1. Requirements
PRACTICAL
Other
Sheets

3. Risk assessment

4. Heart or plant?
For dissection
Please complete column in data tracker

5. Exam technique support on Fridays
1pm in sc2
Sv4 forms
Head start books

6. Pages 205-207 Specification area 3.4.1
DNA and Chromosomes
Pages
Specification area

7. Specification

9. Objectives
Distinguish between the DNA in prokaryotic cells and the DNA in eukaryotic organisms
Describe the structure of a chromosome
Describe the nature of homologous chromosomes
Explain how genes are arranged on a DNA molecule
Explain what is meant by an allele

10. Possible activities Distinguish between the DNA in prokaryotic cells and the DNA in eukaryotic organisms
Use animation to show scale of chromosomes in eukaryotic cells, and how chromosomes are made of DNA and histones. Introduce the concept of a gene.
- Teacher explanation about the difference between the arrangement of DNA in prokaryotic cells and eukaryotic cells, text top p205
- Students generate a summary table comparing and contrasting prokaryotic and eukaryotic DNA

11. Prokaryote and Eukaryote DNA molecules
Prokaryotes e.g. bacteria
DNA is short
DNA is circular
DNA is not wound around proteins
Plasmid DNA maybe present
Eukaryotes e.g. plants, animals
DNA is long
DNA is linear
DNA is wound around proteins called histones and then coiled tightly to make a chromosome

12. Objective 2 Describe the structure of a chromosome
When are chromosomes visible?
Once DNA has replicated how many chromatids make up a chromosome?
Where are chromatids joined together?
What are histones?
Why is DNA packed onto histones?
What can you say about the number of chromosomes in different organisms?

13. Objective 2 Describe the structure of a chromosome
When are chromosomes visible?
Once DNA has replicated how many chromatids make up a chromosome?
Where are chromatids joined together?
What are histones?
Why is DNA packed onto histones?
What can you say about the number of chromosomes in different organisms?
During cell division
Two
Centromere
Proteins DNA wrapped around in eukaryotic cells
Because it is very long so needs to be condensed
Different organisms have different numbers of chromosomes

14. Genes in Eukaryote Cells
Eukaryotes have genetic information stored in chromosomes in the nucleus of each cell:
Nucleus contains inherited information: The total collection of genes located on chromosomes in the nucleus has the complete instructions for constructing a total organism.
Cytoplasm: The nucleus controls cell metabolism; the many chemical reactions that keep the cell alive and performing its designated role.
Nucleus
Structure of the nucleus
Nuclear pores are involved in the active transport of substances into and out of the nucleus
Nucleolus is involved in the construction of ribosomes
Nuclear membrane
encloses the nucleus in eukaryotic cells
Chromosomes are made up of DNA and protein and store the information for controlling the cell

15. Genes Outside the Nucleus in Eukaryote Cells
Ribosome
Mitochondrial
DNA
Eukaryotes have two types of organelles with their own DNA:
mitochondria
chloroplasts
The DNA of these organelles is replicated when the organelles are reproduced (independently of the DNA in the nucleus).
Mitochondrion
Chloroplast
Chloroplast DNA

16. Mitochondria and chloroplasts
Have their own DNA
Short
Circular
No histones
Just like prokaryotes
They can make their own proteins as they have ribosomes too!

17. Genes in Prokaryote Cells
Flagellum
Bacteria have no membrane- bound organelles.
Cellular reactions occur on the inner surface of the cell membrane or in the cytoplasm.
Bacterial DNA is found in:
One, large circular chromosome.
Several small chromosomal structures called plasmids.
Cytoplasm (no nucleus)
Cell membrane
Single, circular
chromosome
Ribosomes
Plasmids
Cell wall

18. Plasmid DNA Bacteria have small accessory chromosomes called plasmids.
Plasmids replicate independently of the main chromosome.
Some conjugative plasmids can be exchanged with other bacteria in a process called conjugation.
Via conjugation, plasmids can transfer antibiotic resistance to other bacteria.
Recipient bacterium
Sex pilus conducts the plasmid to the recipient bacterium
Plasmid of the conjugative type
A plasmid about to pass one strand of the DNA into the sex pilus
Plasmid of the
non-conjugative type
Donor bacterium

19. How are genes arranged on a molecule of DNA
Genes are sections of DNA. They code for a particular polypeptide
Each DNA molecule has many genes along its length
Each gene occupies a specific position on the chromosome = gene locus
A lot of the DNA in eukaryotes does not code for amino acids. It is called non coding DNA

20. Coding and non coding DNA
In eukaryotes much of the DNA in the nucleus does not code for polypeptides
Non-coding DNA exists between genes. This can be repeating sequences as if the DNA is stuttering
Exons are codes for polypeptides, introns are non-coding DNA within the gene

22. Chromosomes A
Chromosomes can be represented in different forms by using a variety of microscopes:
A: Light microscope view of a chromosome from the salivary glands of the fly Simulium.
Banding: groups of genes stained light and dark.
Puffing: areas of transcription (mRNA production).
B: Scanning electron microscope (SEM) view of sex chromosomes in the condensed state during a cell division. Individual chromatin fibers are visible.
The smaller chromosome is the ‘Y’ while the larger one is the X.
C: Transmission electron microscope (TEM) view of chromosomes lined up at the equator of a cell during the process of cell division. These chromosomes are also in the condensed state. B C

23. Chromosome States
Interphase: Chromosomes are single-armed structures during their unwound state during interphase.
Dividing cells: Chromosomes are double-armed structures, having replicated their DNA to form two chromatids in preparation for cell division.
Interphase
chromosome
This chromosome would not be visible as a coiled up structure, but unwound as a region of dense chromatin in the nucleus (as in the TEM of the nucleus above)
Replicated chromosome
prepared for cell division
Chromatin
Chromatid
Centromere

24. (double helix comprising genes)
Chromosome Structure
Histone proteins organize the DNA into tightly coiled structures (visible chromosomes) during cell division.
Coiling into compact structures allows the chromatids to separate without tangling during cell division.
Cell
Replicated chromosome
DNA molecule
(double helix comprising genes)
Individual atoms
Chromatin: a complex of DNA and protein
Histone proteins

25. Chromosome Features Chromosomes can be identified by noting:
Centromere position
Metacentric
Submetacentric or Subterminal
Acrocentric
Chromosomes can be identified by noting:
Banding patterns
Position of the centromere
Presence of satellites
Length of the chromatids
These features enable homologous pairs to be matched and therefore accurate karyotypes to be made.
Banding pattern
Chromosome length
Satellite endings

26. Human Karyotype

27. Describe the nature of homologous chromosomes
What does the prefix Homo mean?
Where does each chromosome in a homologous pair come from?
What does the word diploid mean?
What is the diploid number for humans?
Why are they called homologous?
What can be different about homologous chromosomes?
What does “Haploid mean” and what cells are involved?

28. Describe the nature of homologous chromosomes
What does the prefix Homo mean?
Where does each chromosome in a homologous pair come from?
What does the word diploid mean?
What is the diploid number for humans?
Why are they called homologous?
What can be different about homologous chromosomes?
What does “Haploid mean” and what cells are involved?
The same
Mother (maternal) and father (paternal)
Total number of chromosomes in a body cell 46
Same gene loci as each other
Different forms of the gene on each chromosome (=alleles)
HAPLOID = half the number of diploid = the number of chromosomes in a sperm/egg. Produced by meiosis

29. Explain what is meant by an allele
Give the definition of an allele
Give 2 examples of alleles of different genes
What happens to the allele if the gene mutates?

30. Objective 4 Explain what is meant by an allele
Give the definition of an allele
Give 2 examples of alleles of different genes
What happens to the allele if the gene mutates?
Different form of the same gene
Tall and dwarf in tomato plants (T t)
It mutates into a different allele.

32. Homework
Summary questions p207 MAHAC

33. Assessment
How assessed (teacher, peer, self etc.)- hide from students

34. Extension activity
A textbook stated that “The bacterial chromosome is found in the cytoplasm of the cell”. Evaluate this statement.
- Ask students to compare the structure of prokaryotic cells with mitochondria and chloroplasts, identify similarities and suggest a theory.

35. Keywords
Prokaryotic, eukaryotic, chromosomes, chromatid, centromere, homologous, diploid, gene, allele,