGreenstick fractures

oColles fractures

oPott’s fractures

6-10 Effects of Aging on the Skeletal System

Age-Related Changes

oBones become thinner and weaker with age

Osteopenia begins between ages 30 and 40

Women lose 8 percent of bone mass per decade; men lose 3 percent

oThe epiphyses, vertebrae, and jaws are most affected

Resulting in fragile limbs

Reduction in height

Tooth loss

o

6-10 Effects of Aging on the Skeletal System

Osteoporosis

oSevere bone loss

oAffects normal function

oOver age 45, occurs in:

29 percent of women

18 percent of men

6-10 Effects of Aging on the Skeletal System

Hormones and Bone Loss

oEstrogens and androgens help maintain bone mass

oBone loss in women accelerates after menopause

Cancer and Bone Loss

oCancerous tissues release osteoclast-activating factor

That stimulates osteoclasts

And produces severe osteoporosis

Chapter 10

Muscle Tissue

An Introduction to Muscle Tissue

Muscle Tissue

oA primary tissue type, divided into:

Skeletal muscle tissue

Cardiac muscle tissue

Smooth muscle tissue

10-1 Functions of Skeletal Muscle Tissue

Skeletal Muscles

oAre attached to the skeletal system

oAllow us to move

oThe muscular system

Includes only skeletal muscles

10-1 Functions of Skeletal Muscle Tissue

Six Functions of Skeletal Muscle Tissue

1.Produce skeletal movement

2.Maintain posture and body position

3.Support soft tissues

4.Guard entrances and exits

5.Maintain body temperature

6.Store nutrient reserves

10-2 Organization of Muscle

Skeletal Muscle

oMuscle tissue (muscle cells or fibers)

oConnective tissues

oNerves

oBlood vessels

10-2 Organization of Muscle

Organization of Connective Tissues

oMuscles have three layers of connective tissues

1.Epimysium

2.Perimysium

3.Endomysium

10-2 Organization of Muscle

Epimysium

oExterior collagen layer

oConnected to deep fascia

oSeparates muscle from surrounding tissues

10-2 Organization of Muscle

Perimysium

oSurrounds muscle fiber bundles (fascicles)

oContains blood vessel and nerve supply to fascicles

10-2 Organization of Muscle

Endomysium

oSurrounds individual muscle cells (muscle fibers)

oContains capillaries and nerve fibers contacting muscle cells

oContains myosatellite cells (stem cells) that repair damage

10-2 Organization of Muscle

Organization of Connective Tissues

oMuscle Attachments

Endomysium, perimysium, and epimysium come together:

oAt ends of muscles

oTo form connective tissue attachment to bone matrix

oi.e., tendon (bundle) or aponeurosis (sheet)

10-2 Organization of Muscle

Blood Vessels and Nerves

oMuscles have extensive vascular systems that:

Supply large amounts of oxygen

Supply nutrients

Carry away wastes

oSkeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

10-3 Characteristics of Skeletal Muscle Fibers

Skeletal Muscle Cells

oAre very long

oDevelop through fusion of mesodermal cells (myoblasts)

oBecome very large

oContain hundreds of nuclei

10-3 Characteristics of Skeletal Muscle Fibers

The Sarcolemma and Transverse Tubules

oThe sarcolemma

The cell membrane of a muscle fiber (cell)

Surrounds the sarcoplasm (cytoplasm of muscle fiber)

A change in transmembrane potential begins contractions

10-3 Characteristics of Skeletal Muscle Fibers

The Sarcolemma and Transverse Tubules

oTransverse tubules (T tubules)

Transmit actionpotential through cell

Allow entire muscle fiber to contract simultaneously

Have same properties as sarcolemma

10-3 Characteristics of Skeletal Muscle Fibers

Myofibrils

oLengthwise subdivisions within muscle fiber

oMade up of bundles of protein filaments (myofilaments)

oMyofilaments are responsible for muscle contraction

oTypes of myofilaments:

Thin filaments

oMade of the protein actin

Thick filaments

oMade of the protein myosin

10-3 Characteristics of Skeletal Muscle Fibers

The Sarcoplasmic Reticulum (SR)

oA membranous structure surrounding each myofibril

oHelps transmit action potential to myofibril

oSimilar in structure to smooth endoplasmic reticulum

oForms chambers (terminalcisternae) attached to T tubules

10-3 Characteristics of Skeletal Muscle Fibers

The Sarcoplasmic Reticulum (SR)

oTriad

Is formed by one Ttubule and two terminalcisternae

Cisternae

oConcentrate Ca2+ (via ion pumps)

oRelease Ca2+ into sarcomeres to begin muscle contraction

10-3 Structural Components of a Sarcomere

Sarcomeres

oThe contractile units of muscle

oStructural units of myofibrils

oForm visible patterns within myofibrils

oA striped or striated pattern within myofibrils

Alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

10-3 Structural Components of a Sarcomere

Sarcomeres

oThe A Band

M line

oThe center of the A band

oAt midline of sarcomere

The H Band

oThe area around the M line

oHas thick filaments but no thin filaments

Zone of overlap

oThe densest, darkest area on a light micrograph

oWhere thick and thin filaments overlap

10-3 Structural Components of a Sarcomere

Sarcomeres

oThe I Band

Z lines

oThe centers of the I bands

oAt two ends of sarcomere

Titin

oAre strands of protein

oReach from tips of thick filaments to the Z line

oStabilize the filaments

10-3 Structural Components of a Sarcomere

Thin Filaments

oF-actin (filamentous actin)