Cells 1 Flashcards
The Cell Theory
Cells are the smallest units of life- no living entity has been found so far without at least one cell.
• All living organisms are composed of cells- evidence to this was given with the discovery of microscopes and the observation of cork cells by R. Hook.
• Cells come from pre-existing cells by division-L. Pasteur made experiments using sterilized nutrient broth to show that no life can come without previous life. There is no spontaneous generation.
• Cells contain inherited information which controls their activities.
3 examples of Questioning the Cell Theory
- FUNGI bodies are called hyphae, contain cytoplasm and numerous nuclei, not separated by walls or membranes
- MUSCLE CELLS are very elongated, called muscle fibres, again they contain many nuclei.
- GIANT ALGAE: Acetabularia species of algae are among the largest single-celled organisms, having also a remarkably large nucleus
FUNCTIONS OF LIFE
A structure, in order to be regarded as living must show the following functions which ensure survival:
NUTRITION- through food organisms obtain energy
METABOLISM- continuous breakdown and synthesis of molecules through chemical reactions
GROWTH- increase in size
SENSITIVITY- the ability to receive environmental changes and respond accordingly HOMEOSTASIS- to keep internal environment within narrow limits
REPRODUCTION- produce offspring through an asexual or a sexual way (absence or presence of gametes)
Functions of Life and Paramecium
Paramecia are surrounded by small hairs called cilia which allow it to move (responsiveness) 4
▪ Paramecia engulf food via a specialised membranous feeding groove called a cytostome (nutrition)
▪ Food particles are enclosed within small vacuoles that contain enzymes for digestion (metabolism)
▪ Contractile vacuoles are present to expel water when necessary to keep an internal environment controlled (homeostasis)
▪ Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation (reproduction)
Functions of life and Chlorella
▪ It is photosynthetic thus produces its own food (nutrition)
▪ Reacts to stimuli such as light to move towards it (sensitivity/responsiveness) ▪ Reproduces asexually or sexually
Differentiation
- In multicellular organisms, cells are grouped together in tissues. All cells in the same tissue are similar in structure and perform the same function. However, cells may differ a lot within the same organism. Although all cells contain the same genetic material, there is a time during development that they change, a process called DIFFERENTIATION. Each cell type uses (expresses) some of the genes (switched on) while other genes are not expressed in that particular cell type (switched off), but are used in other cell types.
- Through this process we eventually have different tissues: nervous, epithelial, muscle etc.
What are Stem Cells?
Cells that retain their ability to divide and differentiate into various cell types.
AIM: To produce healthy tissue which will substitute damaged tissue or even organ.
What are the three sources of Stem Cells?
- Embryonic stem cells
Zygotes deliberately created to form early embryos (up to 64 cells). All of these cells
can give any type of tissue. - Cord blood stem cells
Blood extracted from the umbilical cord of a newborn baby. The stem cells obtained by this way can be frozen and stored for a possible use later in the baby’s life. - Adult stem cells
In an adult individual, almost all cells have been differentiated and cannot produce another cell type. Within each tissue, however, some cells remain as stem cells able to replace lost differentiated cells due to injury or disease. Unfortunately, these cells are difficult to recognize and isolate.
In some cases, treatment with stem cells can be done using tissue-specific stem cells which are easy to recognize, such as in the case of leukemia, where blood stem cells from bone marrow are used.
Treatment of Stargardt’s Disease
Stargardt’s Macular Dystrophy-inherited disease caused by a recessive allele Degeneration of photoreceptive cells in the retina of the eye and consequent blindness.
• First trial in mice with embryonic stem cells developed into retina cells-the injected cells attached to the retina of the mice and improved their vision-no rejection of the transplanted tissue.
• In 2010, it was announced in the United States’ Food and Drug Administration, to immediately initiate a clinical trial using retinal cells derived from human embryonic stem cells (hESCs) to treat patients with Stargardt’s Macular Dystrophy. A woman was the first recipient and improvement of her vision was observed.
Treatment of Leukemia
Leukemia is a type of blood cancer. Blood cells are produced and mature in the bone marrow. Special mutations in genes which control cell division may cause the onset of cancer in the blood, that is uncontrollable production of white blood cells. Adult stem cells can be used to treat leukemia:
1. Fluid, containing blood stem cells, is removed from the bone marrow of a compatible individual
2. The stem cells of this fluid are isolated and stored
3. The patient is treated with chemotherapy to kill all cancer cells.
4. The healthy stem cells are introduced into the patient’s bone marrow to start
producing new, healthy blood cells
Arguments For the use of Stem Cells:
▪ Embryonic stem cells used for therapies save lives
▪ Embryos used come from IVF processes, which are not eventually used, they are not developing-die anyway
▪ No embryo suffering-no nervous system produced at that stage
Arguments against the use of Stem Cells:
▪ Potential human being- cannot be used for experiments
▪ There will be a tendency to produce more embryos than needed
▪ Such cells have a risk for developing into tumour cells
7 functions of bacterial structures:
- Cell wall – protects the cell form bursting, keeps the shape of the cell.
- Plasma membrane – controls material exchange between the cell and the environment. Some part of it may be folded inside to produce an area for ATP synthesis by aerobic cell respiration.
- Cytoplasm – carries out all the chemical reactions of metabolism. Does not contain any membrane bound organelles.
- Ribosomes – sites of protein synthesis, smaller than eukaryotic ribosomes (70S)
- Nucleoid – contains the naked DNA. There is no membrane
- Flagellum (-a) – thin, elongated structure coming from the cell wall. They are used mainly for the movement of the cell in a corkscrew manner. They are solid, not flexible.
- Pilli – protein filaments mainly responsible for attachment with other bacteria and also used as connection bridges for DNA exchange. This process is called conjugation.
- Prokaryotic cells divide by binary fission (simple division).
Functions of animal cell organelles(1)
Plasma membrane – a partially permeable structure which controls material exchange between the cell and its environment.
• Cytoplasm – a dynamic fluid where all the organelles are found and all chemical reactions are performed.
• Nucleus(-i) - the largest organelle of the eukaryotic cell. It is surrounded by a double membrane with pores, allowing the exchange of substances between the cytoplasm and the nucleus. Inside the nucleus, uncoiled chromosomes spread in a thread-like structure called CHROMATIN. This is DNA bonded with proteins (called histones). The nucleus stores the genetic material of the cell and it is responsible for the processes of DNA replication and transcription. A darker area is found in the nucleus called the NUCLEOLUS which is responsible for rRNA synthesis and thus ribosome formation.
Functions of animal cell organelles(2)
- Rough Endoplasmic Reticulum(RER) – Flattened membrane sacs. Protein synthesis takes place here for proteins meant to be secreted out of the cell. New proteins enter the membranes of the RER and then transferred into the Golgi apparatus for secretion.
- Ribosomes – Larger than the prokaryotic (80S). They are made of two subunits the large and the small, both synthesised in the nucleolus. Their function is PROTEIN SYNTHESIS, either as part of RER or as free ribosomes in the cytoplasm. Proteins synthesized in the RER are going to be secreted out of the cell, while the ones which are synthesized on free ribosomes are going to remain inside the cell for the cell’s needs.
