OCR 21st century biology

gcse

Define a false negative test

A test that fails to detect the presence of a harmful variant when it is present (says its not there when it is)

Define a false positive test

A test that diagnoses a harmful genetic variant when it is not present (says its there when it isn't)

Define genetic screening

Similar to genetic testing, it is the study of a person's DNA in order to identify a genetic difference or susceptibility to a particular disease or abnormality.

Give two reasons why people may want to get genetic screening

People would want to know the risks of passing harmful variants to their Children. People would know if they were at risk of developing diseases later in life, and could start early treatment.

Name some different opinions concerning Genetic screening

Who else would be told about the results (individual privacy rights), Can the NHS afford the cost of genetic screening for everybody, We shouldn't interfere with nature/ God, people should know all the information that they can in order to make an informed decision, We have the tech to eliminate genetic disorders and harmful side effects - it would be wrong not to help where we can.

What is a mountant (microscopy) ?

A clear gloopy liquid used to secure the specimen in place

Why does a specimen have to be cut thinly?

Because it needs to be thin in order to allow light through it so that it is clearly visible

What is a cover slip?

A square of thin, transparent plastic or glass

How do light microscopes work?

Light microscopes work by passing light through the specimen. They let you see subcellular structures, like nuclei and chloroplasts.

Describe in steps how you would use a light microscope to view cells?

Take a thin slice of specimen

Take a slide and use a pipette to drop water on it (to secure the specimen in place.

Use tweezers to place the specimen on the slide

Add a drop of stain (so its easier to see) if the specimen is transparent/ colourless

Place a cover slip onto the slide. Press it down gently with a needle to no air bubbles are trapped.

Clip the prepared slide onto the stage of the microscope

Select the lowest powered objective lens (lowest magnification)

Use the coarse adjustment knob to move the stage so that the slide is is underneath the objective lens.

Adjust the focus with the fine adjustment knob, until you can view a clear image.

If you need to see your specimen with greater magnification, swap to a higher- powered objective lens and refocus.

Which lens should a student use first?

The lowest magnification (around X4)

Give two ways in which a student can produce accurate cell drawings based on a microscope drawing.

They should be proportional as they are in the microscope (If a section on the microscope is twice as big as another section they should convey this in their drawing).

They should not colour or shade.

Define allele

Different forms of a gene. Two copies of a gene in a pair of chromosomes are called alleles. They can be the same or different/ vary.

Describe dominant allele

Capitalised/ determines phenotype (recesive is lower case)

If R= red hair and b= brown hair, what does someone with Rb have?

Rb= Phenotype has red hair, but carries a brown hair gene.

Define hetrozygous

A dominant allele and a recessive one together (Hh/ Rr). The two alleles of a gene are different genetic variants.

Define homozygous

having two identical alleles of a gene. 2 versions of the same gene (HH/ RR). The two alleles of a gene are the same genetic variant

Define carrier

An individual who has a recessive variant but does not show the features associated with the variant because they also have a dominant variant (they are Hetrozygous). They can pass the recessive variant on to their offspring.

What are the stages of protein synthesis?

1) An mRNA template is taken from the DNA and leaves the nucleus.

2)The template is used to guide translation on Ribosomes located in the cytoplasm.

3)Specific almino acids are delivered by tRNA to the protein chain, where they are added in the order shown on the mRNA template.

4)Once completed, the long protein chain folds up, giving it its unique structure.

What does a Punnett square show?

all the possible outcomes of a genetic cross

What don't people with type 1 diabetes produce?

Insulin

What is used to replace the insulin they do not produce?

Bacteria is used because it is more effective and more ethically produced as before the insulin was taken from pigs.

How does the insulin from bacteria work in humans?

The target gene is isolated and removed from humans DNA. The target gene is removed by enzymes. In this case bacteria cells called plasmids are the vectors. They can move in and out of cells. It exits the cell and rebuilds itself with a target gene. The target gene helps produce insulin and a marker gene which is resistant to antibiotics. When antibiotics are taken only the transgenic bacteria remains. They now replicate themselves. The new bacteria replicates itself every 20 seconds which means that the diabetic person will be provided with the morally correct and effective insulin.

prokaryotic cells

Prokaryotic cells are much smaller than eukaryotic cells and have no nucleus. They store genetic material as one long circular chromosomes which floats free in the cytoplasm. Plasmids - small loops of extra DNA. They contain genes for things like drug resistance, and can be passed between prokaryotic cells. Not all prokaryotic cells contain plasmids. Unlike Eukaryotic cells they do not contain mitochondria. They are generally bacteria cells.

Eukaryotic cells

What is DNA?

deoxyribonucleic acid is a natural polymer made up of nucleotides. DNA carries the genetic code which controls how an organism develops and functions.

When was DNA discovered?

1953

Who discovered DNA?

James Watson and Francis Crick

What is a natural polymer?

A long chain molecule made up of small molecules called monomers that are joined together.

What is a nucleotide?

Nucleotides are monomers that join together to make the DNA polymer.

Describe the structure of DNA

DNA consists of two stands that are twisted together to form a double helix shape.

Where would you find your genome?

Within our cells. Every cell contains the instructions needed for our growth and development.

Explain the difference between a Eukaryotic cell and a Prokaryotic cell

Eukaryotic cells contain a nucleus. Prokaryotic cells do not

What is a gene?

A region of DNA containing the instructions for a cell that give the order of Almino acids in a protein.

What is a plasmids?

A plasmid is circular ring of bacteria

What is the difference between monomers and polymers?

The difference is that a monomer is one amino acid (e.g. Protein) and a polymer is multiple amino acids

What is mRNA?

mRNA (messenger RNA) is a substance involved in making proteins in cells. RNA stands for Ribonucletic acid. The mRNA molecule is similar to DNA but it is single stranded. It carries the DNA in the nucleus to the ribosomes in the cytoplasm.

Define and describe base pairing?

Base pairings is when 2 strands of DNA always pair up in the same way.

What does A pair with?

T

What does C pair with?

G

Describe the process of DNA molecules splitting?

When a DNA molecule is copied in order for every cell to have the same number of chromosomes. DNA splits in 1/2 with an equal number of bases on either side. Free nucleiotides pair to each free stand of DNA. Two identical strands of DNA are produced. The cell now has 92 chromosomes and can split into two cells with 46 chromosomes in each.

Define gamete?

Sex cell used in reproduction

Define homozygous

having two identical alleles of a gene

Define hetrozygous

The two alleles of a gene are different genetic variants

Define dominant allele

an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state

Define recessive allele

an allele that only has an effect on the phenotype when present in the homozygous state e.g. bb

Use these terms to explain what happens in sexual reproduction (dominant, recessive,homozygous,hetrozygous and gametes)

During sexual reproduction each offspring inherits two alleles of each gene; one allele from each gamete. The two alleles can be two copies of the same genetic variant (homozygous) or different variants (Hetrozygous) a variant can be dominant or recessive, and the combination of alleles determines what effect the gene has.

Give some pros and cons of genetic modification in plants

Pros: Higher quality, resistant, helps with food shortages and nutritious value, mass produced

Cons: Farming exploitation, dependent, destroys natural ecosystems and ethically unnatural.

Explain the process of Genetic modification in plants

Plants are genetically modified to contain vitamins and better quality. The plasmids from the bacteria is removed and cut up with the same enzymes that cut out the foreign gene. The vector (plasmid) has isolated itself and it then rebuilds itself with the foreign gene. The foreign gene provides the vitamins for the food. Genetically modified plasmid is put into the transgenic bacteria. The bacteria is inserted into plant cells. The cells are grown into the correct culture to form the planet which will produced genetically modified food.

Define genetic variants

A different version of a gene caused by mutation in the DNA this is what makes us different.

What is mRNA used for?

mRNA is used for making amino acids which makes proteins.

Define point mutation

Point mutation is when a base of the triplet code changes in mRNA.

Define insertion mutation

Insertion mutation is where a base is inserted into mRNA. This doesn't always change the protein.

Define Phenotype

physical characteristics of an organism genetic outcome.

What can genetic diagrams, and family tree and punnet squares be used for?

Genetic diagrams such as family trees and punnet squares can be used to model and predict outcomes of the inheritance of characteristics that are determined by a single gene. However, most characteristics depend on the instructions multiple genes and other parts of the genome

Describe the development of our understanding of genetics including the work of Mendel and the modern use of genome sequencing

Principles of inheritance of (single gene) characteristics were demonstrated in ideas by Gregor Mendel using pea plants. Mendle's work illustrates how scientists develop explanations that account for data they have collected. Our understanding of genetics has developed greatly since Mendel did his work; we now know that most characteristics depend on interactions between genetic variants in multiple parts of the genome. Today, scientists sequence whole genomes to investigate an organisms characteristics

Describe sex determination in humans

A human individual's sex is determined by the inheritance of genes located on sex chromosomes; specifically, genes on the Y chromosome trigger the development of tests

Where are proteins synthesisied?

In the Cytoplasm

What is the purpose of protein syntheisis?

To make proteins

DNA is found in the nucleus and cannot move out of it because it is really big. However, the cell needs to get the information from the DNA to the cell cytoplasm where proteins are syntheisised. How is this done?

By using a molecule called RNA (mRNA) which is a polymer made up of nucleotides. It is better suited for this purpose as it is shorter and just one strand

Describe in four points how proteins are made

1) The DNA contains the gene coding for the protein

2) The two DNA strands unzip in the nucleus.

3) The mRNA molecule moves out of the nucleus and into the cytoplasm where it attaches to a ribosome

4) The Amino acids are joined together in the correct order by the ribosome, following the order of the triplets in the mRNA. This makes the protein coded for by the gene.

Give examples of what structural proteins do

1) Build cells

2) Build tissue

3) More muscles

Give examples of what functional proteins do

1) Fight bacteria and viruses

2) Speed up chemical reactions in the body (enzymes which are proteins)

3)Carry oxygen around the body

4) Send chemical messages around the body

Describe a strand of DNA

DNA has 4 bases and the structure is a double helix, supporting the bases is the sugar phosphate backbone.

Explain what happens as DNA replicates

DNA replicates itself when an egg is fertilised, The DNA splits with an equal number of bases on each side. When the DNA splits the nucleotide is attached to part of the backbone and a base

Define DNA replication

The process where one DNA molecule copies itself to make two

Red blood cells have no nucleus. Why are they considered Eukaryotic?

Because red blood cells are found in animals and humans

Define Genome

The whole of the genetic information of an organism

What is needed to make a protein?

DNA and Amino acid

Define genome sequencing

A technique that works out the complete sequence of bases in an individuals genome.

Define genetic engineering

Altering the characteristics of an organism by modifying the DNA in its Genome

Define gene technology

Techniques such as genetic testing/ Engineering that our based on our understanding of the genome

Define genetic testing

Testing an individual for particular genetic variants, including those that cause diseases

Where do all genetic variants avise from

mutations

In which ways can the order of bases in DNA be changed?

If one or more nucleotides is deleted, inserted or substituted for a different nucleotide; these are mutations, and create genetic variants

Describe how genetic variants in coding DNA may influence the phenotype by altering the activity of a protein

If the sequence of bases in a gene is changed by a mutation, a protein made from it may function differently or not at all, though in some cases the mutation won't have any effect at all.