Biology - Chapter 3: Cell structure

Describe the structure and function of the nucleus

-Structures

• Nuclear envelope and pores

• Chromosomes in the nucleoplasm

• Nucleolus

-Functions

• DNA replication

• Stores genetic code for polypeptides

• Production of mRNA (transcription)

• (Nucleolus makes) ribosomes

Name the substances that ribosomes are made of. (1)

• Ribosomal RNA (rRNA) and protein

Describe the function of ribosomes. (1)

• Protein synthesis by translation

Name the polymers that make plant and fungal cell wall. (2)

• Plant = cellulose

• Fungus = chitin

Describe the functions of golgi apparatus. (2)

• Modify/transport proteins

• Modify/transport lipids

• Produce vesicles

Describe the role of organelles in production and release of enzyme. (5)

• DNA in nucleus codes for enzyme

• Ribosomes/rough endoplasmic reticulum produce protein by translation

• Rough endoplasmic reticulum transports/modifies protein

• Mitochondria produce ATP

• Golgi apparatus modify/transport enzyme or produce vesicles

• Vesicles move enzyme to cell membrane for exocytosis

Describe how DNA is stored in a eukaryotic cell. (2)

• DNA stored in a nucleus

• DNA associated with histone proteins forming chromatin

• DNA in mitochondria and chloroplasts

Compare the structure of chloroplasts and mitochondria. (6)

-Similarities

• Double membrane

• Circular DNA

• 70s ribosomes

-Differences

• Thylakoids in chloroplasts but cristae in mitochondria

• Stroma in chloroplasts but matrix in mitochondria

• Only chloroplasts have chlorophyll

• Only chloroplasts have starch grains

Describe the role of a mitochondrion. (1)

• Produce ATP (not energy) by aerobic respiration

Compare the organelles in all eukaryotic cells and all prokaryotic cells. (6)

-Similarities

• Cytoplasm

• Cell membrane

- Differences

• Only eukaryotic cells have membrane-bound organelles e.g. nucleus, endoplasmic reticulum

• Eukaryotic cells have genetic material stored in a nucleus whereas prokaryotic cells have circular DNA

• Eukaryotic cells have 80s ribosomes whereas prokaryotic cells have 70s ribosomes

• Only prokaryotic cells have a murein cell wall

Describe DNA in a prokaryotic cell. (2)

• Circular DNA

• No introns or histone proteins

• Some prokaryotic cells have plasmids

Describe differences between prokaryotic and eukaryotic DNA. (5)

In prokaryotic cells:

• No histones

• Circular, not linear

• Plasmids

• No introns

• Shorter DNA

Describe binary fission in bacteria. (3)

• Replication of DNA

• Replication of plasmids

• Division of cytoplasm

Describe the structures in a virus. (3)

• Nucleic acid genome inside capsid

• With reverse transcriptase if RNA

• Capsid surrounded by lipid envelope

• Attachment proteins on lipid envelope

Describe how viruses are replicated. (5)

• Viral attachment protein binds to receptors

• Nucleic acid enters cell

• Reverse transcriptase produces DNA from RNA

• Nucleic acid replicates inside cell

• Viral proteins produced (transcription and translation)

• Virus particle assembled and released from cell

Describe how you would use cell fractionation and ultracentrifugation to produce a sample of ribosomes from muscle tissue. (4)

• Homogenise tissue then filter

• Use cold, buffered, isotonic solution

• Centrifuge at low speed and remove nuclei pellet

• Centrifuge at faster speeds and remove mitochondria, membrane and then ribosome pellets

Describe and explain how you would use cell fractionation and ultracentrifugation to produce a sample of nuclei from tissue. (5)

• Homogenise to break open cells

• Filter to remove large cellular debris

• Cold solution to prevent enzyme activity

• Isotonic solution to prevent organelle lysis

• Buffered solution to prevent proteins denaturing

• Spin at low speed to move nuclei to the bottom of the tube

Describe how large organelles are removed from a suspension of cell contents. (2)

• Centrifuge at increasing speeds

• Most dense organelles in pellet and less dense organelles in supernatant

Define magnification. (1)

• Magnification = Image size ÷ actual size

Describe evidence that a microscope image was taken with an electron microscope. (3)

- Transmission electron microscope:

• Small objects (mitochondria, ribosomes) visible

• Details (membrane bilayer, cristae) visible

• Very high resolution

- Scanning electron microscope

• 3D image

Explain why an electron microscope produces better images than a light microscope. (2)

• Higher resolution

• Electrons have a shorter wavelength than light

Describe how a transmission electron microscope is different from a light microscope. (5)

• Uses electrons and not light o Greater resolution

• Smaller organelles/structures can be seen

• Cannot view live specimens

• Does not show colour (light can)

• Thinner specimens

• More complex preparation

• Uses magnets (instead of lenses)

1. Describe the appearance and behaviour of chromosomes during prophase, metaphase, anaphase and telophase of mitosis. (2 marks /stage)

-Prophase:

• Chromosomes condense

• Chromosomes become visible

• Chromosomes arranged randomly

• Because not fully attached to spindles

-Metaphase:

• Chromosomes attached to spindle fibres by centromere

• Chromosomes line up on equator of cell

-Anaphase:

• Centromeres divide

• Chromatids move to opposite poles of cell

-Telophase:

• Chromosomes contained in two nuclei

• Chromosomes condensed

Give the equation to calculate mitotic index. (1)

• Mitotic index, MI = number of cells in mitosis ÷ total number of cells in field of view

Describe how the chromosomes change during the cell cycle. (5)

• Chromosomes uncondensed during interphase

• Chromosomes replicated during S phase so made of 2 chromatids joined at centromere

• Chromosomes condense during mitosis (prophase)

• Centromere splits during anaphase so each chromosome is one chromatid

• Chromosomes uncondensed during telophase

Describe how number of chromosomes and mass of DNA per cell changes during DNA replication and cytokinesis. (4)

-DNA replication

• Mass of DNA doubles

• Number of chromosomes stays the same

-Cytokinesis

• Mass of DNA halves

• Number of chromosomes halves

Describe cytokinesis. (1)

• Splitting of cytoplasm or pinching of cell membrane

Define cancer. (1)

• Uncontrolled cell division

Describe a tumour. (2)

• Mass of cells

• (Caused by) Uncontrolled cell division

Describe and explain how to prepare a root squash slide to observe mitosis. (4)

• Cut the last 5mm of the root as that is where mitosis occurs

• Place the cells in acid to break down the links between cells

• Add stain to make the chromosomes visible

• Press down the coverslip to create a thin layer of cells so light can pass through