This document is notes on the following chapters from Biology topics:
Chapter B1: You and your genes
• Chapter B2: Keeping healthy
• Chapter B3: Living together – food and
ecosystems
• Chapter B4: Using food and controlling
growth
• Chapter B5: The human body – staying alive
...
B1
Cells and genetic material:
➢ Cells are either prokaryotic (small, simple- bacteria cells) or eukaryotic cells (complex-
animal and human cells)
➢ Both cells contain genetic material in the form of DNA that contains instructions that
allow organisms to develop and function
Eukaryotic cells:
➢ All eukaryotic cells contain a cell membrane, cytoplasm and a nucleus
➢ Cell membrane- separates the interior of the cell from the environment outside.
Selectively permeable.
➢ Cytoplasm- located outside the nucleus, where the cell’s chemical reactions happen
➢ Nucleus- control centre of the cell, contains genetic material in the form of
chromosomes
➢ Permanent vacuole- fluid filled sac, contains membrane
➢ Ribosome- make proteins
Prokaryotic cells:
➢ Prokaryotic cells store their genetic material in a single loop of DNA and contains
plasmids
➢ Plasmids- small rings of DNA which can replicate between cells and share genetic
information
➢ Cytoplasm- where chemical reactions take place
➢ Cell wall and cell membrane- provides structure
Genome:
➢ Entire genetic material of an organism. Within a genome there are many levels of
organisation:
➢ DNA- polymer made of 2 twisted ladders to make chromosomes.
➢ Polymers- large, chain-like molecules, joined by strong covalent bonds
➢ Chromosomes- long strands of DNA coiled up to form chromosomes. Contain genes.
➢ Genes- small section of DNA. Genes code for a sequence of amino acids, which
combine to give a specific protein
➢ Nucleus of eukaryotic cell contains chromosomes made of DNA molecules, each
chromosome contains a large number of genes, each gene tells how a specific protein
should be made
➢ DNA is a polymer made of 2 long strands of units that repeat throughout the structure
called nucleotides. Each is made of a sugar, phosphate and base attached to the sugar
➢ 2 long strands within each DNA molecule are held together by attractions between
opposite bases
➢ Bases pair as such: T & A, G & C (Tigers Are Great Cats)
Nucleotides:
, ➢ DNA is a polymer made of 2 long strands that repeat throughout the structure called
nucleotides
➢ Each nucleotide is made of a sugar, phosphate and a base
DNA structure:
➢ 2 long strands within each DNA molecule are held together by attractions between
opposite bases
➢ Each base has a specific base:
➢ T and A
➢ G and C
➢ Sugar and phosphate of nucleotides form the long strands
Protein synthesis:
➢ How our bodies make proteins
➢ Codon- each amino acid is coded for by a specific sequence of 3 bases
➢ Order of bases- order of bases on DNA tell us the order for combining amino acids to
create particular proteins
➢ Different proteins- we can change the protein made by a gene by altering the
sequence of bases in that gene
➢ Process of protein synthesis reaction happens in 2 stages: transcription and translation
➢ Transcription- double stranded DNA and one strand is used to make a template of
the DNA code in the form of mRNA. The enzyme RNA polymerase joins mRNA
together. The mRNA leaves the nucleus
➢ Translation- mRNA template is used to guide protein synthesis on ribosomes located
in the cytoplasm. Specific amino acids are delivered by tRNA to add to the forming
protein chain
Alleles:
➢ Different forms of the same gene
➢ Dominant alleles- only needs one copy present to be expressed
➢ Recessive alleles- expressed if the other allele is also recessive
Genotypes and phenotypes:
➢ Genotype- combination of alleles an organism has.
➢ If 2 alleles are different the person is heterozygous
➢ If 2 alleles are same the person is homozygous
➢ Phenotype- characteristics of an individual.
➢ Determined by the interaction between the genotype and environment
Alleles:
➢ Different forms of the same gene. Can either be dominant or recessive
, ➢ Dominant alleles- always expressed regardless of the other allele. Only needs one
copy to be present. Represented by an uppercase letter
➢ Recessive alleles- only expressed if the other allele is also recessive. Represented by
lowercase letter
Genotype:
➢ Refers to the combination of alleles an organism has
➢ If the 2 alleles are different the person is called heterozygous
➢ If the 2 alleles are the same the person is called homozygous
Phenotype:
➢ An observed characteristic of an individual
➢ Determined by the interaction between genotype and environment
Gene variation:
➢ May be a result of a difference in:
➢ Genetics and environment- a combination of genetic and environmental causes
➢ Genetics- all genetic variation is the result of mutations, some of which are then
inherited and passed onto the next generation
➢ Environment- conditions in which organism develops
➢ When reproducing populations, there are many different combinations of alleles. This
means that genetic variation is high. Whilst reproduction is capable of shuffling pre-
existing alleles, only mutations can generate new alleles. Most mutations don’t affect
phenotype
Mutation:
➢ Permanent change in the nucleotide sequence of DNA
➢ Happens continuously and only affect proteins a bit if not at all. Occasionally, a mutation
may change the structure or shape of a protein. All genetic variants arise from mutations
➢ Outcome of a mutation always harms the protein function
➢ Rarely, a mutation may give survival advantage, such as resistance to an antibiotic in
bacteria
Types of mutations:
➢ The effect of a mutation depends on where on a chromosome it happened, on a section of
coded DNA or non- coded DNA
, ➢ Non- coded DNA- a mutation in non coding DNA doesn’t affect the proteins
produced by transcription and translation. It affects the transcription process by
either switching ‘on’ or ‘off’ certain genes. This causes an increase or decrease in the
amount of a protein that is produced
➢ Coding DNA- causes changes in a protein produced by DNA transcription and
translation. This can affect the protein’s structure or function
Sex determination:
➢ Healthy human body cells contain 23 pairs of chromosomes (46 chromosomes)
➢ One pair is responsible for sex determination
➢ Males have sex chromosomes XY, meaning a sperm can either contain X or Y
chromosome
➢ Females have sex chromosome XX, meaning an egg contains an X chromosome
Genome sequencing:
➢ Projects have been founded to insert new or modified genes into a cell’s genome to treat
a disease
➢ Identifying genes linked to different disorders allowing those at risk to make informed
lifestyle decisions based on the known risk factors
➢ Human genome project’s advancement leads us to the identification of genes linked to
disorders, personalization of medicine, improved understanding of inherited disorders
and advances in gene therapy
Embryonic screening:
➢ A form of genome screening where we can screen a person’s genome to look for genes
that may make that person vulnerable to genetic disorders
➢ The advantages of this are:
➢ Procedure- genome screening of a fetus is done by extracting amniotic fluid with a
needle which can help parents
➢ Suffering- could prevent suffering
➢ IVF embryos- screening would make sure implanted embryos are healthy
➢ Disadvantages of embryonic screening is:
➢ When a needle is used to extract amniotic fluid there’s a small chance it could cause
miscarriages
➢ May give false results
➢ Parents may become selective
➢ Embryos that aren’t used are destroyed- could be considered unethical or against
religions
Genetic engineering:
➢ Involves modifying an organism's genome by introducing a gene from other organisms
to produce a desired characteristic. For example:
➢ Insulin producing gene- gene that produces insulin can be inserted into bacteria,
those bacteria can then mass- produce insulin to treat people
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