Bi ol ogy Notes – To pic 7 Kat he rine Bu rk e Biology Unit 5 Joints and Movement Muscles bring about movement at a joint, at least two are needed to move a bone to and fro because muscles can only pull. A pair of muscles working in this way are described as antagonistic. A muscle that causes contraction is called an extensor while the flexor muscle contracts in the reverse movement. JOINT STRUCTURE This is an example of a synovial joint, such as those of the kip, knee and ankle. The bones that articulate in the joint are separated by a cavity filled with synovial fluid, which enables them to move freely. Muscles HOWMUSCLESWORKC h a p t e r : J o i n t s a n d M o v e m e n t 1 Other types of joints Ball-and-socket joint A round head fit into a cup-shaped socket, e.g. the hip Gliding joint Two flat surfaces slide over one another, e.g. the articulating surfaces between neighbouring vertebrae Hinge joint A convex surface fits into a concave surface, e.g. the elbowPivot joint Part of one bone fits into a ring-shaped structure and allows rotation e.g. the joint at the top of the spine The plates of the skull arefixedtogether byfibrous tissue so verylittle movement occurs, protecting the brain. In the skull of a newborn baby the joints are not yet fixed, allowing the plates to move and the skill deform (reversibly) during birth. There are spaces between the skull bones, which fill in as the plates growandfuse together. Pelvic bones are joined together bycartilage, so slight movement is possible during childbirth. This is a cartilaginous joint. There are also saddle joints in which more complex concave and convex surfaces articulate.
Muscles bring about movement at a joint, at least two are needed to move a boneto and fro because muscles can only pull. A pair of muscles working in this way
are described as antagonistic. A muscle that causes contraction is called an
extensor while the flexor muscle contracts in the reverse movement.
JOINT STRUCTURE
This is an example of a
synovial joint, such as
those of the kip, knee andankle. The bones that
articulate in the joint are
separated by a cavity
filled with synovial fluid,
which enables them to
move freely.
MusclesHOW MUSCLES WORK
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Other types of jointsBall-and-socket joint A round head fit into a cup-shaped socket, e.g. the hip
Gliding jointTwo flat surfaces slide over one another, e.g. the articulating surfaces betweenneighbouring vertebrae
Hinge joint A convex surface fits into a concave surface, e.g. the elbow
Pivot jointPart of one bone fits into a ring-shaped structure and allows rotation e.g. the joint atthe top of the spine
The plates of the skull are fixed together by fibrous tissue so very little movementoccurs, protecting the brain. In the skull of a newborn baby the joints are not yet fixed,allowing the plates to move and the skill deform (reversibly) during birth. There arespaces between the skull bones, which fill in as the plates grow and fuse together.
Pelvic bones are joined together by cartilage, so slight movement is possible duringchildbirth. This is a cartilaginous joint. There are also saddle joints in which morecomplex concave and convex surfaces articulate.
3. The banding patterns created on an extendedmuscle myofibril
Biology Notes – Topic 7 Katherine Burke
Inside each muscle fibre are numerous myofibrils which are made of a series of
contractile units called sarcomeres.
Sarcomeres are made of types of protein molecules called actin and myosin.
Actin normally makes up the thin filaments whereas myosin is mainly for
thicker filaments. Contractions are produced by co-ordinating the sliding of thefilaments in the sarcomeres. The proteins overlap and give the muscles fibres the
striated characteristic.
Where actin filaments occur on their own, there is a light band on the
sarcomeres. Where both actin filaments and myosin filaments occur, there is a
dark band. Where only myosin filaments occur, there is an intermediate
coloured band.
HOW
SARCOMERES
SHORTEN
Actin is associated with the proteins troponin and tropomyosin. The club shafts
of myosin lie together as a bundle, with heads protruding along their length. In
contraction, the change in orientation of the myosin heads brings about themovement of actin. The myosin heads attach to the actin and dip forward, sliding
actin over the myosin; this is the sliding filament theory.
THE SLIDING FILAMENT THEORY
When a nerve impulse arrives at a neuromuscular junction, calcium ions are
released from the sarcoplasmic reticulum. This is a specialised type of
endoplasmic reticulum: a system of membrane-bound sacs around the myofibrils.
The calcium ions diffuse through the sarcoplasm. This initiates the movement
of protein filaments.
1. Ca2+ attaches to the troponin molecule, causing it to move
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1. Actin and myosin filaments when the2. Actin and myosin filaments when the muscle
troponin and tropomyosin move back, once again blocking the myosin binding
sites on the actin. In the absence of ATP, the cross-bridges remain attached. This
is what happens in rigor mortis when the muscles that are contracted become
rigid.
Energy for Action The minimum energy requirement is called the basal metabolic rate (BMR),
measured in kJ g-1 h-1. It is used to measure the minimum energy requirement of
the body at rest to fuel basic metabolic processes. BMR is measured by recording
oxygen consumption under strict conditions of no food consumption for 12
hours before measurement; the body had to be totally at rest in a
thermostatically controlled room. BMR is roughly proportional to the body’s
surface area. It varies between individuals depending on their age and gender.
Percentage body fat seems to be important in accounting for these differences.
Physical activity increases the body’s total daily energy expenditure. Energy is
needed for muscle contraction to move the body but the energy can vary on how
the muscles are used. For example, an elite marathon runner uses energy at
almost half the rate of a sprinter.
Releasing energy
Food is the source of energy for all animal activity. The main energy sources are
carbohydrates and fats that have been absorbed or stored around the body.
Respiration is linked to ATP synthesis as the cells use the molecule ATP as an
energy carrier molecule.
ATP is created from ADP by the addition of Pi. In solution, phosphate ions are
hydrated and so the phosphate needs to be separated from these water
molecules to make ATP, requiring energy. ATP in water is higher in energy thanADP and phosphate ions in water, so ATP is water is a way of storing chemical
Other types of muscleMuscles found in the gut wall, blood vessels and the iris of the eye are known as smoothmuscle as their fibres do not appear to be striped. These are small cells with a single nucleus. They have a similar mechanism of contraction to skeletal muscle, using myosinand actin protein filaments. However, they are not arranged in the same way as they have gap junctions. These intercellular channels less than 2nm in diameter, and arebetween the smooth muscle cells to give cytoplasmic continuity between the cells. Thisallows chemical and electrical signals to pass between adjacent cells, and so allowssynchronised contraction. Contractions in smooth muscle fibres are slower and longer lasting and the fibres fatigue very slowly if at all.
The heart walls are made of specialised muscle fibres called cardiac muscle. These arestriped and interconnected to ensure that a co-ordinated wave of contraction occurs inthe heart. Cardiac muscle fibres do not fatigue. Neither smooth nor cardiac muscles areunder conscious control.
potential energy. ATP keeps the phosphate separated from the water, but they
can be brought together in an energy-yielding reaction every time energy is
needed for reactions within the cell.
When one phosphate group is removed from ATP by hydrolysis, ADP forms. A
small amount of energy is required to break the bond holding the end phosphatein the ATP. Once removed, the phosphate group becomes hydrated. A lot of
energy is released as bonds form between water and phosphate. This energy can
be used to supply energy-requiring reactions in the cell. Some of the energy
transferred during hydration of phosphate from ATP will raise the temperature
of the cell; some is available to drive other metabolic reactions such as muscle
contraction, protein synthesis or active transport. The hydrolysis of ATP is coupled
to these other reactions:
Carbohydrate oxidation
If exercise is low intensity, enough oxygen is supplied to cells to enable ATP to be
regenerated through aerobic respiration of fuels. Fates and carbohydrates are
oxidised to carbon dioxide and water. A summary of the equation for aerobic
respiration:
Photosynthesis was described as a process that separates hydrogen from oxygen
by photolysis. The hydrogen from water is stored by combining it was carbon
dioxide to form carbohydrate. In aerobic respiration, the hydrogen stored in
glucose is brought together with oxygen to form water again. The bonds between
hydrogen and carbon atoms in glucose are not as strong as the bonds between
hydrogen and oxygen atoms in water. Therefore, the input of energy needed to
break the bonds in glucose and oxygen is not as great as the energy released
when the bonds in carbon dioxide and water are formed. Overall, there is a
release of energy and this can be used to generate ATP.
Glucose and oxygen are not brought together directly, as this would release large
amounts of energy too quickly and therefore damage the cell. Glucose is split
apart in a series of small steps with carbon dioxide as the waste product.Hydrogen from the glucose is eventually reunited with oxygen to release large
The hydrogen ions diffuse down this electrochemical gradient through hollow
protein channels in stalked particles on the membrane. As the hydrogen ions pass
through the channel, ATP synthesis is catalysed by ATPase located in each
stalked particle. The hydrogen ions cause a conformational change in the
enzyme’s active site, so the ADP can bind.
Within the matrix, the hydrogen ions and electrons recombine to form hydrogen
atoms. These combine with oxygen to form water. The oxygen, acting as the final
carrier in the electron transport chain, is thus reduced. This method of ATP
synthesis is known as oxidative phosphorylation.
HOW MUCH ATP IS PRODUCED?
The total number of ATP produced by one glucose molecule can vary according to
the efficiency of the cell. A simple explanation would give a maximum number of
38 ATP molecules per glucose molecule. This is based on the assumption that
that reduced NAD that is reoxidised results in the formation of three ATPmolecules and each reduced FAD results in production of two ATP molecules.
RATE OF RESPIRATION
The rate of aerobic respiration can conveniently be determined by measuring the
uptake of oxygen using a respirometer. The rate is determined by the any factor
affecting the rate of the enzyme-controlled reactions.
The concentration of ATP in the cell has a role in the control of respiration. ATPinhibits the enzyme in the first step of glycolysis, the phosphorylation of glucose.
The enzyme responsible for glucose phosphorylation can exist in two different
forms. As the ATP is broken down, the enzyme is converted back to the active form
and catalysis the phosphorylation of glucose. This is known as end point inhibition.
