122-Biology Guide-5thPass 12/06/14. Topic 1 An overview of the topic

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1 Topic 1 Cellular Functions 1.1 The eukaryotic cell* An overview of the topic Key idea 1: Cell Organelles Key idea 2: Plasma Membrane Key idea 3: Transport Across Membrane Key idea 4: Membrane Systems GCE A level practice questions: 2011 P2 Q6a-b; 2010 P2 Q1; 2009 P2 Q1; 2007 P2 Q2; 2006 P2 Q6a & Q8; 2005 P2 Q7; 2004 P2 Q7c; 2003 P2 Q7a-b 1.2 Biological molecules* Key idea 1: Types and Features Key idea 2: Named Examples GCE A level practice questions: 2011 P2 Q6a-b; 2010 P2 Q7; 2007 P2 Q8; 2006 P2 Q8; 2005 P2 Q1a-d; 2004 P2 Q7b; 2003 P2 Q1 1.3 Enzymes* Key idea 1: Mode and Specificity of Action Key idea 2: Factors Affecting Enzyme Activity Key idea 3: Enzyme Inhibitors GCE A level practice questions: 2009 P2 Q8; 2005 P2 Q8; 2006 P2 Q2; 2004 P2 Q2; 2003 P2 Q10; 1.3 Nuclear division* Key idea 1: Mitosis Key idea 2: Significance Key idea 3: Meiosis Key idea 4: Significance GCE A level practice questions: 2009 P2 Q6; 2008 P2 Q1; 2006 P2 Q9; 2004 P2 Q2 & Q8; 2003 P2 Q2 Additional Practice Questions (detailed answers in booklet) Multiple choice questions Data analysis questions Essay questions *Note: This entire topic is relevant to the H1 syllabus except for the events of meiosis. Biology Study Guide 1

2 ЯЯ Section 1.1 The Eukaryotic Cell The cell is the basic unit of life. All living organisms are made up of cells. The plasma membrane encloses the contents of the cell. In a multicellular organism, cells are differentiated and each type of cell performs a specialised function. Bio term(s): Eukaryotic cell Prokaryotic cell Organelle The eukaryotic cell differs from a prokaryotic cell as it has a distinct and possesses membrane-bound organelles. These organelles are part of the internal structure (or ultrastructure) of the cell to help it perform its specialised function well. endoplasmic reticulum mitochondrion plasma membrance endoplasmic reticulum Golgi apparatus Golgi apparatus centriole vacuole chloroplast cell wall plasma membrane mitochondrion ƿkey ƿ idea 1 Bio term(s): Nucleus Nuclear envelope Endoplasmic reticulum Nuclear pore Cell Organelles Eukaryotic cells (i) Nucleus It is the largest organelle within the eukaryotic cell. It is enclosed with a nuclear envelope comprising of double membranes. The outer membrane is continuous with endoplasmic reticulum. Nuclear pores are present and serve as channels for molecules to move between the and cytoplasm. Nucleoplasm Mitochondria Chloroplast Within the is the semi-fluid matrix (i.e. nucleoplasm) where chromosomes are found. Most of the DNA is located in the while the rest is found in organelles such as mitochondria and chloroplasts. 2 Cellular Functions Effective Guide Biology

3 Histone Diploid cell Nucleolus Ribosomal ribonucleic acid The chromosomes are made up of DNA associated with proteins (e.g. histones). The number of chromosomes in a cell varies according to the individual species. In humans, there are 46 chromosomes in the of a somatic cell (diploid cell) while there are 23 chromosomes in the of a gamete. Within the is one or more prominent structure(s) called the nucleolus (nucleoli). Nucleoli are responsible for the synthesis of ribosomal ribonucleic acid (rrna), which is a component of ribosomes. Chromosomes Genes The contains the hereditary material (chromosomes) of an organism. The DNA contains genes which control and direct activities of a cell by regulating protein synthesis. The division of the is part of the cell division during the growth and development of the multicellular organism. smooth endoplasmic reticulum nuclear envelope mitochondrion rough lysosome ER nucleolus Nucleus Cristae intermembrane space (ii) Mitochondrion It is bound by a double membrane. The outer membrane is smooth and continuous while the inner membrane is extensively folded to form cristae. Cristae project into the semi-fluid matrix of the mitochondrion The outer and inner membranes are separated by the intermembrane space. Effective Guide Biology Cellular Functions 3

4 Mitochondrial matrix The mitochondrial matrix contains circular DNA and 70S ribosomes. The genes within the circular DNA are expressed to produce proteins. Ribosome It is the site for cellular respiration to produce ATP. Cellular respiration matrix outer membrane inner membrane intermembrane space crista stalked particles top view side view Mitochondrion Stroma Thylakoid Grana Intergranal lamellae Photosynthesis (iv) Chloroplast It is bound by double membrane. The outer membrane is smooth and continuous while the inner membrane gives rise to membranes (i.e. thylakoids) in the semi-fluid interior stroma. The stroma contains circular DNA and 70S ribsomes. The thylakoids are stacked to form grana. The grana are joined by intergranal lamellae. Photosynthetic pigments (e.g. chlorophyll) are found on grana and intergranal lamellae. It is the site for photosynthesis where sugars and other organic molecules are made. 4 Cellular Functions Effective Guide Biology

5 inner membrane intermembrane space outer membrane chloroplast DNA stroma granum ribosome thylakoid thylakoid membrane Chloroplast (iv) Endoplasmic reticulum (ER) It is bound by a single membrane. There are two types of ER the rough endoplasmic reticulum and smooth endoplasmic reticulum. Two types of ER have distinct features and functions but their membranes are connected and their internal spaces are continuous. Rough ER Cisternae Smooth ER The rough ER originates from the outer membrane of the nuclear envelope. It consists of a network of flattened membrane-bound sacs called cisternae. Ribosomes are attached on the outer surface of the membrane. The smooth ER consists of a series of interconnected tubules. Rough ER: It is the site for protein synthesis by the attached ribosomes and subsequent transport to the next cellular location (e.g. ). Polypeptides are also folded into their specific conformations. Smooth ER: It is the site of a variety of metabolic processes - lipid synthesis, metabolism of carbohydrates, detoxification of drugs and poisons and storage of calcium ions required for muscle contraction. Effective Guide Biology Cellular Functions 5

6 rough endoplasmic reticulum (RER) nuclear envelope Endoplasmic reticulum smooth endoplasmic reticulum (SER) ribosomes Golgi vesicles (v) It consists of a stack of flattened membrane-bound sacs (i.e. cisternae) and associated vesicles (i.e. Golgi vesicles). Forming/cis face Maturing/trans face Cisternae are continually being formed at one end of the Golgi body (i.e. forming face or cis face). This occurs when vesicles that bud from ER fuse with the and add their content into the lumen of the Golgi body. At the other end of the organelle (i.e. maturing face or trans face), it breaks down continually as vesicles pinch off to transport the bio-molecules elsewhere. Lysosome It is the site where proteins and other bio-molecules are sorted and packaged before transportation to their cellular destinations or secretion out of the cell. At times, the proteins are further chemically modified (e.g. attachment of carbohydrate chains to form glycoproteins). Lysosomes and cell walls are also produced by the organelle. 6 Cellular Functions Effective Guide Biology

7 cis face - receiving side of transport vesicle from rough ER cisternae new vesicles forming transport vesicle from the golgi trans face - shipping side of secretory vesicle from trans face Lipase Protease Nuclease Pathogen (vi) Lysosome They are single membrane vesicles formed from Golgi body. They contain hydrolytic enzymes (e.g. lipases, proteases, nucleases). It helps to protect the organism from pathogens or derive its food source. Materials (e.g. pathogenic bacteria or food material) taken into the cell are broken down by the hydrolytic enzymes. The products of digestion are then absorbed and assimilated by cytoplasm of cell. Autophagy Autolysis It helps to break down worn-out organelles within a cell (i.e. autophagy). When a cell is damaged beyond repair or dead, the lysosomes within release their content to initiate autolysis. Effective Guide Biology Cellular Functions 7

Basic Structure of a Cell

Basic Structure of a Cell Prokaryotic Cells No nucleus Archaea & Eubacteria One circular chromosome Extremely small Eukaryotic Cells Has a nucleus!!! Membrane-bound organelles Plants, Animals, Fungi, &