Download Cell wk 8

Human Cell Biology and
Physiology
Timothy Billington PhD
SILVER LINING?
WHO NEEDS IT?
FIFTH FORMATIVE TEST
10th November 2016
1. A hypothetical membrane interface exists between a cell and a capillary. The following values for partial pressures (mm
mercury, Hg) of gases A and B are measured:
p p Gas A (cell) 50, (capillary), 65. p p Gas B (cell) 50, (capillary) 35.
Predict the direction of diffusion for each gas.
2. Atmospheric pressure at sea level is 760 mmHg. Percent composition of 4 gases in the atmosphere is:
Nitrogen, 78., Oxygen, 21., Carbon Dioxide, 0.03., Argon, 0.93. What partial pressure does each of the 4 gases contribute to
the total pressure?
3. Carbon Dioxide is transported in the blood stream in 3 ways. Name them and write down any possible reactions that the
gas could undergo, once in the blood stream.
4. Little Cindy is angry with her mother so she tells her mother that she will hold her breath until she turns blue and dies.
Should her mother be concerned?
5. Compare and describe External respiration and Internal respiration.
6. Name the Special Senses and the type of nerve pathway common to all.
7. Name and describe the receptor structure which operates in gustatory detection.
8. From your knowledge of vision receptors, explain why it is difficult to see colour when reading by weak moonlight.
9. What is the reason that we describe the heart as a double pump? Describe the two circuits serviced by this pump.
10. A ‘30 something’ woman goes to her GP because she is feeling unusually tired and lacks her usual energy. GP tests her
blood and tells her that she is anaemic. Explain why anaemia can lead to lack of energy and tiredness.
11. The ear senses sound waves AND motion & position of the head. Describe the cellular receptor structures operating in
both these senses.
12. Why do we use venepuncture for obtaining a blood sample, in preference to arterial puncture?
13. Relate the structure of Haemoglobin to its function in oxygen transport
Week 8 begins here
Introduction to
Cellular Metabolism
5
Physiologist’s view of Metabolism
DIET
Carbohydrates
Fats
Proteins
Lipogenesis
Free fatty acids + glycerol
Fat
stores
Glucose
Glycogenesis
Lipogenesis
Excess glucose
Glycogen
stores
Lipolysis
Urine
Excess nutrients
Metabolism in
most tissues
Body
protein
Glycogenolysis
Glucose pool
Free fatty
acid pool
Amino
acids
Protein
synthesis
Gluconeogenesis
Range of normal
plasma glucose
Amino acid
pool
Brain
metabolism
6
Metabolism is the sum of all
chemical reactions in the body
OCCUR INSIDE CELLS
7
Let’s look at some REAL
chemistry
8
Biochemist’s
view of
Metabolism
Glucose
Pyruvic
Acid
9
You see that our anaerobic
friend Glycolysis
(Glucose
Pyruvate )
is only a small part of overall
cellular metabolism
10
Q. WHAT DO WE MEAN BY ANAEROBIC?
Q. IN WHICH ORGANELLE DOES AEROBIC METABOLISM OCCUR
Metabolism by cells provides the energy needed to:
1. maintain homeostasis
2. perform essential biochemical functions
Essential functions include:
a. Metabolic turnover = periodic breakdown & replacement
of the cell’s organic components
b. Growth and cell division
c. Special processes, ( secretion, contraction and the
propagation of action potentials)
12
Amino acids, monosaccharides and fatty acids enter
the cell via the cell membrane.
Join those already in the cytoplasm
Nutrient Pool
Contains all the cell’s required organic building blocks
Cell draws on this pool to provide energy and to
create new, or repair, intracellular components
13
How does the body extract energy
from food ?
The Cell
?
?
?
14
Duality of Metabolism
Catabolic and Anabolic pathways
15
High energy level
Low
Lowenergy
energylevel
level
16
ANABOLISM = SYNTHESIS of an END PRODUCT
Synthesis always CONSUMES energy
CATABOLISM = BREAKDOWN of a COMPLEX
MOLECULE into a SIMPLER
MOLECULE
Breakdown reactions always YIELD energy
17
HOW are Anabolism and
Catabolism coupled in the cell ?
?
18
Coupling of catabolism with anabolism
19
GROWTH
Consider the elapsed time between Fertilisation and Physical Maturity
Enormous changes in complexity and organisation
Fertilisation: you have one cell
Physical maturity: ~ 70 trillion cells
TO ACCOMPLISH THIS TRANSFORMATION WE NEED CELLULAR REPRODUCTION
Cellular reproduction occurs by CELL DIVISION
We shall look at the nuclear division process called MITOSIS
Division of a single cell produces 2 daughter cells, each half the size of the parent cell
Genetic characteristics of each daughter cell are identical to those of the parent cell
DNA must be copied
Duplication of the cell’s genetic material is called DNA replication
Model of a DNA
double helix
Think of DNA
as the Molecule of
Inheritance
DNA in Human Cells
• Human cells have a cell nucleus in which DNA is
condensed & packaged
• DNA is organised into chromosomes each
representing one long DNA molecule, combined
with proteins called histones
•
23
Human chromosomes as they appear in the nucleus ( unsorted )
HUMAN CHROMOSOMES: COMPLETE SET = 46
Stained with
fluorescent dyes to
aid identification of
pairs
LET’S LOOK AT THE ULTRASTRUCTURE OF A TYPICAL CHROMOSOME
WHAT is the RELATIONSHIP b/w a CHROMOSOME and a GENE?
Let us look graphically at chromosome # 22
We will gradually subdivide it, down to just ONE gene
From Chromosome to Gene and Gene to Gene Product
This represents just 10% of the long arm of
chromosome 22
Coding
regions: 2%
28
From Chromosome to Gene and Gene to Gene Product
We now see what is in this next 10%
Coding
regions: 2%
29
From Chromosome to Gene and Gene to Gene Product
We will look at ONE of these 4 genes and its Gene Product
Gene Product = an amino acid chain
Protein = a FOLDED amino acid chain
Coding
regions: 2%
30
From Chromosome to Gene and Gene to Gene Product
Coding
regions: 2%
31
Now let’s return to the general properties of DNA
DNA strand structure
Deoxyribonucleic acid = linear
polymer of 4 different nucleotides
arranged in a specific sequence.
Each nucleotide =
one of the four nitrogenous bases,
plus a deoxyribose sugar molecule
The deoxy-ribo-nucleotides are
linked to each other by phospho-diester bonds. O-P-O
SEQUENCE of nucleotides encodes
the genetic information.
DNA Double Helix – Properties
• 2 polynucleotide chains are paired in antiparallel manner, around an imaginary common
axis.
• Nucleotide bases are internal
• Sugar phosphate backbone is on the outside
• Strands are held together by hydrogen bonds
between the nucleotide bases. Hydrogen bonds
can be likened to the horizontal rungs of a spiral
ladder.
34
DNA: base-pairing via hydrogen bonds
Nucleotide bases (C & T)
Hydrogen bonding
Nucleotide bases (A & G)
Base-pairing rules: A only pairs with T ,
C only pairs with G
35
DNA Double Helix – Properties
•Base-pairing rules (A = T and C = G) predict
• (1) the two strands complement each other
• (2) the base sequence of one strand can be
derived from that of the other
DNA Polymerase uses one strand as a
template and derives a complementary
strand
36
New strands
being synthesis
being
synthesised
DNA Helicase
DNA Polymerase
DNA REPLICATION
1. Double helix is unwound by an enzyme called DNA Helicase
2. Each of the resulting single strands is then used as a template for the synthesis
of a complementary new strand by DNA Polymerase
RESULT IS:
2 double helices
Each helix is made up of a parental strand and a newlysynthesised (daughter) strand
DNA replication
Replication is
semi-conservative
Helica
Original
double helix
Parental strands
Daughter molecules
39
CELL DIVISION – MITOSIS
Mitosis is the duplication of the 46 chromosomes in the human cell nucleus
and their subsequent separation into 2 identical sets
A single cell has divided and produced 2 daughter cells
Both daughter cells have identical DNA.
CELL DIVISION
Even when physical development is complete, cell division must continue
Essential to survival
Cells are subjected to: physical wear and tear
toxic chemicals
temperature changes/ extremes
other environmental stressors
Cells age: Life span may be hours or decades
Some cells self-destruct, controlled by the action of ‘suicide’ genes
APOPTOSIS
= Genetically-controlled cell death