Inheritance + Evolution

DNA Full Form

Deoxyribonucleic acid

DNA

• Chemical that all the material in a cell is made up from

• Determines Inherited Characteristics

Chromosomes

- Located in the nucleus
46 in each cell

- 23 Chromosome Pairs (one from father and mother)

- Coiled up DNA

What are chromosones?

A chromosome is a long DNA molecule with part of the genetic material of an organism

Structure of DNA

• Tightly coiled and contained in chromosomes

• DNA is a polymer (larger molecule built from smaller molecules)

• Made up of two strands wrapped around each other to form a double helix

Sex Chromosomes

• 23rd pair of chromosomes

• Determine whether individual is male or female

What Sex Chromosomes determine gender?

• Female (XX)

• Male (XY)

Gene

• A gene is a small section of DNA found on a chromosome

• Each gene codes for a particular sequence of amino acids

• To make a specific protein

• Controls our characteristics as they code for proteins that play an important role in what our cells do

DNA with Cells

• Can determine the type of protein the cell produces

• which can determine what type of cell it is.

• Haemoglobin - Red blood cell

Number of amino acids?

• only 20 AA

• But there are multiple combinations that make thousand of different proteins

• Genes simply tell what order to put the AA together

Genome

• A genome is the entire set of genetic material in an organism

Human Genome Project Benefits

- Helps to understand and give effective treatments to inherited diseases/disorders

- Helps to search for genes linked to different types of diseases

- Use in tracing human migration patterns from the past

Nucleotide

• The monomers of DNA consisting of a common sugar,

• a phosphate group

• and one of four chemical bases (A, T, C, G) attached to the sugar.

DNA in terms of polymers/monomers

• DNA is a polymer

• Made from four different nucleotides

• Made from repeating nucleotide units

Nucleotide Structure

- Deoxyribose Sugar

- Nitrogenous Base

- Sugar and Phosphate form a backbone which is the strand

- Sugar and Phosphate groups Alternate

- The bases join together with hydrogen bonds if complementary

What are long strands of DNA made up of?

• Consists of alternating sugar and phosphate sections

Four Types of Bases

• Adenine (A),

• Cytosine (C),

• Thymine (T)

• Guanine (G)

Complementary Base Pairing

• The bases on each strand pair up with each other, holding the two strands of DNA in the double helix

• The bases always pair up in the same way:

  • Adenine always pairs with Thymine (A-T)

  • Cytosine always pairs with Guanine (C-G)

How many bases code for a particular amino acid?

• 3 Bases

• Codon/Triplet

• Order of bases control the order in which amino acids are assembled to produce a particular protein

3 Uses of Protein

Enzymes - biological catalysts that speed up chemical reactions in the body

Hormones - used to carry messages around the body

Structural Proteins - provide structure and are physically strong

Non Coding DNA

• DNA which does not code for a protein

• Switches parts of genes on and off

• controls gene expression.

Gene

A SMALL section of DNA that codes for a specific sequence of amino acids that join together to form different types of proteins.

(in exam say codes for a specific protein)

Transcription

• Process of copying a single gene of DNA to mRNA

• Takes place in the nucleus

mRNA vs DNA

• mRNA is shorter than DNA

• mRNA is single-stranded whereas DNA is double stranded

• mRNA contains uracil (U) instead of DNA Thymine (T)

Where does mRNA go after transcription?

• To ribosomes

Translation

• Process by which a ribosome combines amino acids together to form a protein using instructions of mRNA

Ribosome function

• To carry out protein synthesis

• By assembling amino acids that fold up to form proteins

Polypeptide

• Chain of amino acids

Transcription Steps (Protein Synthesis)

- RNA polymerase makes a complementary mRNA base in small parts at a time of the gene

- Gene closes and opens right after the RNA creates the base for it

-messenger RNA takes it to the ribosome

Translation Steps (Protein Synthesis)

- The ribosome 'reads' the code on the mRNA in groups of three

- Each triplet of bases codes for a specific amino acid

- tRNA bring specific amino acids to add to the growing protein chain in the correct order (due to its anti-codon being complementary)

- In this way, the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein

- Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein

Coding for Amino Acids

• Sequence of three bases (triplet/codon) code for a particular amino acid

• Order of bases controls the order and different types of amino acids that are joined together’

• AA sequence → particular type of protein

• Order of bases in DNA eventually determine which proteins are produced

Double Helix Structure

• phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand

• base pairs connect to form the middle (complementary hydrogen bonds)

• Sequence of bases holds code for formation of proteins

Function of Ribosomes

• Ribosome reads the code on the mRNA in groups of three

• Each triplet of bases codes for a specific AA

• Carrier molecules bring specific AA to growing polypeptide chain in correct order (due to anti-codon being complementary)

• Ribosome translates the sequence of bases into a sequence of AA that make up a protein

• After AA chain has been assembled it is released from the ribosome so it can fold and form the final structure of a protein

Mutation

• Change in the base sequence of DNA

• (sometimes inherited)

When and where do mutations occur?

• Mutations occur continuously

• They can occur spontaneously eg. when a chromosome is replicated properly

• Chance of mutation is increased by exposure to certain substances

What factors increase risk of mutations occuring?

• Carcinogens → chemicals that cause cancer

• Certain types of radiation (x ray and gamma rays)

• These are risk factors that increase the CHANCE of mutations occurring

What is meant for a gene to be expressed?

• Cell is actively producing proteins that the gene codes for

• The gene is “switches on”

Non Coding DNA

• DNA that does not code for proteins

• Non-coding parts of DNA can switch genes on and off, so variations/mutations in these areas of DNA may affect how genes are expressed

Where are mutations most likely to occur?

• Non - coding DNA

Mutations and affect?

• change the sequence of DNA bases in a gene which produces a genetic variant

• mutations can sometimes lead to a change in protein that is coded for

• Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed

Serious affect with mutations

• few mutations code for an altered protein with a different shape

• change in base sequence → change in sequence of amino acid → fold up to form a different protein with different shape

• so can no longer carry out its function

  • Enzymes - enzyme may no longer fit the substrate binding site (active site changed)

  • structural protein like collagen may lose its strength

Insertion Mutation

- A new base is randomly inserted into the DNA sequence

-An insertion mutation changes the amino acid that would have been coded for by the codon

- An insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Substitution mutation

- A base in the DNA sequence is randomly swapped for a different base

- Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs (no knock on effect)

Deletion mutation

- A base is randomly deleted from the DNA sequence

- A deletion mutation changes the amino acid that would have been coded for by the codon

- A deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Mutation in Non Coding DNA

If a mutation occurs in a section of non-coding DNA the expression of these genes may be altered or in some cases the mutation may cause them not to be expressed at all

Effects of Mutations

- Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed

- Some mutations code for a significantly altered protein with a different shape

- This may affect the ability of the protein to perform its function.

Enzyme EXAM STYLE Q (if altered what is the effect)

• Change is base changes triplet/codon

• Changes amino acid it codes for (so different poly peptide sequence)

• This means the polypeptide will fold into a differently shaped protein/enzyme

• The protein/enzyme may have a differently shaped active site 

• So it may no longer be complementary to the substrate 

• Which would mean it couldn't form an enzyme-substrate complex

• So it couldn't catalyse the reaction as well / the rate would be lower

Sexual Reproduction

• New offspring are produced by the fusion of male and female gametes (fertilisation)

• Mixing of genetic information which leads to variety in the offspring

• Genetically unique offspring (different from parents)

• formation of gametes involves meiosis

Which two gametes fuse in animals?

• During sexual intercourse

• Sperm cell and Egg Cell

Which two gametes fuse in flowering plants?

• Pollen

• Egg Cell (Ovule)

Haploid

• Half number of normal chromosomes (23)

• eg. Sperm cell

Diploid

• Full number of chromosomes 46

• eg. Sperm + Egg cell fuse

Fertilisation

• Fusion of male and female gametes

• 23 Sperm Cell + 23 Egg Cell

• Fuse to form a zygote with full number of chromosomes

• Offspring inherits features from both parents as it receives a mixture of chromosomes from mother and father

Asexual Reproduction

• Type of reproduction where new offspring are produced by a single parent

• No fusion of gametes

• There is no mixing of genetic information → leads to genetically identical offspring (clones)

• Genetically Identical Offspring

• Only mitosis is involved

Different organisms (asexual/sexual reproduction?)

• Animals - Sexual Reproduction

• Fungi - Asexual Reproduction

• Plants - Both

• Bacteria - Asexual Reproduction (binary fission)

Meiosis vs Mitosis

• Meiosis → non identical cells being formed

• Mitosis → Identical cells being formed

3 Advantages of Sexual Reproduction

• It produces variation in the offspring, so the species is less likely to be wiped out by extreme events.

• If the environment changes, the variation will allow the species to adapt/evolve by natural selection.

• Humans can speed up natural selection via selective breeding to gain certain benefits (e.g. selectively breeding certain crops to increase food production).

3 Disadvantages of Sexual Reproduction

• It requires two parents.

• It can require large amounts of time and energy to search for a mate.

• Many species spend resources impressing their mates even though it doesn't aid survival.

3 Advantages of Asexual Reproduction

• Only one parent is needed.

• Takes less time as parents do not need to find a mate.

• It is faster than sexual reproduction.

• Genetically identical offspring → successful traits propagated

• Many offspring produced

2 Disadvantages to Asexual Reproduction

• Low genetic variation means that offspring are more susceptible to extreme events (like the spread of a new disease).

• The population would have a smaller chance of adapting to new conditions.

3 Examples of Organisms to reproduces Asexually and Sexually

• Malarial parasites reproduce asexually in the human host but sexually in the mosquito.

• Many fungi reproduce asexually by spores but also reproduce sexually to give variation.

• Many plants produce seeds sexually but also reproduce asexually – for example, by runners in strawberry plants or bulb division in daffodils.

Gamete

• Sex Cell such as sperm or egg cell

• 23 Chromosomes

Where in the body does meiosis take place?

• only in reproductive organs

• testes in males

• ovaries in females

• produces 4 genetically unique cells

• 2 divisions occur

How does meiosis halve the number of chromosomes in gametes and how does fertilisation restore the full number?

• Meiosis produces gametes (sperm and egg cells).

• It halves the chromosome number from 46 to 23.

• Each gamete contains 23 chromosomes.

• During fertilisation, sperm and egg fuse together.

• Their chromosomes combine (23 + 23).

• The zygote restores the full number of 46 chromosomes.

What happens when a cell forms a gamete?

• copies of the genetic information are made

• the cell divides twice to form four gametes, each with a single set of chromosomes

• all gametes are genetically different from each other

What happens after fertilisation during early development?

• Gametes join at fertilisation, restoring the normal chromosome number.

• The new cell (zygote) divides by mitosis.

• The number of cells increases.

• As the embryo develops, cells differentiate into specialised cells to make whole organism

Mitsios vs Meiosis

• Mitosis produces gentically identical cells while meiosis produce geneticall unqiue/varied cells

• Mitosis produces 2 daughter cells BUT meiosis produces 4 daughter cells

• Mitosis has one cell divison while mitsosi has two cell divisons

• mitosis produces diploid cells but meiosis produces haploid cells